Systems, devices and methods for transforming neutron beams - Patents.com

Abstract

Systems, devices, and methods are described for converting a raw neutron beam into a specific deliverable format with a targeted energy range, size, and direction. Neutron beam converter embodiments can include multiple regions based on location, function, size, and / or construction material. The regions can include a central region, a middle region, a peripheral region, and a front region. Materials are also described. In one embodiment, a neutron beam converter is configured to receive a raw neutron beam from a neutron generating target and output a converted neutron beam, the converted neutron beam having a relatively more focused forward direction than the raw neutron beam, a relatively smaller variation in intensity than the raw neutron beam, and a relatively smaller variation in energy than the raw neutron beam.

Description

[Technical field]

[0001] The subject matter described herein relates generally to systems, devices, and methods for converting a neutron beam from a raw form to a deliverable form. [Background technology]

[0002] Boron Neutron Capture Therapy (BNCT) is a modality for the treatment of various types of cancer, including some of the most challenging types. BNCT is a technique that aims to selectively treat tumor cells while sparing normal cells using boron compounds. The boron compounds allow efficient capture by various cell types and selective drug accumulation at the target site (e.g., tumor cells). The boron-loaded cells can be irradiated with neutrons (e.g., in the form of a neutron beam). The neutrons react with the boron and eradicate the tumor cells.

[0003] Neutron beams for BNCT can be generated by a variety of techniques. One such technique involves irradiating a suitable neutron generating target with a charged particle beam, such as a proton beam or a deuteron beam. The charged particles react with atomic nuclei in the target to release a beam of raw neutrons that can be used for BNCT. The neutrons are raw in the sense that immediately after their generation in the target, a significant portion of the neutrons may have propagated in various directions rather than directly toward the patient and may have energy levels that are too high or too low to be administered to the patient. Raw neutrons may also be accompanied by undesirable gamma radiation. Existing techniques for modifying raw neutrons suffer from shortcomings, including insufficient ability to redirect neutrons in a desired direction, insufficient ability to scatter neutrons into a desired energy range, and insufficient ability to remove undesirable photon and low energy neutron radiation. Thus, there is a need for improved systems, devices, and methods for neutron beam modification or transformation. Summary of the Invention [Means for solving the problem]

[0004] The subject matter described herein generally relates to systems, devices, and methods for converting raw neutron beams into specific deliverable formats with targeted energy ranges, sizes, and directions, as well as for removing undesired non-neutron radiation. An embodiment of a neutron beam converter (NBC) is described in the exemplary context of a BNCT system configured to output a neutron beam in an epithermal energy range. The NBC can include multiple regions based on location, function, dimensions, and / or construction materials. The regions can include a central region oriented along a beam axis between a beam input and a beam output of the NBC. The central region can be configured to primarily function to scatter high energy neutrons down to the epithermal range and achieve and / or maintain a forward beam (e.g., a beam propagating primarily toward the patient). The central region can perform other functions such as redirection and neutron absorption. The intermediate region can be located laterally outside the central region and can function to redirect neutrons back into the central region while scattering toward or into the epithermal range for output to the patient. The intermediate region can also absorb photons in the form of gamma radiation and scatter neutrons propagating away from the beam axis to epithermal and lower energy levels for easier absorption. The peripheral region can be located laterally outboard of the intermediate region and can function to absorb neutrons and scatter neutrons down to and into the epithermal and thermal energy ranges for absorbing photons in the form of gamma radiation. The front region can be located on the side of the NBC facing the patient and can function to scatter neutrons down to and into the epithermal and thermal energy ranges, absorb neutrons, and absorb photons in the form of gamma radiation. Numerous exemplary embodiments of NBC arrangements are disclosed that perform some or all of these functions in the central, intermediate, peripheral, and front regions. Numerous exemplary materials are disclosed that have the ability to perform one or more of these functions.

[0005] Other systems, devices, methods, features, and advantages of the subject matter described herein will become apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, be within the scope of the subject matter described herein, and be protected by the accompanying claims. Features of the example embodiments should in no way be construed as limiting the scope of the appended claims unless there is an express recitation of those features in the claims. [Brief description of the drawings]

[0006] Details of the subject matter described herein, both as to its structure and operation, may become apparent by examining the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the subject matter. Moreover, all figures are intended to convey concepts, and relative sizes, shapes, and other detailed attributes may be shown diagrammatically, rather than literally or precisely.

[0007] [Figure 1A] FIG. 1 is a schematic diagram illustrating an example of a neutron beam system according to the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram illustrating an example of a neutron beam system for use in boron neutron capture therapy (BNCT). [Figure 2A] FIG. 2 is a perspective view showing an example of a neutron generating target. [Figure 2B] FIG. 2 is a side view of an example of an assembly for containing a neutron generating target. [Figure 2C] FIG. 2 is a cross-sectional view of an example assembly for containing a neutron generating target. [Figure 3A] 1 is a cross-sectional view illustrating an exemplary embodiment of a neutron beam converter. [Figure 3B] FIG. 2 is a rear perspective view of an exemplary embodiment of a neutron beam converter. [Figure 4A]2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4B] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4C] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4D] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4E] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4F] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4G] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4H] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4I] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4J] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 4K] 2 is a cross-sectional view of an exemplary embodiment of a central region of a neutron beam converter; [Figure 5A] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5B] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5C] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5D] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5E] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5F]1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5G] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 5H] 1A-1C are cross-sectional views illustrating an exemplary embodiment of a stack-up configuration for a central region of a neutron beam converter. [Figure 6A] 1 illustrates a cross-sectional view of an exemplary embodiment of an intermediate region of a neutron beam converter. [Figure 6B] 1 illustrates a cross-sectional view of an exemplary embodiment of an intermediate region of a neutron beam converter. [Figure 7A] 2 is a cross-sectional view illustrating an example embodiment of a peripheral region of a neutron beam converter. [Figure 7B] 2 is a cross-sectional view illustrating an example embodiment of a peripheral region of a neutron beam converter. [Figure 8A] 2 is a cross-sectional view of an exemplary embodiment of a front region of a neutron beam converter; [Figure 8B] 2 is a cross-sectional view of an exemplary embodiment of a front region of a neutron beam converter; [Figure 9A] FIG. 2 is a cross-sectional view illustrating an exemplary embodiment of a neutron beam converter in a first configuration. [Figure 9B] FIG. 2 is a cross-sectional view illustrating an exemplary embodiment of a neutron beam converter in a first configuration. [Figure 9C] FIG. 2 is a cross-sectional view illustrating an exemplary embodiment of a neutron beam converter in a first configuration. [Figure 10A] FIG. 2 is a cross-sectional view illustrating an exemplary embodiment of a second configuration of a neutron beam converter. [Figure 10B] FIG. 2 is a cross-sectional view illustrating an exemplary embodiment of a second configuration of a neutron beam converter. [Figure 10C] FIG. 2 is a cross-sectional view illustrating an exemplary embodiment of a second configuration of a neutron beam converter. [Figure 11A] FIG. 13 is a cross-sectional view illustrating an exemplary embodiment of a third configuration of the neutron beam converter. [Figure 11B]FIG. 13 is a cross-sectional view illustrating an exemplary embodiment of a third configuration of the neutron beam converter. [Figure 11C] FIG. 13 is a cross-sectional view illustrating an exemplary embodiment of a third configuration of the neutron beam converter. [Figure 12] 1A-1C are perspective views illustrating a portion of an example embodiment of a neutron beam converter having various transition surface geometries. [Figure 13] 1A-1C are perspective views illustrating a portion of an example embodiment of a neutron beam converter having various transition surface geometries. [Figure 14A] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14B] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14C] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14D] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14E] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14F] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14G] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14H] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14I]1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14J] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14K] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14L] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14M] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14N] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14O] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14P] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; [Figure 14Q] 1 is a graph of cross section versus neutron energy for various types of materials suitable for use within an exemplary embodiment of the neutron beam converter; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present disclosure is not limited to the particular embodiments described, which may, of course, vary. The scope of the present disclosure will be limited only by the appended claims, and the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0009] The term "particle" is used broadly herein, and unless otherwise limited, can be used to describe an electron, a proton (or H+ ion), or a neutron, as well as species having two or more electrons, protons, and / or neutrons (e.g., other ions, atoms, and molecules).

[0010] Described herein are exemplary embodiments of systems, devices, and methods for neutron beam transformation that can be used in conjunction with neutron beam systems (including, for example, nuclear reactors or particle accelerators). The embodiments described herein can be used with any type of neutron beam system in which neutron beam transformation or modification is desired. The embodiments herein can be used in numerous applications, one example being a neutron beam system for generating neutron beams for use in boron neutron capture therapy (BNCT). BNCT uses a beam of epithermal neutrons (e.g., with an energy spectrum of 1 electron volt (eV) to 30 kiloelectron volts (keV)) for cancer treatment. In BNCT, neutrons can be generated from nuclear reactions of charged particles (e.g., proton beams) colliding with either beryllium or lithium target devices. The generated neutron beams have a wide range of energies and are emitted in a variety of directions. The target can therefore be contained within a larger Neutron Beam Converter (NBC), which functions to convert the generated neutron beam into a primary forward beam within the desired epithermal energy range, which is then output to the patient.

[0011] The exemplary embodiments of neutron beam converters described herein are not intended to be viewed in isolation from one another. All features, elements, components, and functions described with respect to any converter embodiment provided herein are intended to be freely combinable and substitutable with features, elements, components, and functions from any other converter embodiment. When a particular feature, element, component, and function is described with respect to only one converter embodiment, that feature, element, component, and function can be used with all other converter embodiments described herein, unless expressly specified otherwise. Thus, this paragraph serves as a predicate and written support for the introduction of claims that, whenever, combine features, elements, components, and functions from different converter embodiments or substitute features, elements, components, and functions from one converter embodiment with features, elements, components, and functions from another converter embodiment, even if the following description does not expressly state that such combinations or substitutions are possible in a particular case. It is expressly acknowledged that an explicit enumeration of all possible combinations and substitutions would be unduly burdensome, especially considering that the permissibility of each and every such combination and substitution would be readily recognized by a person skilled in the art.

[0012] Neutron beam system example For ease of explanation, the embodiments described herein are done so in the context of generating neutron beams for use in BNCT, however the embodiments are not so limited, and may be applied to other applications that generate significant neutron radiation, even outside of BNCT applications that utilize different energy ranges.

[0013] FIG. 1A shows a schematic diagram of an exemplary embodiment of a system 100 for use in BNCT according to the present disclosure. The system 100 is configured to generate and propagate a charged particle beam to a target 60 to generate a neutron beam 70, which is directed to a patient's body 80 to be irradiated. The beam system 100 includes a charged particle source 20, a low energy beam line (LEBL) 30, an accelerator 40, and a high energy beam line (HEBL) 50. The source 20 is configured to generate a charged particle beam that is output to the LEBL 30. The LEBL 30 is configured to transport the beam from the source 20 to the accelerator 40. The accelerator 40 is configured to accelerate the charged particle beam to a higher energy. The HEBL 50 extends from the accelerator 40 to a target 60 housed within a target assembly portion of the HEBL 50. The HEBL 50 delivers the charged particle beam from the output of the accelerator 40 to a target 60 , where the charged particle beam is converted into a neutron beam 70 .

[0014] The neutron beam converter (NBC) 200 is positioned proximate to and around the target 60 and performs various functions on the neutrons of the beam 70 emanating from the target 60. These functions include reducing the energy of the generated neutrons from energies above a desired range to within a desired range, focusing the generated neutrons in a forward direction toward the patient, removing generated neutrons that are outside of the desired range, and removing other radiation by-products (e.g., photons, etc.) at undesirable energy levels. The desired neutron energy range may vary based on the application. For BNCT applications described herein, the desired energy range may be, for example, 1 eV to 10 keV or 1 eV to 30 keV, with the neutron distribution peaking near the upper end of the desired range. For example, a 1 eV to 30 keV beam may be configured to output at least 90% of the neutrons within that energy range with a peak neutron distribution and a mean energy of 10 keV to 30 keV. As another example, a 1 eV-10 keV beam may be configured to output at least 90% of neutrons in an energy range having a peak neutron distribution and an average energy of 3 keV-10 keV. For convenience, these ranges are described as epithermal energy ranges. Neutrons with energies below these ranges are referred to as thermal neutrons (e.g., below 1 eV) and neutrons with energies above these ranges are referred to as fast neutrons (e.g., above 30 keV).

[0015] 1B is a schematic diagram illustrating an exemplary embodiment of a beam system 100 configured as a neutron beam system for use in BNCT. The beam system 100 includes a preaccelerator system 26 forming at least a portion of the LEBL 30, which functions as a charged particle beam injector. The system 100 includes a high voltage (HV) tandem accelerator 40 coupled to the LEBL 30, and a HEBL 50 extending from the tandem accelerator 40 to a target 60, as described with reference to FIG. 1A.

[0016] The LEBL 30 transports the negative ion beam (e.g., H-ions) from the ion source 20 to the input (e.g., input aperture) of the accelerator 40 via a preaccelerator 26, which raises the energy level of the ion beam and focuses it. The accelerator 40 is powered by a high voltage power supply 42 coupled to it. The accelerator 40 includes a vacuum tank, a charge exchange tube, acceleration electrodes, and a high voltage feedthrough. The accelerator 40, in some implementations, can accelerate a hydrogen ion beam to produce a proton beam having an energy approximately equal to twice the voltage applied to the acceleration electrodes positioned within the accelerator 40. The energy level of the proton beam can be achieved by accelerating a beam of negative hydrogen ions from the input of the accelerator 40 to the innermost high potential electrode, stripping two electrons from each ion, and then accelerating the resulting protons downstream through the same voltages encountered in reverse order.

[0017] The HEBL 50 can transport the proton beam from the output of the accelerator 40 to a neutron generating target 60 positioned at the end of a beamline branch 71 that extends into a patient treatment room. The beam system 100 can be configured to direct the proton beam to one or more targets 60 and associated target areas. In some implementations, the HEBL 50 includes multiple (e.g., three) branches 71, 81, and 91 configured to extend to multiple different patient treatment rooms, with each branch terminating at a target 60 and an NBC 200. The HEBL 50 includes a pumping chamber 51, quadrupole magnets 52 and 72 to prevent beam defocusing, dipole or bending magnets 56 and 58 to steer the beam toward one or more targets, a beam corrector 53, diagnostics such as current monitors 54 and 76, a fast beam position monitor 55 section, and a scanning magnet 74 for branch 71. Branches 81 and 91 can include similar components as branch 71.

[0018] The design of the HEBL 50 depends on the configuration of the treatment facility (e.g., one floor treatment facility, two floor treatment facility, etc.). The beam can be delivered to the target 60 (e.g., positioned near a treatment room having a patient 80) using a deflection magnet 56. A quadrupole magnet 72 can be included to focus the beam to a particular size at the target 60. The beam can pass through one or more scanning magnets 74, which provide lateral movement of the beam onto the target surface in a desired pattern (e.g., spiral, curved, stepped in rows and columns, combinations thereof, etc.). The lateral movement of the beam allows for the creation of a smooth, uniform time-averaged distribution of the proton beam on the target 60, prevents overheating of the target, and allows for particle (e.g., neutron) production to be as uniform as possible within the target (e.g., neutron production layer 121 of FIG. 2A).

[0019] The scanning magnet 74 may be configured to direct the beam to a current monitor 76 that measures the beam current. The beam current value may be used to activate a safety interlock. The target assembly 65, including the target 60, may be physically isolated from the high energy beamline volume using a valve 77. The function of the valve 77 is to isolate the vacuum volume of the beamline from the target 60 during removal of the used target and loading of a new target. In some implementations, the beam may be directed straight to one or more quadrupole magnets 52 located in the horizontal beamline instead of being deflected 90 degrees by the deflection magnet 56. The beam may be bent to a pre-set angle by another deflection magnet 58 depending on the setup requirements (e.g., patient location or room configuration). In some implementations, the deflection magnet 58 may be split and placed in the beamline and configured to direct the beam in one of two directions to two different treatment rooms located on the same floor of a medical facility.

[0020] 1B is one example of different configurations that can be used to generate charged particle beams and neutron beams. Different configurations of system 100 can utilize accelerators other than electrostatic tandem accelerators and can utilize targets that are either stationary or rotating. The NBC 200 embodiments described herein are not limited to use with any one type of neutron beam generation system.

[0021] 2A is a perspective view of an exemplary embodiment of a target 60. In this embodiment, the target 60 has a neutron-generating layer 121 with a charged particle receiving surface 122. The neutron-generating layer 121 is positioned on or near a substrate 123. In some cases, the layer 121 is covered with one or more other layers for protection. The layer 121 may also have one or more underlayers between the layer 121 and the substrate 123, for example, to resist blistering. A charged particle beam, such as a proton beam, incident on the surface 122 enters the target 60 and causes a reaction in the layer 121 that generates neutrons. This is the Li-7(p,n)Be-7 nuclear reaction when the neutron-generating layer 121 is made of lithium-7. Alternatively, the neutron generating layer 121 may be beryllium-9 and the neutrons may be generated with a proton beam (Be9(p,n)B9) or a deuteron beam (Be9(d,n)B10) of different energies. The substrate 123 may be a material with good thermal conductivity, such as copper or aluminum, to aid in the removal of heat generated by the reaction.

[0022] FIG. 2B is a side view of an exemplary embodiment of a target assembly 65 that may form a terminal portion of the HEBL 50. The target 60 (not shown) may be housed within the assembly 65 at or near end 67. The charged particle beam enters the assembly 65 at end 66 and travels to the opposite end 67 where it impinges on the target 60. Various cooling channels 68 are routed to and from end 67 for the insertion and removal of coolant used to regulate the temperature of the target 60 during use. A number of sensors may be included to monitor the temperature and radioactivity of the assembly 65 and its surroundings. Also shown is a valve 77 in the form of a gate valve. The end 67 of the assembly 65 is inserted into an opening 205 ( FIG. 3A ) in the NBC 200 and remains there during the BNCT procedure. When the assembly 65 (with the target 60) reaches the end of its usable life, it may be removed from the NBC 200 and discarded, at which point a new assembly 65 and target 60 may be inserted into the NBC 200.

[0023] FIG. 2C is a cross-sectional view of an exemplary embodiment of the target assembly 65, omitting for clarity components such as valves 77, coolant channels, and sensor connections. The sidewall 62 has a tubular shape and includes an interior space 64 with a vacuum or near vacuum level. The target 60 is positioned at the end 67 and held in place by an end cap 63. Variations of this structure are possible, such as a target 60 surrounded by the sidewall 62. The charged particle beam 61 is guided through the interior space 64 and scanned across the target 60 by a scanning magnet 74 located upstream of the HEBL 50 (not shown). Neutrons generated by the target 60 are emitted at some level from the target 60 in substantially all directions, although the majority of the neutrons are emitted in a divergent but generally forward-directed path. This is shown here in raw form as a neutron beam 70.

[0024] Exemplary embodiments of a neutron beam converter 3A is a cross-sectional view of an exemplary embodiment of a neutron beam converter (NBC) 200. The NBC 200 includes a target assembly aperture 205 configured to receive a target assembly 65 (not shown). In an assembly configuration such as that described with respect to the embodiment of FIG. 2B, installation of the assembly 65 within the aperture 205 positions the target 60 at a target installation location 69. Some amount of clearance exists between the assembly 65 and the surrounding walls of the NBC 200, for example to allow for routing of coolant channels and periodic replacement of the assembly 65, although generally an interference fit may be desired.

[0025] The NBC 200 is configured to have a beam input 201 adjacent or proximate to a target placement location 69. In some embodiments, the distance between the input 201 and location 69 is between 10 and 60 centimeters (cm), more preferably between 25 and 40 cm. The NBC 200 has a beam output 202 downstream of the generated neutron flow, which is located proximate to a recess 206. An axis 203 extends from the input 201 to the output 202, which in this embodiment is approximately centrally located within the NBC 200. For convenience, the location of elements within the NBC 200 will be referenced with respect to the axis 203 and a lateral direction 204 perpendicular to the axis 203. The terms upstream and downstream are referenced with respect to the charged particle beam flow to the target and the subsequent neutron flow, both of which generally proceed in a direction from left to right in FIG. 3A (e.g., from the input 201 to the output 202 along the axis 203). For example, the opening 205 is axially upstream of the recess 206 .

[0026] The NBC 200 has a rear (upstream-most) surface or side 301, a front (downstream-most) surface or side 302, and a lateral surface or side 303. The NBC 200 includes four general regions: a central region 210, an intermediate region 230, a peripheral region 250, and a front region 270, which are intersected by an axis 203. In this embodiment, the central region 210 has a generally cylindrical shape. The intermediate region 230 also has a generally cylindrical shape and surrounds the lateral and upstream sides of the central region 210. The peripheral region 250 also has a generally cylindrical shape and surrounds the lateral and upstream sides of the intermediate region 230. The regions 210, 230, and 250 can be configured to form a generally concentric housing about the axis 203, the housing being a concentric cylindrical or pseudo-cylindrical multi-sided shape.

[0027] Various cylindrical shapes allow tailoring of neutrons emitted from the target 60 on all lateral sides of the beam axis. The shapes can be symmetric in both axial and lateral profiles, or asymmetric in one or both profiles. An asymmetric axial profile can have a variable diameter that increases or decreases going from upstream to downstream (see section 251 of Figures 11A-11C). An asymmetric lateral profile can have a variable diameter when viewed in lateral cross section (e.g., elliptical cross section).

[0028] Front region 270 spans downstream of regions 210, 230, and 250, but does not necessarily contact each region. Recess 206 may be filled with a vacuum or ambient gas to aid in forming neutron beam 70 in a forward direction. NBC 200 may be mounted in a structural support 95 that maintains NBC 200 in position relative to upstream neutron beam system 100 and downstream patient treatment room. FIG. 3B shows a perspective view of an exemplary embodiment of NBC 200 from the upstream side. In this embodiment, structural support 95 is a concrete BNCT facility wall.

[0029] Each of the regions 210, 230, 250, and 270 is configured to perform a different set of functions on the neutrons and other particles generated by the system 100. The central region 210 has the primary function of scattering fast neutrons emitted from the target 60 in a forward direction without significantly changing direction and without absorbing significant amounts of the neutrons. The fast neutrons are preferably scattered such that their energy falls within and remains within the target range (e.g., epithermal energy) until they are output from the NBC 200. This is preferably done without simultaneously scattering a significant number of neutrons outside the target range.

[0030] The amount and type of material in the central region 210 is proportional to the change in energy required in any given direction to scatter and reduce the most likely neutron energy emitted in that direction. For example, neutrons emitted from the target 60 in the forward direction are more energetic than neutrons traveling in the backward direction, so more material is required in the forward direction.

[0031] Intermediate region 230 functions to redirect neutrons into central region 210, conserving those neutrons but allowing them to be utilized in beam 70 in a manner that results in minimal energy loss and absorption. Region 230 also scatters fast neutrons emitted at large forward angles from target 60 that traverse laterally through central region 210, and provides photon shielding for prompt gamma rays generated by neutron capture in both central region 210 and peripheral region 250.

[0032] Periphery region 250 functions to remove neutrons of all energies, as it is unlikely that those neutrons can be redirected back into central region 210. This is accomplished by scattering the neutrons further to thermal or near-thermal energy levels for easier absorption by region 250. Region 250 also provides photon shielding to reduce the number of photons generated in the interior areas of NBC 200 from entering the facility.

[0033] The effectiveness of a material to scatter and reduce the energy of neutrons is inversely proportional to its atomic mass number, A, which is governed by the number of protons and neutrons in the nucleus. The maximum and average fractional energy loss of a material is approximated by the following equation:

number

[0034] As an example, the hydrogen nucleus (A

number

number

number

number

number

[0035] The number of collisions a neutron must undergo, on average, to down-scatter to a particular energy from an incident neutron energy, is based on another parameter, ζ, which is given by the relationship:

number

[0036] The number of collisions, N, can be approximated using the following relationship:

number

[0037] From this formula, it can be seen that, on average, 24 times more collisions are needed for lead than for beryllium to reduce the incident neutron energy by half.

[0038] Each material is calculated based on its mass plus its total macroscopic cross section (

number

[0039] The type and amount of material present in each region can be selected to perform these various functions. Materials that are good at scattering neutrons, generally classified herein as "S" materials, can be further classified as having a substantial cross section for scattering from fast to epithermal energies ("Fast-S"), scattering from fast and epithermal energies to lower energies ("Epi-S"), and having a substantial cross section in the non-resonant region for scattering fast and / or epithermal neutrons ("NR-S"). Different scattering materials, regardless of class, can be designated by a numerical suffix (e.g., S1, S2, and S3). Materials that are good at absorbing thermal neutrons are generally referred to herein as "Ab" materials. Materials that are good at redirecting neutrons are generally referred to herein as "R" materials.

[0040] Exemplary Fast-S Materials Particularly useful Fast-S elements can have an atomic number (Z) of 9 or greater, examples of which are magnesium, fluorine, and aluminum. 2 ), magnesium, and aluminum. As can be seen, fluorine (about 27 keV) and aluminum (about 33 keV) lie between the epithermal and fast neutron energy regions at 30 keV (3×10 -2The Fast-S material has a significant resonant peak 1400 that begins close to the 1 MeV (100 keV) transition, which continues at intervals therefrom as the energy increases. Fast neutron scattering occurs either in a relatively low energy region with discrete resonant peaks, or in a relatively high energy, unresolved resonant region where the resonant peaks are so closely spaced and close together in energy that they effectively no longer look like individual resonances. The Fast-S material selected for the NBC 200 preferably has a resonant region that begins at the upper end of the target energy (e.g., epithermal) region required for a particular treatment. Magnesium has an initial resonant peak at 20 keV, then again at about 80 keV and higher energies. Neutrons with fast energies that coincide with these resonant peaks are relatively more likely to be scattered, and thus decrease in energy, toward the epithermal region. Conversely, neutrons in the epithermal region are less likely to be scattered by these materials as they travel through them, allowing the neutrons to remain within the desired energy region until they exit the NBC 200 and reach the treatment site in the patient.

[0041] Aluminum is a very versatile material with structural strength, relatively easy manufacturing, and the ability to be combined with other elements in a wide variety of compounds. Aluminum alloy blends are divided into three different categories based on the alloying material, which can be other elements such as magnesium and silicon, which have desirable scattering properties. Aluminum 6000 series alloys contain over 97% aluminum (by weight percent), with the remaining elements being either silicon or magnesium. Aluminum 5000 series alloys contain over 90% aluminum, with the major alloying element being up to 10% magnesium. Some 5000 series cast metals may have only 32% aluminum, with the remainder being magnesium. Aluminum 4000 series alloys contain over 85% aluminum and up to 12.5% ​​silicon, with the remainder being magnesium, manganese, or copper. Some 4000 series cast metals may have up to 22% silicon.

[0042] The scattering properties of fluorine can be effectively utilized within the NBC 200 with one or more other materials in the form of a compound. For example, fluorine can be used as an alloy with aluminum (e.g., AlF 3 ), titanium (e.g., TiF 3 ), barium (e.g., BaF 2 ), bismuth (e.g., BiF 3 ), lead (e.g., PbF 2 ), tungsten (e.g., WF 6 ), vanadium (e.g., VF 3 ), magnesium (e.g., MgF 2 ), calcium (e.g., CaF 2 ) or carbon and hydrogen (e.g., ethylene tetrafluoroethylene (ETFE, C 4 H 4 F 4 The fluorine content is generally about 15% by weight (lead fluoride (PbF 2 ) to 54 mass% (TiF 3 ) or 68 mass% (AlF 3 FIG. 14B shows the relationship between magnesium fluoride (MgF 2 ), lead fluoride (PbF 2 ), and bismuth fluoride (BiF 3 ) As used herein, the term fluorine is intended to encompass the element itself and fluorides.

[0043] Materials within the NBC 200 that experience relatively high radiation exposure, such as in the central region 210, preferably exhibit sufficient radiation resistance to prevent degradation within the NBC 200. In various embodiments, the materials of the NBC 200 are radiation resistant to a minimum of 10,000 Grays (Gy). 2 F 4 Some fluorine-containing polymers, such as NBC200, have poor radiation resistance such that physical changes (e.g., decomposition, disintegration) can occur at as little as 100 Gy and are therefore not suitable for NBC200.

[0044] The fast scattering effects of aluminum and fluorine can be enhanced by combining these elements with magnesium into compounds of two or more elements, such as magnesium fluoride (see FIG. 14A) and the aluminum 4000, 5000, and 6000 series. Magnesium can be combined with a number of other S materials desirable for scattering, such as zinc, manganese, and silicon, for use within the NBC 200. All of the aforementioned Fast-S exemplary materials can be used in embodiments of the NBC 200 alone, in combination with each other, or in combination with other materials (e.g., Epi-S, NR-S, Ab, R) to achieve the desired structural properties and scattering capabilities.

[0045] Exemplary Epi-S Materials The Epi-S elements of the NBC 200 may have atomic numbers (Z) of 12 or greater. Particularly useful examples of these Epi-S elements are titanium and vanadium, and to a lesser extent magnesium. FIG. 14C is a graph showing the cross sections of titanium, vanadium, and magnesium within the epithermal energy region, from which the large resonant cross sections 1402 of titanium and vanadium within the upper epithermal range are visible. Titanium and vanadium can be used in combination with each other, in combination with other elements, or alone within the NBC 200. Titanium and vanadium can be easily combined with aluminum (or another Fast-S material) to take advantage of its Fast-S scattering potential. A typical titanium alloy has both vanadium and aluminum, with the aluminum content ranging from 6 to 30% (weight percent), while the vanadium content can range from 2.5 to 4.0%. Titanium and aluminum alloys (without vanadium) can be used, with as little as 12% or as much as 35% aluminum. Alloys of titanium and vanadium (without aluminum) can be used and can have as little as 10% vanadium up to 81% vanadium, the remainder being titanium. As with aluminum, some titanium compounds can contain as much as 10% silicon, while vanadium can be a silicide (VS2 , V.S. 3 Other examples of Epi-S materials include scandium (Sc), nickel (Ni), and zinc (Zn). All of the aforementioned Epi-S example materials can be used in embodiments of the NBC 200 alone, in combination with each other, or in combination with other materials (e.g., Fast-S, NR-S, Ab, R) to achieve desired structural properties and scattering capabilities.

[0046] Exemplary NR-S Materials Certain elements exhibit a broad non-resonant region for the cross section at lower energies after the end of the 1 / V region, extending to higher energies where the resonant cross section begins. The non-resonant region of the cross section can have a constant slope, e.g., a flat slope, and can be decreasing (to an extent substantially less than the 1 / V region) or constant. These elements are referred to herein as non-resonant scattering materials ("NR-S"), examples of which include hydrogen, lithium, boron, beryllium, carbon, nitrogen, and oxygen. In many embodiments, the NR-S materials exhibit a deviation of 20% or less over the target energy range (e.g., epithermal), more preferably 10% or less (e.g., as in the cross section of carbon up to about 120 keV).

[0047] FIG. 14D shows the structure of carbon, beryllium, and water (H 2 14 is a graph showing a cross section of the NR-S element 1402 (O). Carbon and beryllium have a non-resonant scattering region 1404 with a zero or near-zero slope from about 0.05 eV to 50 keV. Water has a non-resonant scattering region with a relatively small negative slope from about 0.05 eV to 10 keV. All NR-S elements can be used in embodiments of NBC 200 alone, in combination with each other, or in combination with other materials (e.g., Fast-S, Epi-S, R) to achieve desired structural properties and scattering capabilities.

[0048] Exemplary Ab Materials Certain elements exhibit broad 1 / V regions with significant cross sections that can extend over at least a substantial portion of the thermal and epithermal energy regions. The 1 / V region of the cross section can have a constant slope, e.g., a flat slope, or can decrease with a substantial slope. These elements are particularly useful for absorbing neutrons and are referred to herein as absorbing materials ("Ab"), examples of which include hydrogen, lithium, boron, and carbon. These materials can be referred to as either Ab materials or NR-S materials, depending on the context. FIG. 14E is a graph showing the cross sections of carbon, boron, and lithium. Boron has a 1 / V region 1410 that extends over most of the thermal energy and epithermal energy regions up to about 10 keV, and lithium's 1 / V region 1410 extends over both the thermal and epithermal regions up to about 50 keV.

[0049] FIG. 14O shows lithium titanate along with two Epi-S materials, titanium-aluminum-vanadium alloy (Ti-6Al-4V) and titanium dioxide (TiO2). FIG. 14P shows titanium diboride along with Ti6Al4V and Fast-S aluminum-magnesium compounds in the Epi-S material. FIG. 14Q shows boron carbide (B) along with titanium aluminate and Fast-S aluminum-magnesium compounds in the Epi-S and NR-S materials. 4 C). As can be seen, lithium titanate, titanium diboride, and boron carbide have significant 1 / V regions that extend across most of the epithermal energy range. Both lithium titanate and titanium diboride have significant resonant peaks in the higher epithermal energy range, and boron carbide has a significant cross section across the entire epithermal energy range, which contributes to the usefulness of these materials in scattering epithermal neutrons for absorption. Thus, materials with lithium or boron make excellent neutron absorbers and can also be used as important Epi-S materials.

[0050] Ab materials may be used in areas of the NBC 200 where neutron rejection is desired (e.g., near the rear and side edges of the NBC 200, and near the front on the surfaces surrounding the output section 202). All Ab elements may be used alone, in combination with each other, or in combination with other materials (e.g., Fast-S, Epi-S, NR-S, R) in embodiments of the NBC 200 to achieve desired structural properties and absorption capabilities. Further examples of combinations include hydrogen-containing materials such as polymers like polyethylene (PE) and boronized polyethylene (B-PE). Further examples of Ab materials include cadmium (Cd), gadolinium (Gd), indium (In), and hafnium (Hf).

[0051] Exemplary R materials Certain elements tend to redirect neutrons by elastic scattering with minimal neutron energy loss. This process is proportional to the Z value of the element as opposed to the structure of the cross section. Elements with Z values ​​greater than or equal to 74 (tungsten) and less than or equal to 92 (uranium) are particularly good at redirecting neutrons and are generally referred to herein as redirecting ("R") materials. These materials are also good at absorbing gamma radiation. FIG. 14F is a graph showing cross sections for R materials tungsten, bismuth, and lead across thermal and epithermal energies, while FIG. 14G is a graph showing the same cross sections for energies from 1 keV to 1 MeV. Of the three materials, tungsten has the largest cross section outside of the resonant peak and therefore the greatest scattering capability. All R elements may be used in NBC200 embodiments alone, in combination with each other (e.g., lead and bismuth alloys (e.g., 40-50 wt.% Pb)), or in combination with other materials (e.g., Fast-S, Epi-S, NR-S, Ab) in areas where increased redirection and / or increased gamma radiation shielding is desired. For example, NBC200 may use one or more R materials in combination with one or more S materials (e.g., PbF as shown in FIG. 14B) to redirect neutrons with minimal energy loss into collisions with materials that have the desired scattering properties (Fast-S, Epi-S, NR-S) to locally increase the number of energy-reducing neutron collisions that occur. 2 and BiF 3 ) (generally referred to herein as "R+S" combinations).

[0052] Exemplary carbide, nitride, and oxide compounds for non-resonant effects Carbon, nitrogen and oxygen are NR-S materials that can be combined with other scattering elements to add or enhance the non-resonant scattering capabilities of the overall material. For example, aluminum can be combined with oxides (e.g., Al 2 O 3 ), carbides (e.g., Al 4 C 3), and Fast-S elements that can be formed as nitrides (e.g., AlN). Examples of each are shown in the cross section vs. energy graphs of FIG. 14H. When aluminum is formed into an oxide, carbide, or nitride compound, the resonance cross section of the resulting material is equal to that of bare aluminum, but the cross section in the gap is significantly higher, as evidenced by the cross section in gap 1420 in FIG. 14H. Thus, aluminum has a higher average cross section in the epithermal and fast energy regions due to the addition of NR-S material. Similar gap enhancement results can be obtained when other Fast-S, Epi-S, and NR-S elements (e.g., magnesium, titanium, vanadium, beryllium, lithium, boron, hydrogen, and / or fluorine) are formed into oxides, nitrides, carbides, or carbonates. Aluminum oxide and titanium oxide can be combined with other elements (X) to form aluminates (X+Al 2 O 3 ) or titanates (X+TiO 2 ) In such combinations, the oxygen, nitrogen and carbon content is preferably 20-80% by weight of the total material. Oxides, nitrides and carbides are advantageous in that they can be easily sintered into many complex shapes. Any of the embodiments of NBC200 can be implemented using one or more oxides, carbides and / or nitrides.

[0053] Exemplary embodiments of the central region The selection of materials and material dimensions depends on the energy profile of the neutrons produced by a particular target 60. Because the neutron energy profile depends on the design, materials, and construction of the target 60, as well as the characteristics (e.g., energy and current) of the incident charged particle beam or other mechanism utilized to generate neutrons, numerous example embodiments of the NBC 200 are disclosed herein.

[0054] Some of these embodiments utilize a stacked or layered arrangement in which sections having different materials are placed adjacent to each other to form a sequence that acts on the neutrons passing therethrough. Such stacked arrangements allow more complex functions to be performed on the neutrons in terms of scattering, redirecting, and absorbing different energies. The stacked layers allow a relatively high degree of tunability of the effects for a particular raw neutron profile. These effects can be tuned axially and laterally along all directions of neutron propagation from the target 60 by stacking the layers along the axis 203 (see Figures 4A-4E and 4G-4K) and laterally along the direction 204, for example, as in the cross-sectional arrangement of the central region 210 and the intermediate region 230 (see Figures 6A-6B).

[0055] 4A-4K are axial cross-sectional views of exemplary embodiments of central region 210 having different arrangements of one or more materials. In these embodiments, central region 210 is bisected with beam input 201 oriented at the bottom and beam output 202 oriented at the top. Each of the embodiments includes a shell 208 extending from input 201 to output 202. Shell 208 can be, for example, in the form of a tubular wall having a circular, elliptical, polygonal, or other cross-sectional profile. These embodiments can also be implemented without shell 208 (e.g., FIG. 4E). Surrounded by shell 208 are one or more sections or regions (e.g., 211, 212, and / or 213), each intersected by beam axis 203. Each section can include a different material, can have different dimensions from all other sections (i.e., such that no two sections are the same), or the same or similar sections can be repeated (in terms of dimensions and / or materials) and combined with one or more sections having different materials and / or dimensions. Central region 210 may include one, two, three, four, or more distinct sections, each of which may be repeated two or more times.

[0056] In these embodiments, the shell 208 can extend upstream beyond the location of the target 60. The shell 208 can terminate upstream within the NBC 200 or can extend all the way to the upstream end (e.g., the rearmost face) of the NBS 200. The upstream end of the shell 208 can be offset away from the assembly 65, as shown in FIG. 4A, or can include an inwardly extending flange or lip that closes on the assembly 65, as shown in FIG. 4B. The shell 208 can form a relatively low resistance path for neutron travel compared to paths adjacent to the shell 208. For example, the shell 208 can be an S material with a relatively low tendency to turn such that neutrons entering the shell 208 are transported to the beam output 202 with any necessary downward scattering to the epithermal range.

[0057] In the embodiment of Figures 4A-4C, the first section 211 is adjacent to the beam input section 201 and the second section 212 is between the section 211 and the beam output section 202, so that the sections 211 and 212 are stacked. The shell 208 can be complemented with one or more other materials at the output section 202 by an output liner 209, as shown in Figure 4C, which can be S and / or R materials to aid in forward beam formation. Figure 4D shows an exemplary embodiment with three stacked sections 211-213. Neutrons passing from the target 60 through the central region 210 pass through the sections 211, 212, and 213 in sequence. Figure 4E shows an exemplary embodiment similar to Figure 4D, but without the shell 208. The recess 206 is in the sidewall extending outwardly of the section 213.

[0058] 4F-4H show an exemplary embodiment in which at least one of sections 211, 212, and 213 is repeated in an interlaced manner with at least one of the other sections 211, 212, and 213. Neutrons passing from target 60 through central region 210 pass through sections 211, 212, and 213 in the order of their arrangement from upstream to downstream along axis 203. In FIG. 4F, sections 211-1, 211-2, and 211-3 are separated by one of sections 212-1 and 212-2. Sections 211-3 and 213-1 are separated by section 212-3. Sections 213-1 and 213-2 are separated by section 212-4. In FIG. 4G, section 211 includes a combination of R material and a first type of S material (S1), with no additional stacking or layering within section 211. In Figure 4G, section 212-1 is located axially downstream of section 211, followed by section 213-1, followed by section 212-2, followed by section 213-2. In Figure 4H, sections 211-1 through 211-3 and 212-1 through 212-3 are configured similarly to the embodiment of Figure 4F, with only one section 213 located downstream. Other stacking configurations can be utilized for central region 210, these are just a few examples.

[0059] In the embodiment of FIG. 4I, an internal non-solid space 207 is present in the beam input section 201, so that neutrons emitted by the target 60 traverse the non-solid space before reaching the continuous solid or semi-solid section 216, which may be a single section containing a mixture of one or more of the materials used in the discrete sections 211, 212, and 213 of the previous embodiment. In other words, one, two, or three of the materials of the discrete sections 211, 212, and 213 may be mixed to form the single section 216. In FIG. 4J, axially downstream of the section 216 is a section 214 containing an epithermal scattering material (Epi-S), followed by a section 215 containing an absorbing material (A). Such a configuration may be used to remove lower energy epithermal neutrons from the resulting beam 70, for example, by scattering the neutrons down in section 212 to an energy range more easily absorbed by section 213. FIG. 4K is an example of a shell 208 and a central region 210 having only one section 216.

[0060] Each section 211, 212, and 213 preferably includes or is formed of a different scattering (S) material, such that the S material of section 211 (denoted by S1) is different from the S material of section 212 (denoted by S2), which in turn is different from the S material of section 213 (denoted by S3 for embodiments having section 213). Shell 208, if present, can also include an S material that is the same (S1, S2, or S3) or different (S4) from the S material of sections 211, 212, and 213. The S material of sections 211, 212, 213 and shell 208 can be Fast-S, Epi-S, or NR-S type, or a combination of any two or three types. In embodiments where the desired energy output is in the epithermal range, the S material is preferably either a Fast-S or NR-S material.

[0061] The following table shows exemplary embodiments of material combinations that can be used within central region 210. Each of sections 211, 212, and 213 can be combined with redirecting (R) material, if desired. The combination with R material enhances the amount of local scattering since a passing neutron can be redirected multiple times by the R material without significant loss of energy, thus increasing the likelihood that it will preferentially encounter and scatter through the S material according to the S material resonant or non-resonant cross section.

[0062] Table 1 shows four examples of embodiments having two sections 211 and 212 and no shell 208. Tables 2A and 2B show 16 examples of embodiments having two sections 211 and 212 and a shell 208, which may be the same material (S1 or S2) as sections 211 and 212 or a different material (S3), with or without R material. With reference to Table 1, Example 1 ("Ex. 1") shows a configuration in which section 211 includes a combination of R and S1 materials and section 212 includes S2 material that does not include R material (indicated by the absence of "R"). Example 2 ("Ex. 2") shows a configuration in which section 211 includes S1 material that does not include R material and section 212 includes a combination of R and S2 materials. Example 3 ("Ex. 3") shows a configuration in which section 211 includes S1 material and section 212 includes S2 material, neither of which has R material. Example 4 ("Ex. 4") illustrates a configuration in which section 211 includes a combination of R and S1 materials and section 212 includes a combination of R and S2 materials, where the R materials in Example 4 may be the same or different. The same convention is used in Tables 2A and 2B. [Table 1] [Table 2] [Table 3]

[0063] The remaining examples in Tables 3, 4A, 4B, 4C, and 4D follow the same convention as Tables 1, 2A, and 2B. Table 3 shows eight examples of embodiments of the central region 210 having three sections 211, 212, and 213 and no shell 208, while Tables 4A, 4B, 4C, and 4D show 32 examples of embodiments having three sections 211, 212, and 213 and a shell 208. In these embodiments, the shell 208 can be the same material (S1, S2, or S3) as one of the sections 211, 212, and 213, or a different material (S4), with or without R material. If the same material is used, the shell 208 can be continuous (e.g., seamless) and integrated with the section (211, 212, or 213) having the same material. If shell 208 is integral with section 212, for example, shell 208 may surround or enclose all or substantially all of section 211 (or any combination of sections contained within shell structure 208), with beam axis 203 extending parallel to the wall of section 208 and then traversing section 208 / 212. Similarly, if shell 208 is integral with section 213, it may surround or enclose sections 211 and 212. [Table 4] [Table 5] [Table 6] [Table 7] [Table 8]

[0064] The S-materials (e.g., S1-S4) can include one or more that exhibit resonances within the energy range of neutrons generated by target 60 and beyond the desired output energy range, e.g., Fast-S materials if the desired energy range is epithermal. The S-materials can also include one or more NR-S materials that exhibit non-resonant properties within the energy range of neutrons generated by target 60 and beyond at least the desired output energy range, e.g., bridging the gap between Fast-S material resonances. In some exemplary embodiments, central region 210 includes a combination of at least one S-material that exhibits resonant properties and at least one S-material that exhibits non-resonant properties. These materials can be separated into different sections or combined into a single section (e.g., aluminum oxide). Table 5 shows eight examples of S-material configurations for an embodiment having two sections 211 (S1) and 212 (S2). Tables 6A and 6B show 14 example configurations of S material for an embodiment having three sections 211 (S1), 212 (S2) and 213 (S3). For example, referring to Example 1 of Table 5, S1 material includes both Fast-S material (indicated by an X in the F column) and NR-S material (indicated by an X in the NR column), while S2 material includes only Fast-S material (indicated by an X in the F column and an absence of an X in the NR column). The remaining examples use the same convention in Tables 5, 6A and 6B. The example configurations of Table 5 can be used with all two section examples of Tables 1, 2A and 2B, while the example configurations of Tables 6A and 6B can be used with all three section examples of Tables 3, 4A, 4B, 4C and 4D. [Table 9] [Table 10] [Table 11]

[0065] 14I-14N are cross-section vs. energy graphs illustrating the overall effect of combining multiple materials with different cross-section properties, and are just some of the many combinations of materials that can be used for sections 211, 212, and 213. FIG. 14I shows three materials that can be used as S1, S2, and S3 in any order: carbon (NR-S material), magnesium fluoride (Fast-S material), and aluminum (Fast-S material). FIG. 14J shows three materials that can be used as S1, S2, and S3 in any order: carbon (NR-S material), bismuth fluoride (Fast-S material and R material), and aluminum oxide (Fast-S material and NR-S material). FIG. 14K shows three materials, namely beryllium oxide (NR-S material), lead fluoride (Fast-S material and R material), and aluminum (Fast-S material), which can be used in any order as S1, S2, and S3. FIG. 14L shows three materials, namely beryllium oxide (NR-S material), magnesium fluoride (Fast-S material), and aluminum (Fast-S material), which can be used in any order as S1, S2, and S3. FIG. 14M shows three materials, namely ETFE (Fast-S material and NR-S material), lead fluoride (Fast-S material and R material), and aluminum (Fast-S material), which can be used in any order as S1, S2, and S3. FIG. 14N shows three materials. ETFE (Fast-S and NR-S materials), bismuth fluoride (Fast-S and R materials), and aluminum oxide (Fast-S and NR-S materials) can be used in any order as S1, S2, and S3. As can be seen from the graph, the combination of Fast-S and NR-S materials (such as beryllium or beryllium oxide) provides a more uniform cross-section over a wide energy range of high speed and epithermal energies.

[0066] In some embodiments, the upstream section 211 may include an S1 material having a scattering resonance cross section at a relatively high energy (e.g., high velocity) in the range of neutron energies generated by the target 60, the immediately downstream section 212 is an S2 material having one or more resonance cross sections at relatively low energies, and the most downstream section 213 is an S3 material having one or more resonance cross sections at or just above the desired energy range of the converted beam 70 (e.g., epithermal). Additionally or alternatively, sections 211, 212, and 213 may have resonant cross-sections at the same or similar energies, but with the upstream section 211 having a relatively largest cross-section at a relatively high energy (e.g., high velocity) within the range of neutron energies generated by the target 60 compared to the cross-sections of sections 212 and 213 at the same or similar high energies, the immediately downstream section 212 having a relatively largest cross-section at a relatively low energy compared to the cross-sections of sections 211 and 213 at the same or similar energies, and the most downstream section 213 having a relatively largest resonant cross-section at or just above the desired energy range of the converted beam 70 (e.g., epithermal).

[0067] The energy of these neutrons can be gradually decreased through each section so that the neutrons leaving the output section 202 are down-scattered into a desired range. Similarly, in some embodiments, the materials used in the various sections are selected to have resonance energies that do not completely overlap but at least partially complement each other to provide more uniform scattering. For example, magnesium fluoride and aluminum fluoride have resonances that only partially overlap at about 20 keV to 70 keV, as shown in Figures 14A, 14I, and 14L.

[0068] The R material can also provide benefits such as gamma radiation absorption. Placing the R material in the relatively more upstream sections (e.g., 211) allows more time and volume for other portions of the NBC 200 to redirect neutrons that are inadvertently redirected from section 211, since these neutrons can be redirected back to the central region 210 by the intermediate region 230. The downstream sections (e.g., 212, 213) can perform scattering without substantial redirection in order to maintain a forward-directed beam shape.

[0069] As a combination of R and S materials, lead fluoride has diverse capabilities due to the nuclear properties of lead and fluorine as well as multiple material properties. Fluorine atoms have a series of large resonant scattering peaks, amplified due to the high mass density of the compound, which preferentially scatters neutrons beyond the epithermal range without excessive energy loss (9.5% on average). Lead can serve two roles: as a reflector that only slightly changes the neutron energy spectrum until another fluorine atom is encountered, and as a photon shield that attenuates the prompt gamma rays generated in the NBC200. This material provides low neutron flux levels at the fluorine peak energies and higher neutron flux at the valley energies. Energy reduction of the valley flux can be achieved by alternating sections of lead fluoride with non-resonant materials such as beryllium or beryllium oxide. The thickness of the beryllium sections can be set corresponding to the amount of material that provides the appropriate number of collisions on average to advance neutrons from one fluorine resonance to the next. As shown in the above equation, beryllium is much more efficient in this process than lead or fluorine, and therefore the use of beryllium or beryllium oxide can reduce the overall size of central region 210.

[0070] The stacked sections within the central region 210 can be configured in numerous ways having different shapes, thicknesses, and combinations, as shown in the exemplary embodiments shown in cross-section in Figures 5A-5H. In these embodiments, the central region 210 is bisected along the beam axis 203 with the beam input 201 on the left and the beam output 202 on the right. Each central region 210 has interleaved sections 211 that vary in shape, size, and / or spacing relative to sections 212 in the same embodiment (e.g., Figures 5B, 5C, 5G) or in different embodiments (e.g., Figures 5A, 5D, 5E, 5F, 5H). The emphasis in Figures 5A-5H is on the various cross-sectional shapes and relative spacing of the layered sections, numerous combinations of which can be utilized, as opposed to the variability in materials and functionality within each group of sections (211, 212) and across different groups of sections (211, 212).

[0071] In the embodiment of FIG. 5A, each of the sections 211 has the same (or substantially the same) thickness (indicated by arrows 217) and each of the sections 212 has the same thickness (indicated by arrows 218). The thickness of the sections can be selected according to the needs of a particular beam transformation. For example, a thicker section with the ability to scatter at a particular resonance can achieve relatively more scattering as the thickness increases. In the embodiment of FIG. 5B, the thickness varies between the sections 211 and also between the sections 212. Here, the thickness 217 of the sections 211 gradually decreases from the input section 201 to the output section 202. The thickness 218 of the sections 212 can remain constant or gradually increase (as shown here). For example, in FIG. 5B, the effect produced by the sections 211 gradually decreases from the input section 201 to the output section 202, while the effect produced by the sections 212 gradually increases. FIG. 5C shows an embodiment in which the thickness 17 of section 211 remains constant and the thickness 218 of section 212 increases gradually from input portion 201 to output portion 202.

[0072] 5D illustrates an exemplary embodiment in which sections 211-1, 211-2, and 211-3 are each a grouping of multiple relatively thin materials. For example, each of sections 211 can include two, three (as shown here), four, or more of the same or different materials in thin sheets or plates arranged in contact. Each sheet can be a different material than the other sheets in that section 211, or the sheets can alternate between materials. In some embodiments, the sheets are of the same material arranged to facilitate construction of NBC 200 by allowing different sections 211 to be manufactured with different thicknesses determined by the number of sheets.

[0073] FIG. 5E shows an example embodiment in which section 211 has a curvilinear shape in cross-section, which may be bowl-shaped in three dimensions. The convex side of the bowl may face input 201 (as shown here) or the concave side of the bowl may face input 201 (i.e., inverted). FIG. 5F shows an example in which section 211 has a V-shaped or chevron-shaped cross-section, which may be conical when viewed in three dimensions. The relatively more pointed side may face input 201 (as shown here) or the concave side may face input 201 (i.e., inverted). The (axial) depth of each section may vary, as shown in the example of FIG. 5G. Here, section 211-1 has a relatively deep shape that becomes gradually shallower with sections 211-3 and 211-3 (e.g., the interior angle increases from section 211-1 to section 211-3). As with other embodiments, this configuration may be reversed. 5H shows an example where each section 211 has a variable radial thickness such that the thickness dimension is not constant when viewed across the cross section. Variable radial thickness may be applied in all of the embodiments shown or contemplated herein. A variable thickness, such as a thicker region centrally located along the beam axis, such as section 211, may have a greater effect on the material's ability to react to neutrons passing through that region. The variable thickness may be reversed with a thicker region off-center, such as section 212.

[0074] These embodiments are illustrative of the many different configurations that can be implemented, and the features of each embodiment can be combined with any and all features of the other embodiments.

[0075] Exemplary embodiments of the intermediate region 6A-6B are cross-sectional views illustrating an exemplary embodiment of the intermediate region 230. In FIG. 6A, the region 230 includes a first section 231 adjacent to and in contact with the lateral and upstream sides of the central region 210. The region 230 also includes a second section 232 adjacent to and in contact with the lateral and upstream sides of the section 231. The section 231 can function to scatter and redirect neutrons entering the section 231 from the central region 210 and / or the target 60. The scattering function can include reducing the energy of fast neutrons at large forward angles so that the neutrons are at an appropriate epithermal energy level when redirected back to the central region 230 and / or the beam output 202. Suitable materials for the section 231 can be, but are not limited to, any combination of S- and R-materials disclosed herein. Section 232 can function to redirect neutrons entering section 231 so that they can be scattered by section 232 and central region 210. Section 232 can also function as a photon shield. Neutrons passing through both sections 231 and 232 are scattered by section 231, allowing for easier absorption in peripheral region 250. Suitable materials for section 232 can include, but are not limited to, any of the R materials disclosed herein. In other embodiments, sections 231 and 232 can be made relatively thinner than those shown in FIG. 6A, and the sections can be repeated two or more times within middle region 230 (e.g., 231-232-231-232, etc.).

[0076] 4A-4K, redirection of neutrons into central region 210 by mid-region sections 231 and 232 results in those neutrons entering section 208. Section 208 may be composed of S material or other material that acts as a low resistance path for the propagation of neutrons from mid-region 230 to beam output 202. If central region 210 includes a section with R material, such as section 211 in the example of FIGS. 4A-4C, that material may help direct neutrons into shell 208, like a backstop for neutrons redirected from region 230.

[0077] In FIG. 6B, the middle region 230 again includes a layered arrangement of sections, each section adjacent to and surrounding the lateral and upstream lateral sides of the immediately preceding section. Section 231 is directly adjacent to the middle region 210 and can function as a neutron absorber, for example, using any of the Ab materials disclosed herein. Section 232 is the next upstream section and can function as a photon absorber, for example, using any of the R materials disclosed herein. Section 233 is the next upstream section and can function as an epithermal scattering section, for example, using any of the Epi-S materials disclosed herein. Section 234 is the next upstream section and can function as a neutron absorber, for example, using any of the Ab materials disclosed herein. Section 235 is the next upstream section and can function as a photon absorber, for example, using any of the R materials disclosed herein.

[0078] Exemplary embodiments of the peripheral region 7A-7B are cross-sectional views illustrating example embodiments of peripheral region 250. In both examples, region 250 includes a first section 251 adjacent to and in contact with the lateral and upstream sides of intermediate region 230. Region 250 also includes a second section 252 adjacent to and in contact with the lateral and upstream sides of section 251. Region 250 also includes a third section 253 adjacent to and in contact with the lateral and upstream sides of section 252.

[0079] In FIG. 7A, section 251 can function to scatter epithermal neutrons entering section 251 from intermediate region 230. This reduces the energy of the epithermal neutrons so that they are lower epithermal or thermal where they are more easily absorbed by section 252 configured as a neutron absorber. A suitable material for section 251 can be, for example, any of the Epi-S materials disclosed herein, and the material for section 252 can be, for example, any of the Ab materials disclosed herein. Section 253 can function as a photon shield to filter out remaining gamma radiation. A suitable material for section 232 can include any of the R materials disclosed herein. FIG. 7B is similar to FIG. 7A, except that section 251 is instead configured as a photon shield.

[0080] Exemplary embodiments of the front region 8A-8B are cross-sectional views illustrating an exemplary embodiment of the front region 270. The front region 270 can include more sections than those shown here, as well as sections of different types or functions. The front region can extend across the entire front surface of the NBC 200, except for the recess 205. In both examples, the region 270 includes a first section 271 that can form the front (e.g., the patient-facing portion) of the NBC 200. A second section 272 is located upstream of the section 271. The section 271 can function as a photon absorber and can be formed, for example, from any of the R materials disclosed herein. The section 272 can function as a neutron absorber and can be formed, for example, from any of the Ab materials disclosed herein. Together, the sections 271 and 272 filter or reduce the remaining photon and neutron radiation emitted from the front surface of the NBC 200 at locations around the desired beam output. In the embodiment of FIG. 8B, a third section 273 is located upstream of the section 272. Section 273 can function as an epithermal scattering section, for example made of any of the Epi-S materials disclosed herein, that acts to scatter epithermal neutrons downward to lower epithermal or thermal energy ranges where they are more easily absorbed by section 272.

[0081] In some embodiments, placing titanium-boron alloys or boron carbide in the front region 270 or in or near the beam output 202 or recess 206 substantially eliminates the low energy tail in the emitted neutron spectrum of the converted beam 70, thereby increasing the mean cosine theta of the beam 70 upon exit (e.g., pointing the neutrons more forward from the NBC 200). This is because the scattering laws dictate that as neutron energy increases, the most likely scattering angle goes from isotropic to more forward. Placement in the peripheral region for Epi-S and Ab functions is also advantageous, and Ti-B alloys such as titanium diboride and BC alloys such as boron carbide are highly formable, very hard ceramics and therefore can be made into special shapes for the NBC 200, such as the transition section described with respect to the embodiment of FIG. 12.

[0082] Further Exemplary Embodiments of the NBC 200 9A-9C are cross-sectional views showing exemplary embodiments of the NBC 200 in a first configuration. These embodiments have similar structures, the only difference being the display of the central region 210. Each of the embodiments has a middle region having two sections 231 and 232, which can be configured according to the embodiments of the middle region 230 described herein. Each of the embodiments also has a peripheral region having three sections 251, 252, and 253, which can be configured according to the embodiments of the peripheral region 250 described herein. The front region 270 is shown here as a combination of two sections 271, 272, which can be configured according to the embodiments of the front region 270 described herein. The central region 210 is shown here in a generic form and can implement any of the embodiments of the central region 210 described herein, including each of the embodiments of FIGS. 4A-4K. The section 252 of the peripheral region extends downstream of the sections 251, 232, 231, and over a portion of the central region 210 to a location between these components and the front region 270. When configured as a neutron absorber, section 252 can act to provide additional absorption benefits over the front side of NBC 200 and locations where neutron emissions are not desired.

[0083] In the embodiment of Figure 9B, the central region 210 includes a shell 208 that surrounds the layered region in an arrangement similar to that described with respect to Figure 4I. The layered region includes a series of six layers of a combination of R and S1 materials (R+S1), indicated by cross-hatching, with six layers of S2 material interspersed therein and thereover.

[0084] In the embodiment of Figure 9C, the central region 210 includes a shell 208 carrying multiple scattering sections similar to those described with respect to Figure 4E. The shell 208 is constructed of S1 material that spans the target assembly 65. A first section 211 is constructed of S2 material and a second section 212, downstream of section 211, is constructed of S3 material.

[0085] Table 7 shows ten examples of material combinations that can be used for the embodiments of Figures 9B and 9C. In these ten examples, the central region has three sections 211, 212, and 213, and the shell 208 has an integral composition with section 213. These examples are not intended to be exhaustive of all possible configurations of the embodiments of Figures 9B and 9C, as other materials and configurations are described herein. [Table 12-1] [Table 12-2]

[0086] 10A-10C are cross-sectional views illustrating an exemplary embodiment of NBC 200 in a second configuration. The embodiments have similar construction, the only difference being the display of central region 210. Each of the embodiments has a middle region having two sections 231 and 232 and a third section 233 interposed therebetween. Sections 231 and 232 may be configured according to the embodiments of middle region 230 described herein. Section 233 may be configured as a containment vessel that works with other components to maintain the position of sections 231 and / or 232 in place. Such a vessel may be desirable when the material forming sections 231 and / or 232 is in powder form. If necessary, a similar liner (not shown) may be placed between sections 231 and 208. Each of the embodiments also has a peripheral region having three sections 251, 252, and 253 that may be configured according to the embodiments of peripheral region 250 described herein. An optional fourth section 254 may be inserted between sections 251 and 252 and may function, for example, for further neutron absorption. Sections 252 and 253 may wrap around the front of NBC 200 and function as front region 270. Section 253 may form a flange or lip that continues along the inner surface of recess 205 and act as a neutron redirector at that location. Central region 210 is shown in a generic form here and any of the embodiments of central region 210 described herein may be implemented herein, including each of the embodiments of FIGS. 4A-4K.

[0087] In the embodiment of FIG. 10B, the central region 210 includes a shell 208 surrounding the layered region in a similar arrangement as described with respect to FIG. 4G. The layered region includes a series of four sections 211, shown cross-hatched, with three layers of section 212 interposed therein. The shell 208 may be formed of the same material as the third section 213 to make these portions continuous. Two layers of section 212 are included within section 213 downstream of the other layered sections. Also in this embodiment, a liner 209 is present around the recess 205. The liner 209 may be composed of a redirector material or a scattering material.

[0088] In the embodiment of Figure 10C, central region 210 includes a shell 208 carrying multiple scattering sections similar to those described with respect to Figure 4E. Shell 208 is constructed from the same material as section 211. Section 212 is located downstream of section 211, and section 213 is located downstream of section 212.

[0089] 11A-11C are cross-sectional views illustrating an exemplary embodiment of the NBC 200 in a third configuration. These embodiments have similar constructions, the only difference being the display of the central region 210. Each of the embodiments has a middle region having two sections 231 and 232 that may be configured according to the embodiments of the middle region 230 described herein. Each of the embodiments also has a peripheral region having three sections 251, 252, and 253 that may be configured according to the embodiments of the peripheral region 250 described herein. In this embodiment, section 251 has a non-uniform lateral dimension with an outermost surface that extends laterally outward at an axial location aligned with the target 60. The inner surface of section 251 has a constant lateral dimension. A fourth section 254 is located around the outer side of section 251 and may function, for example, for additional neutron absorption. Sections 252 and 253 wrap around the front of the NBC 200 and may function as part of the front region 270. Section 251 can also continue through the front region at an oblique angle to axis 203 and in a discontinuous configuration separated from the remainder of section 251 by plate-like portions of sections 252 and 253. Section 254 can also continue through the front region at an oblique angle to axis 203 across oblique section 252 and also in a discontinuous configuration separated from the remainder of section 254 by plate-like portions of sections 251 and 253. Central region 210 is shown here in a generic form and any of the embodiments of central region 210 described herein may be implemented herein, including each of the embodiments of Figures 4A-4K.

[0090] In the embodiment of FIG. 11B, the central region 210 includes a shell 208 surrounding the layered region in a similar arrangement as described with respect to FIG. 4G. The layered region includes a series of four sections 211, shown cross-hatched, with three layers of section 212 interposed therein. The shell 208 may be formed of the same material as the third section 213 to make these portions continuous. Two layers of section 212 are included within section 213 downstream of the other layered sections. Also in this embodiment, a liner 209 is present around the recess 205. The liner 209 may be composed of a redirector material or a scattering material.

[0091] In the embodiment of Figure 11C, central region 210 includes a shell 208 carrying multiple scattering sections similar to those described with respect to Figure 4E. Shell 208 is constructed of S1 material that spans target assembly 65. Shell 208 is constructed of the same material as section 211. Section 212 is located downstream from section 211, and section 213 is located downstream from section 212.

[0092] Table 8 shows ten examples of material combinations that can be used for the embodiments of Figures 10B, 10C, 11B, and 11C. In these ten examples, the central region has three sections 211, 212, and 213, and the shell 208 has an integral composition with section 213. These examples are not intended to be exhaustive of all possible configurations of the embodiments of Figures 10B, 10C, 11B, and 11C, as other materials and configurations are described herein. [Table 13-1] [Table 13-2]

[0093] Exemplary embodiments having cylindrical and / or non-cylindrical surfaces Certain materials exhibit excellent properties for use in conditioning and shielding neutron beams while at the same time being moldable to facilitate construction of the NBC 200 and surrounding support structures. For example, the previously described embodiments of the NBC 200 having various regions and sections that are cylindrical or substantially cylindrical (e.g., cylindrical around the beam) have curved outer surfaces that may be prone to roll, shift, or otherwise not as convenient to work with and install as flat surfaces. FIG. 12 is a perspective view illustrating an exemplary embodiment of the NBC 200 similar to the embodiment of FIG. 3A, in which the outermost surface of the peripheral region 250 is in the shape of a multi-sided flat surface, such as a right angle prism or cube. The section of the peripheral region 250 can be configured to have a lateral inner surface having a curved or at least partially cylindrical shape that corresponds to the lateral outer curved or at least partially cylindrical surface of the intermediate region 230. The interior section can be configured to have a lateral outer surface having a multi-sided flat surface shape and thus can be used to transition the section of the NBC 200 from being substantially cylindrical to having a flat surface.

[0094] This transition can be performed using any of the sections of the peripheral region 250, including the innermost section (e.g., section 251), the outermost section (e.g., section 253), and sections located therebetween (e.g., sections 252 and 254). The transition is facilitated when the transition sections are constructed from a material that can be easily molded, cast, machined, and / or 3D printed. Examples of such materials are ceramic titanium diboride, ceramic boron carbide, polyethylene (PE) (e.g., boron doped polyethylene of section 254), and polymers such as ETFE. The material of the sections located outside the transition sections can be constructed as blocks or plates without significant curved surfaces that are then relatively easy to manufacture and assemble into the complete structure of the NBC 200.

[0095] FIG. 13 is a perspective view of another exemplary embodiment of an NBC 200 similar to the embodiment of FIGS. 9A-10C, having a central region 210, an inner intermediate liner 233-1, an intermediate section 231, an outer intermediate liner 233-2, an intermediate section 232, and peripheral sections 251, 252, and 253. Here, the intermediate liner 233-3 is a transition section between a generally curved laterally outer side or shape and an inner side or shape having multiple sides. The innermost surface (interior) of the intermediate liner 233-2 can have a curvature or radius that corresponds to (e.g., matches) the curvature or radius of the outer surface of the intermediate section 231. The outermost surface (exterior) of the intermediate liner 233-2 can be a polygonal surface that matches the innermost surface of the intermediate section 232. In the illustrated embodiment, region 210 and sections 231-1 and 231-2 within liner 233-2 have a generally cylindrical shape, while section 232 and sections 251, 252, and 253 of peripheral region 250 have a generally polygonal surface. As with the embodiment of FIG. 12, this configuration allows for an optimal shape (e.g., cylindrical) for neutron conversion in the innermost volume of NBC 200, while transitioning to a polygonal surface configuration in the outermost volume of NBC 200 where neutron conversion requires less symmetry and ease of assembly, manufacturing, and maintenance are less of a concern. While shown here as a polygon with eight sides or flanks, in other embodiments the polygon can have four, five, six, seven, nine, ten, or more sides, as well as at least two end faces (at least one corresponding to the most upstream location and at least one corresponding to the most downstream location).

[0096] The lateral sides or shapes of the cylinders and polygons need not be perfect geometric cylinders or polygons. Those skilled in the art will recognize upon reading this description that such sides or shapes can be substantially cylindrical or polygonal, and those skilled in the art will readily recognize sides or shapes that are substantially cylindrical or polygonal. For example, some flatness can be present on the lateral cylindrical sides or shapes, which flatness has a negligible effect on the overall neutron beam profile output from the beam output. Similarly, some rounding or curvature can be present on the lateral polygonal sides or shapes, which rounding or curvature also has a negligible effect on the overall neutron beam profile output from the beam output. In some embodiments, the substantially cylindrical shapes vary from the geometric cylinder by no more than 5% of the overall lateral dimension. In some embodiments, the substantially polygonal shapes vary from the corresponding geometric polygon by no more than 5% of the overall lateral dimension.

[0097] The NBC 200, including the sections of regions 210, 230, 250, and 270, can be manufactured according to a process that provides a desired balance between manufacturability, performance, and cost. Portions of the NBC 200 that make up one of the sections of regions 210, 230, 250, and 270 can be manufactured separately and then assembled to form a larger section or even larger region. The material of the NBC 200 can be in a continuous solid form (e.g., a sheet of lead). A combination of first and second materials, such as R and S materials or different types of S materials (e.g., Fast-S and NR-S materials), can be in the form of a bonded compound. The base and composite materials can be in the form of raw material granules or powders and then set into a desired shape by casting, molding, sintering, or mixing with additives (e.g., adhesives such as epoxy or enamel blends, etc.). The material can also be in granular or powder form and can be maintained or held in the desired shape using a metal housing or casement.

[0098] Various aspects of the present subject matter are described below in consideration of and / or in supplement to the previously described embodiments, with emphasis on the interrelationships and compatibility of the following embodiments and their aspects. In other words, emphasis is placed on the fact that each aspect of the embodiments can be combined with any and all other aspects, unless expressly stated or taught otherwise.

[0099] In a first group of embodiments, a neutron beam converter is provided, the converter including: a beam input configured to receive neutrons from a neutron generating target; a beam output configured to output neutrons; a central region transected by an axis between the beam input and the beam output, the central region configured to scatter neutrons into a therapeutic energy range; an intermediate region positioned laterally around the central region and configured to redirect and scatter neutrons, the intermediate region including first and second intermediate sections each comprising a different material; and a peripheral region positioned laterally around the intermediate region and configured to absorb neutrons and gamma radiation, the peripheral region including first and second peripheral sections each comprising a different material.

[0100] In some embodiments of the first group, the central region can include a first section, a second section, and a third section, each of the first, second, and third sections including a different material, each of the first, second, and third sections being traversed by an axis, The first section can include fluorine, the second section can include magnesium, and the third section can include aluminum.

[0101] In some embodiments of the first group, the central region can include a first material and a second material. The first material can include aluminum and the second material can include magnesium. The first material can be configured to scatter generated neutrons toward or into a therapeutic energy range and can be configured to redirect the generated neutrons, and the second material can be configured to non-resonantly scatter the generated neutrons. The first material can include lead and fluorine. The second material can include beryllium. The second material can include at least one of an oxide, a carbide, or a nitride. The second material can be configured as a layer between a first central section including the first material and a second central section including the first material. The first central section, the layer, and the second central section can be traversed by an axis. The central region can include a third material including at least one of aluminum, fluorine, and magnesium.

[0102] In some embodiments of the first group, the central region may include a cylindrical portion extending from the beam input to the beam output. The cylindrical portion may have a first end upstream of a location of the neutron generating target. The cylindrical portion may have a first end along a most upstream face of the neutron beam converter. The cylindrical portion may have a second end proximate to the beam output. The cylindrical portion may be configured to act as a low resistance path for neutrons relative to the intermediate region. The cylindrical portion may include a tubular portion. The cylindrical portion may be configured to act as a low resistance path for neutrons relative to a material within the intermediate region and the tubular portion. The tubular portion may include at least one of aluminum, fluorine, and magnesium and laterally surrounds the first central section including the first material and the second material. The cylindrical portion may include at least one of aluminum, fluorine, and magnesium. The cylindrical portion may traverse the axis.

[0103] In some embodiments of the first group, the converter can have a downstream-most surface and a recess from the downstream-most surface at the beam output. The recess can have a sidewall portion including a neutron redirector. The neutron redirector can include at least one of lead, nickel, bismuth, and tungsten. The recess can be cylindrical and the converter can include a tubular liner including beryllium, the tubular liner can be located proximate a sidewall of the recess.

[0104] In some embodiments of the first group, the central region can include a first central section traversed by the axis and configured to scatter neutrons into a therapeutic energy range, a second central section traversed by the axis and located downstream of the first central section and configured to scatter neutrons in the epithermal energy range to lower energies, and a third central section traversed by the axis and located downstream of the second central section and configured to absorb neutrons scattered to lower energies.

[0105] In some embodiments of the first group, the central region can include a solid section spaced apart from the neutron generating target location, the solid section can be traversed by the access and can be located downstream of the target location, and the solid section can be spaced apart from the target location by at least 10 centimeters.

[0106] In some embodiments of the first group, the first intermediate section may be relatively closer to the central region than the second intermediate section, and the first intermediate section may be configured to scatter the generated neutrons and the second intermediate section may be configured to redirect the generated neutrons. The second intermediate section may be configured to redirect the generated neutrons and absorb photons. The first intermediate section may be further configured to redirect the neutrons. The first intermediate section may include at least one of fluorine, aluminum, and magnesium, and the second intermediate section may include at least one of lead, nickel, bismuth, and tungsten. The first intermediate section may include lead, and the second intermediate section may include lead.

[0107] In some embodiments of the first group, the first intermediate section can be located laterally about the central region and the second intermediate section can be located laterally about the first intermediate section. The first intermediate section can be in contact with the central region and the second intermediate section can be in contact with the first intermediate section.

[0108] In some embodiments of the first group, the intermediate region can extend laterally across the posterior surface of the central region.

[0109] In some embodiments of the first group, the second intermediate section can be located laterally around the first intermediate section, the first intermediate section can be configured to scatter neutrons, and the second intermediate section can be configured to redirect neutrons and absorb gamma radiation. The intermediate region can include a third intermediate section located laterally around the second intermediate section, the third intermediate section can be configured to scatter neutrons from a first energy in the epithermal energy range to a second energy lower than the first energy. The intermediate region can include a fourth intermediate section located laterally around the third intermediate section, the fourth intermediate section can be configured to absorb neutrons. The intermediate region can include a fifth intermediate section located laterally around the fourth intermediate section, the fifth intermediate section can be configured to absorb gamma radiation.

[0110] In some embodiments of the first group, the first peripheral section may be relatively closer to the middle region than the second peripheral section, and the first peripheral section may be configured to absorb neutrons, and the second peripheral section may be configured to absorb photons. The peripheral region may include a third peripheral section located relatively closer to the middle section than the first peripheral section, and the third peripheral section may be configured to scatter epithermal neutrons. The peripheral region may include a third peripheral section located relatively closer to the middle section than the first peripheral section, and the third peripheral section may be configured to absorb photons. The first and second peripheral sections may include titanium. The first peripheral section may include titanium and vanadium. The second peripheral section may include boron. The first peripheral section may be located laterally around the middle and central regions, and the second peripheral section may be located laterally around the first peripheral section. The first peripheral section can contact the intermediate region and the second peripheral section can contact the first peripheral section. The peripheral region can extend laterally across a portion of the rear of the central region and a portion of the rear of the intermediate region.

[0111] In some embodiments of the first group, the converter includes a front region extending laterally across the converter. The front region may be configured to absorb neutrons and photons. The front region may include a first front section configured to absorb photons and a second front section configured to absorb neutrons. The first front section may be located downstream of the second front section. The first front section may include an opening for a recess in the beam output. The first front section may include at least one of lead, nickel, bismuth, and tungsten. The second front section may include at least one of lithium, cadmium, boron, titanium, gadolinium, indium, hafnium, and hydrogen polymer. The converter may include a third front section configured to scatter epithermal neutrons. The third front section may be located upstream of the second front section. The front region may form a continuation of the peripheral region.

[0112] In a second group of embodiments, a neutron beam converter is provided that includes a beam input configured to receive neutrons, a beam output configured to output neutrons, a first region intersected by an axis between the beam input and the beam output, and a second region positioned laterally about the first region, the second region including an alloy including titanium and vanadium.

[0113] In some embodiments of the second group, the second region can include a first section including the alloy and a second section including boron. The first section can be located laterally around the first region, and the second section can be located laterally around the first section. The converter can include a third region interposed between the first region and the second region, the first region being a central region, the third region being an intermediate region, and the second region being a peripheral region. The second region can include lead. The second region can include a hydrogen polymer.

[0114] In a third group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons, a beam output configured to output neutrons, a first region intersected by an axis between the beam input and the beam output, and a second region located laterally around the first region or along a front region proximate to the treatment chamber, the second region including boron.

[0115] In some embodiments of the third group, the second region can include a first section including an alloy of titanium and vanadium and a second section including boron. The first section can be located laterally around the first region and the second section can be located laterally around the first section. The transducer can include a third region interposed between the first region and the second region, the first region being a central region, the third region being a middle region, and the second region being a peripheral region. The boron can be ceramic titanium diboride or ceramic boron carbide.

[0116] In some embodiments of the third group, the second region comprises a hydrogen polymer.

[0117] In some embodiments of the third group, the transducer includes a front surface region having boron, the front surface region being located across a downstream front surface of the transducer.

[0118] In some embodiments of the third group, the second region exhibits an inverse velocity cross section over at least a portion of the thermal neutron energy range and the epithermal neutron energy range.

[0119] In some embodiments of the third group, the second region exhibits a resonant peak cross section in the epithermal neutron energy range.

[0120] In some embodiments of the third group, the second region is located laterally around the first region.

[0121] In some embodiments of the third group, the second region is located along the front region.

[0122] In a fourth group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons, a beam output configured to output neutrons, and a central region traversed by an axis between the beam input and the beam output, the central region including a plurality of first sections and a plurality of second sections, the plurality of first sections traversed by the axis and configured to resonantly down-scatter neutrons, and the plurality of second sections traversed by the axis and configured to non-resonantly down-scatter neutrons.

[0123] In some embodiments of the fourth group, the plurality of first sections and the plurality of second sections are in an alternating stacked arrangement.

[0124] In some embodiments of the fourth group, the plurality of second sections can include beryllium.

[0125] In some embodiments of the fourth group, the plurality of first sections can include at least one of magnesium, aluminum, and fluorine.

[0126] In some embodiments of the fourth group, the plurality of first sections can include lead and fluorine.

[0127] In some embodiments of the fourth group, the transducer can include a plurality of third sections traversed by the axis and configured to resonantly down-scatter neutrons, and the plurality of first sections include a different material than the plurality of third sections. At least a portion of the plurality of second sections and the plurality of third sections can be in an alternating stacked arrangement.

[0128] In some embodiments of the fourth group, the converter is traversed by the axis and includes a plurality of third sections configured to resonantly down-scatter neutrons, the plurality of first sections are interleaved with the plurality of second sections and the plurality of third sections, the plurality of first sections include at least one of magnesium, aluminum, or fluorine, the plurality of second sections include beryllium, and the plurality of third sections include a material including lead and fluorine.

[0129] In some embodiments of the fourth group, the plurality of first sections may be contiguous.

[0130] In a fifth group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons, a beam output configured to output neutrons, a central region between the beam input and the beam output, an intermediate region located laterally around the central region, and a peripheral region located laterally around the intermediate and central regions, the central region including a first material comprising lead and fluorine, the first material being traversed by an axis between the beam input and the beam output, the intermediate region including a second material comprising lead and fluorine, and a third material located between the first material of the central region and the second material of the intermediate region.

[0131] In some embodiments of the fifth group, the first and second materials are the same.

[0132] In some embodiments of the fifth group, the first and second materials may be lead fluoride.

[0133] In some embodiments of the fifth group, the third material may include at least one of magnesium and aluminum.

[0134] In some embodiments of the fifth group, the third material can be a magnesium-aluminum alloy.

[0135] In some embodiments of the fifth group, the intermediate region includes a first section having a second material and a second section having a fourth material including at least one of lead, nickel, bismuth, and tungsten. The second section can be positioned laterally about the first section.

[0136] In some embodiments of the fifth group, the peripheral region can include at least one of lead, nickel, bismuth, and tungsten.

[0137] In a sixth group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons from a neutron generating target, a beam output configured to output neutrons, and a central region between the beam input and the beam output, the central region including at least one section comprising beryllium.

[0138] In some embodiments of the sixth group, the section containing beryllium is separated from the beam input by another material.

[0139] In some embodiments of the sixth group, at least one section is configured as a plate, and a central axis of the transducer extending from the beam input to the beam output is perpendicular to the plate.

[0140] In some embodiments of the sixth group, the at least one section is one of a plurality of first sections spaced apart between the beam input section and the beam output section, and each of the plurality of first sections comprises beryllium.

[0141] In some embodiments of the sixth group, each adjacent pair of first sections in the plurality of first sections is separated by one of the plurality of second sections, each of the plurality of second sections may be configured to resonantly scatter neutrons to lower energies.

[0142] In some embodiments of the sixth group, the plurality of first sections can be configured as a plate, and a central axis of the converter extending from the beam input section to the beam output section is perpendicular to each first section of the plurality of first sections.

[0143] In some embodiments of the sixth group, at least one section can include beryllium oxide.

[0144] In some embodiments of the sixth group, at least one section may be configured to non-resonantly down-scatter neutrons to lower energies.

[0145] In a seventh group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons from a neutron generating target, a beam output configured to output neutrons, a first region between the beam input and the beam output, and a second region located laterally around the first region, the second region including a first section having an outer diameter that varies along a length of the first section.

[0146] In some embodiments of the seventh group, the first section has a maximum diameter at a first location aligned with the neutron generating target location. The diameter of the first section can decrease from the first location to a second location at a downstream end of the first section. The diameter of the first section can decrease from the first location to a second location at an upstream end of the first section.

[0147] In some embodiments of the seventh group, the first region is a central region, the second region is a peripheral region, and the transducer includes an intermediate region between the central region and the peripheral region.

[0148] In some embodiments of the seventh group, the inner surface of the first section has a cylindrical shape with a uniform diameter.

[0149] In some embodiments of the seventh group, the first section may be configured to downwardly scatter epithermal neutrons.

[0150] In some embodiments of the seventh group, the first section can include titanium.

[0151] In some embodiments of the seventh group, the second region can have a cylindrical outer surface of uniform diameter.

[0152] In some embodiments of the seventh group, the second region includes a second section positioned laterally about the first section, the second section having an inner diameter that varies corresponding to an outer diameter of the first section. The second section can have a uniform outer diameter along a length of the second section.

[0153] In an eighth group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons, a beam output configured to output neutrons, and a central region between the beam input and beam output, the central region including a plurality of first sections in an alternating stacked arrangement with a plurality of second sections, the first section of the plurality of first sections having a thickness relatively smaller than a thickness of a second section of the plurality of first sections.

[0154] In some embodiments of the eighth group, each of the plurality of first sections can have a different thickness.

[0155] In some embodiments of the eighth group, a thickness of a first section of the plurality of first sections is at least 10% less than a thickness of a second section of the plurality of first sections.

[0156] In some embodiments of the eighth group, a first section of the plurality of first sections can be located relatively closer to the beam output than a second section of the plurality of first sections.

[0157] In some embodiments of the eighth group, a first section of the plurality of first sections can be located relatively farther from the beam output section than a second section of the plurality of first sections.

[0158] In some embodiments of the eighth group, a thickness of the plurality of first sections may gradually decrease in a direction from upstream to downstream.

[0159] In some embodiments of the eighth group, a thickness of the plurality of first sections may increase gradually in the upstream-to-downstream direction.

[0160] In some embodiments of the eighth group, the plurality of first sections can have a different composition than the plurality of second sections.

[0161] In some embodiments of the eighth group, each of the plurality of first sections may be configured as a plate.

[0162] In some embodiments of the eighth group, each of the plurality of first sections may be configured to non-resonantly scatter neutrons and each of the plurality of second sections may be configured to resonantly scatter neutrons.

[0163] In some embodiments of the eighth group, each of the plurality of first sections may be configured to resonantly scatter neutrons and each of the plurality of second sections may be configured to non-resonantly scatter neutrons.

[0164] In some embodiments of the eighth group, all of the plurality of second sections can have the same thickness.

[0165] In some embodiments of the eighth group, each of the plurality of second sections may be thicker than each of the plurality of first sections.

[0166] In a ninth group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons, a beam output configured to output neutrons, and a central region between the beam input and beam output, the central region including a plurality of first sections interleaved with a plurality of second sections, the plurality of first sections including non-planar first sections.

[0167] In some embodiments of the ninth group, the non-planar first section can have a chevron-shaped cross-sectional profile. The chevron-shaped cross-sectional profile can have an open side and a relatively pointed side, the relatively pointed side facing the beam input. The chevron-shaped cross-sectional profile can have an open side and a relatively pointed side, the relatively pointed side facing the beam output.

[0168] In some embodiments of the ninth group, each of the plurality of first sections can have a cross-sectional profile that is chevron shaped.

[0169] In some embodiments of the ninth group, the non-planar first section can have a curved cross-sectional profile. The curved cross-sectional profile can have a concave side and a convex side, the convex side facing the beam input. The curved cross-sectional profile can have a concave side and a convex side, the concave side facing the beam input.

[0170] In some embodiments of the ninth group, each of the plurality of first sections can have a curved cross-sectional profile.

[0171] In some embodiments of the ninth group, the non-planar first section may be bowl-shaped.

[0172] In some embodiments of the ninth group, the non-planar first section can have a cross-sectional profile with a non-uniform thickness.

[0173] In some embodiments of the ninth group, the non-planar first section can have a curved cross-sectional profile, and the plurality of first sections can include a chevron-shaped first section.

[0174] In a tenth group of embodiments, a neutron beam converter is provided, the converter including a beam input configured to receive neutrons from a neutron generating target, a beam output configured to output neutrons, a first region or section between the beam input and the beam output, the first region or section having a first lateral outer surface curved about an axis between the beam input and the beam output, and a second region or section positioned laterally around the first region or section, the second region or section having a second lateral outer surface that is substantially multi-faceted.

[0175] In some embodiments of the tenth group, the first laterally outer surface may be substantially cylindrical or cylindrical.

[0176] In some embodiments of the tenth group, the first region or section may be a first section of a central region of the transducer, and the second region or section may be a second section of a central region of the transducer.

[0177] In some embodiments of the tenth group, the first region or section may be a central region of the converter. The second region or section is a section of a middle region of the converter. The second region or section is a middle region of the converter. The middle region may be configured to redirect and scatter generated neutrons.

[0178] In some embodiments of the tenth group, the second region or section may be a section of a peripheral region of the transducer, the transducer including an intermediate region located between the central region and the peripheral region.

[0179] In some embodiments of the tenth group, the second region or section may be a peripheral region of the transducer, the transducer including an intermediate region located between the central region and the peripheral region.

[0180] In some embodiments of the tenth group, the central region can be configured to scatter generated neutrons towards or into a therapeutic energy range.

[0181] In some embodiments of the tenth group, the second lateral outer surface can have four or more lateral sides and at least two end sides.

[0182] In some embodiments of the tenth group, the second lateral outer surface can have six or more lateral sides and at least two end sides.

[0183] In some embodiments of the tenth group, the second region or section can include a laterally inner portion having a curvature corresponding to the first laterally outer portion.

[0184] In some embodiments of the tenth group, the transducer includes two or more first sections in a central region, each of the two or more first sections having a lateral outer portion that is curved about an axis between the beam input section and the beam output section, and two or more second sections in an intermediate region and / or peripheral region of the transducer, each of the two or more second sections having a lateral outer portion that is substantially multi-sided about the axis.

[0185] In the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth groups of embodiments, the converter may be configured to output a neutron beam from the beam output within the epithermal energy range.

[0186] In the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth groups of embodiments, the converter may be configured to output a neutron beam in the energy range of 1 electron volt to 30 kiloelectron volts. The converter may be configured to output a neutron beam having a peak neutron distribution and an average energy of 10 kiloelectron volts to 30 kiloelectron volts. The converter may be configured to output a neutron beam with at least 90% of the neutrons in the energy range of 1 electron volt to 30 kiloelectron volts.

[0187] In the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth groups of embodiments, the converter may be configured to output a neutron beam in the energy range of 1 electron volt to 10 kiloelectron volts. The converter may be configured to output a neutron beam having a peak neutron distribution and an average energy of 3 kiloelectron volts to 10 kiloelectron volts. The converter may be configured to output a neutron beam with at least 90% of the neutrons in the energy range of 1 electron volt to 10 kiloelectron volts.

[0188] In the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth groups of embodiments, the converter may be configured for use in a boron neutron capture therapy system.

[0189] In the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth groups of embodiments, the converter may include a neutron generating target. The neutron generating target may include lithium and may be configured to generate neutrons according to the reaction p+7Li→n+7Be. The neutron generating target may be configured to generate neutrons from a proton beam having an energy in the range of 1.9 to 3.0 megaelectron volts.

[0190] In the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth groups of embodiments, the converter may be configured to receive an unprocessed neutron beam from the neutron generating target and output a converted neutron beam, the converted neutron beam having a relatively more focused forward direction than the unprocessed neutron beam, a relatively smaller variation in intensity than the unprocessed neutron beam, and a relatively smaller variation in energy than the unprocessed neutron beam.

[0191] In an eleventh group of embodiments, a method of converting a neutron beam is provided, the method comprising propagating a charged particle beam at a neutron generating target located within a neutron beam converter such that a neutron beam is emitted from a neutron beam output of the neutron beam converter, the neutron beam converter being configured according to any of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth group of embodiments.

[0192] In a twelfth group of embodiments, a method of treating a patient with Boron Neutron Capture Therapy (BNCT) is provided, the method including propagating a neutron beam in the patient, the neutron beam being emitted from a neutron beam output of a neutron beam converter, the neutron beam converter being configured according to any of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth group of embodiments.

[0193] To the extent that the embodiments disclosed herein include or operate in conjunction with memory, storage, and / or computer-readable medium, the memory, storage, and / or computer-readable medium are non-transitory. Thus, to the extent that the memory, storage, and / or computer-readable medium is encompassed by one or more claims, the memory, storage, and / or computer-readable medium is only non-transitory.

[0194] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0195] While the embodiments are susceptible to various modifications and alternative forms, specific examples thereof are shown in the drawings and described in detail herein. It is to be understood, however, that these embodiments are not limited to the particular forms disclosed, but on the contrary, these embodiments are intended to encompass all modifications, equivalents, and alternatives falling within the spirit of the present disclosure. Furthermore, negative limitations may be written into or added to the claims that define the scope of the claimed invention by any feature, function, step, or element of the embodiments, as well as features, functions, steps, or elements not within their scope.

Claims

1. 1. A neutron beam converter comprising: a beam input configured to receive neutrons from a neutron generating target; a beam output configured to output neutrons; a central region intersected by an axis between the beam input and the beam output, the central region being configured to scatter neutrons into a therapeutic energy range; and an intermediate region positioned laterally about the central region and configured to redirect and scatter neutrons, the intermediate region including a first intermediate section and a second intermediate section, each of the first intermediate section and the second intermediate section comprising a different material; a peripheral region positioned laterally around the intermediate region and configured to absorb neutron and gamma radiation, the peripheral region including a first peripheral section and a second peripheral section, each of the first peripheral section and the second peripheral section comprising a different material.

2. 2. The transducer of claim 1, wherein the central region comprises a first section, a second section, and a third section, each of the first, second, and third sections comprising a different material, each of the first, second, and third sections intersected by the axis, and optionally, the first section comprises fluorine, the second section comprises magnesium, and the third section comprises aluminum.

3. 2. The converter of claim 1, wherein the central region comprises a first material and a second material, optionally wherein the first material comprises aluminum and the second material comprises magnesium, or wherein the first material is configured to scatter generated neutrons toward or into a therapeutic energy range and is configured to redirect generated neutrons, and the second material is configured to non-resonantly scatter generated neutrons.

4. 4. The converter of claim 3, wherein the first material comprises lead and fluorine, or the second material comprises beryllium, or at least one of an oxide, a carbide, or a nitride.

5. The transducer of claim 3 , wherein the second material is configured as a layer between a first central section comprising the first material and a second central section comprising the first material.

6. The transducer of claim 5 , wherein the first central section, the layer, and the second central section are intersected by the axis.

7. The transducer of claim 3 , wherein the central region includes a third material including at least one of aluminum, fluorine, and magnesium.

8. 2. The converter of claim 1, wherein the central region includes a cylindrical portion extending from the beam input to the beam output, and optionally the cylindrical portion has a first terminus upstream of a location of the neutron generating target or along a most upstream face of the neutron beam converter.

9. 9. The transducer of claim 8, wherein the cylindrical portion has a second end proximate the beam output.

10. 9. The converter of claim 8, wherein the cylindrical portion is configured to act as one of a low resistance path for neutrons relative to the intermediate region or a low resistance path for neutrons relative to material within the intermediate region and the tubular portion.

11. The transducer of claim 8 , wherein the cylindrical portion comprises a tubular portion.

12. The transducer of claim 11 , wherein the tubular portion comprises at least one of aluminum, fluorine, and magnesium and laterally surrounds a first central section comprising a first material and a second material.

13. 9. The converter of claim 8, wherein the cylindrical portion comprises at least one of aluminum, fluorine, and magnesium, optionally the cylindrical portion transverses the axis, and optionally the converter has a downstream-most surface and a recess from the downstream-most surface at the beam output portion.

14. 14. The converter of claim 13, wherein the recess has a sidewall portion including a neutron redirector, optionally the neutron redirector including at least one of lead, nickel, bismuth, and tungsten, and optionally the recess is cylindrical, and the converter includes a tubular liner including beryllium, the tubular liner located adjacent a sidewall of the recess.

15. The central region is a first central section intersected by the axis and configured to scatter neutrons into the treatment energy range; a second central section traversed by the axis and located downstream of the first central section, the second central section configured to scatter neutrons within the epithermal energy range to lower energies; a third central section traversed by the axis and located downstream of the second central section, the third central section configured to absorb the lower energy scattered neutrons.

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