Efficient Bremsstrahlung Converter

Abstract

A converter for generating photons from an electron beam is provided. The converter may include a plurality of converter plates (i) positioned perpendicular to an axis and (ii) arranged consecutively in a direction along the axis from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates. The first converter plate may be configured to receive the electron beam traveling in a direction along the axis. Furthermore, the first converter plate may have a thickness smaller than a thickness of the last converter plate, the thickness of the particular converter plate being measured along the axis.

Description

[Technical field]

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with Government support under Contract No. DE-AC02-06CH11357 awarded by the U.S. Department of Energy to UChicago Argonne, LLC, which operates Argonne National Laboratory. The Government has certain rights in this invention.

[0002] The present disclosure relates to methods and systems for producing radioisotopes, and in particular to a converter apparatus for converting an electron beam into electromagnetic radiation. [Background technology]

[0003] Radioisotopes are used in a variety of applications, including nuclear medicine, biomedical research, and aerospace technology. To produce such radioisotopes, an electron beam generated by an electron accelerator can be directed at a converter constructed of a material with a high atomic number (Z). Interaction of the high-energy electrons of the electron beam with the atomic nuclei of the converter material produces high-energy photons in a phenomenon called bremsstrahlung. The photons produced by the converter then irradiate a target material placed downstream of the converter, where a photonuclear reaction in the target material produces the radioisotope.

[0004] The photon-generating interactions between the electrons and the converter also deposit a significant amount of heat in the converter. As a result, the converter must be cooled (e.g., by passing water or gas over the surface of the converter). However, the heat that deposits on the converter may exceed the ability of the cooling mechanisms to effectively cool the converter. Excessive heating may degrade the converter and / or may cause the coolant to boil, further reducing the effectiveness of the coolant. Thus, there is a need for improved converters that can be effectively cooled without reducing the yield of the radioisotope. Summary of the Invention

[0005] In an exemplary embodiment, a converter for generating photons from an electron beam is provided. The converter may include a plurality of converter plates (i) positioned perpendicular to an axis and (ii) arranged consecutively in a direction along the axis from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates. The first converter plate may be configured to receive the electron beam traveling in a direction along the axis. Furthermore, the first converter plate may have a thickness less than a thickness of the last converter plate, the thickness of the particular converter plate being measured along the axis.

[0006] In another exemplary embodiment, a system for producing a radioisotope is provided. The system may include a converter for generating photons from an electron beam. The converter may include a plurality of converter plates (i) positioned perpendicular to an axis and (ii) arranged consecutively in an axial direction from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates. The first converter plate may be configured to receive the electron beam traveling in the axial direction. Furthermore, the first converter plate may have a thickness smaller than a thickness of the last converter plate, and the thickness of the particular converter plate is measured along the axis. The system may also include a target housing, positioned downstream of the converter in an axial direction such that photons generated by the converter using the electron beam illuminate the target housing.

[0007] In a further exemplary embodiment, a method for producing a radioisotope is provided. The method may include directing an electron beam along an axis toward a converter, the converter configured to convert the electron beam into photons. The converter may include a plurality of converter plates (i) positioned perpendicular to the axis and (ii) arranged consecutively in an axial direction from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates. The first converter plate may be configured to receive the electron beam traveling in an axial direction. Furthermore, the first converter plate may have a thickness less than a thickness of the last converter plate, the thickness of the particular converter plate being measured along the axis. The method may also include positioning a target housing supporting a target downstream of the converter in an axial direction such that the target is illuminated by photons generated by the converter. [Brief description of the drawings]

[0008] The figures described below illustrate various aspects of the systems and methods disclosed therein. It should be understood that each figure illustrates an example of a particular aspect of the disclosed systems and methods, and each of the figures is intended to correspond to a possible example thereof. Furthermore, wherever possible, the following description will refer to reference numerals contained in the following figures, where features illustrated in multiple figures will be designated with consistent reference numerals.

[0009] Although the drawings show arrangements that are currently considered, it being understood that examples of the invention are not limited to the precise arrangements and instrumentalities shown.

[0010] [Figure 1] 1 illustrates a cross-sectional view of an exemplary system for producing radioisotopes, according to some embodiments. [Diagram 2] 2 is a cross-sectional view of an exemplary converter that may be included in the system of FIG. 1. [Figure 3A]3 is an exemplary graph illustrating heat flux at various distances from an electron beam source for a typical converter and a converter constructed in accordance with the techniques of this disclosure, such as the converter of FIG. 2. [Figure 3B] 1 is an exemplary graph showing converter plate temperature as a function of beam power. [Figure 4] FIG. 2 is a cross-sectional view of an exemplary modular system for producing radioisotopes, which may be the system shown in FIG. [Diagram 5] FIG. 1 is a flow diagram of an exemplary method for producing a radioisotope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present disclosure is directed to converter designs that improve both the heat distribution within the converter and the overall radioisotope yield. Converters are typically divided into a series of aligned parallel converter plates to increase the converter surface area through which coolant can flow. However, in conventional converters, these converter plates have equal thickness. The converter designs of the present disclosure include converter plates of different thicknesses. In particular, the thickness of the converter plates is optimized such that the peak heat density deposited on each plate due to the incident electron beam is approximately equal. Such optimization distributes heat more evenly throughout the converter, reducing both the maximum and average temperatures of the converter as compared to converter plates of equal thickness. Furthermore, the converter designs may allow fewer electrons to reach the target (downstream of the converter) depending on the total thickness of the converter plates, thus reducing heat at the target and improving target survival. The converter designs of the present disclosure are primarily referenced with reference to Figures 2-3B. Figures 1 and 4 are included to illustrate systems in which the converters of the present disclosure may operate.

[0012] Referring to the figures, FIG. 1 is a cross-sectional view of an exemplary system 100 for producing radioisotopes. It should be appreciated that the system 100 is merely an example and alternative or additional components are contemplated. The system 100, which may also be referred to as a radioisotope target station, includes a converter 104 and a target capsule 108 having a cavity 106. The cavity 106 is adapted to receive a target such that the target capsule 108 encapsulates the target. The target is a material that can produce a radioisotope when exposed to photons of appropriate energy. Thus, the system 100 is positioned such that the electron beam 102 strikes the converter 104, and photons generated by the interaction of electrons in the electron beam 102 with the converter 104 irradiate the target to produce a radioisotope. Exemplary radioisotopes that may be produced include Cu-67, Ac-225, Sc-47, Re-186, Re-188, Re-189, As-76, As-77, Lu-177, Rh-105, Au-196, Pt-195m, and combinations thereof. Thus, the techniques of the present disclosure can be used with a variety of different target materials to arrive at a desired target radioisotope.

[0013] The electron beam 102 may be generated by a particle accelerator, such as a linear accelerator (linac). The line along which the electron beam 102 travels may be referred to as the electron beam axis 103 in this disclosure. The system 100 may be positioned along the beamline of the particle accelerator such that the tunnel defined by the system 100 is coaxial with the electron beam axis 103. The electron beam 102 enters the system 100 at the upstream end 110 of the tunnel. The electron beam 102 then passes through a beam entrance window 118. The beam entrance window 118 may be, for example, 0.1 millimeters to 2 millimeters thick. Different materials, or window thicknesses or shapes, may be utilized to maximize heat transfer. Exemplary materials include aluminum, titanium, copper, beryllium, and steel. After passing through the beam entrance window 118, the electrons enter the converter 104.

[0014] The converter 104 includes a plurality of converter plates 120. The converter plates 120 may be supported by a converter carrier 116. For example, the converter carrier 116 may have a plurality of slots, each slot receiving a converter plate 120. As used herein, the converter 104 includes the converter plates 120 and the converter carrier 116. The system 100 includes a converter housing 114 that supports the converter carrier 116. As shown in FIG. 4, in some embodiments, the converter carrier 116 is removably received by the converter housing 114 such that the converter carrier 116 can be removed from the converter housing 114 (e.g., by sliding the converter carrier 116 out from under the converter housing 114). In other embodiments, the converter carrier 116 is permanently fixed within or is part of the converter housing 114.

[0015] The converter plates 120 are disposed perpendicular to the path of the electron beam 102 (i.e., perpendicular to the electron beam axis 103). Additionally, the converter plates 120 are disposed consecutively along the electron beam axis 103 and are parallel to one another. The converter plates 120 are aligned with one another along the electron beam axis 103 and may have the same height and width (i.e., dimensions measured in a plane perpendicular to the electron beam axis 103). The thickness and relative positioning of the converter plates 120 are discussed in more detail below with respect to FIG. 2, in which the thickness of the converter plates 120 is measured along the electron beam axis 103. Each of the converter plates 120 may be constructed of a material having a high atomic number (Z) (i.e., Z of 72 or greater). Exemplary materials for the converter plates 120 include tungsten (W), tantalum (Ta), gold (Au), lead (Pb), or a combination of high-Z materials. In various embodiments, some converter plates 120 may be constructed of a different material than other converter plates 120. In other embodiments, each converter plate 120 may be constructed of the same material. In some embodiments, one or more converter plates 120 may be constructed of an alloy or other non-elemental material.

[0016] As the electron beam 102 travels through the converter plate 120, the electrons interact with nuclei of the high-Z converter material to generate photons. When the electrons are decelerated by the converter plate 120, the deceleration of the electrons produces electromagnetic radiation called bremsstrahlung radiation. Depending on the implementation, the converter 104 may be a fully stopped converter or a non-fully stopped converter. A fully stopped converter stops all electrons in the converter (i.e., substantially all of the kinetic energy of the incident electrons is converted to photon energy). Conversely, a non-fully stopped converter allows electrons to pass through the converter. The converter 104 may be a fully stopped converter or a non-fully stopped converter depending on the particular application. Generally speaking, a fully stopped converter includes a larger total thickness of converter material (i.e., the total thickness of the multiple converter plates 120) than a non-fully stopped converter. The converter plates 120 may or may not be in contact with each other depending on the implementation. Generally speaking, however, at least some of the converter plates 120 are disposed relative to one another to allow coolant (provided to the converter housing 114 by coolant passages 126, described below) to flow between the converter plates 120.

[0017] The photons generated by the converter 104 travel toward a cavity 106 adapted to receive a target capsule 108, which may further support a target (not shown), the target including a material in which a photonuclear reaction occurs to produce a radioisotope. The target is thus illuminated by the generated photons, which induce a photonuclear reaction in the target that produces a radioisotope. The target may include a material amount ranging from milligrams to over 100 grams, depending on the implementation. Furthermore, the target material may be selected depending on the desired radioisotope. For example, the target material may be zinc (Zn)-68, which may produce copper (Cu)-67 radioisotope. Any remaining photons, electrons, or other particles exit the tunnel at a downstream end 112 or are scattered along the tunnel.

[0018] The target capsule 108 is supported by a target carrier 124, which may in turn be supported by a target housing 122. The target capsule 108 is received within the target carrier 124 such that the longitudinal axis of the target capsule 108 is coaxial with the electron beam axis 103. That is, the target housing 122 (and the components supported by the target housing 122, including the target carrier 124 and the target capsule 108) are configured such that the target (occupying space within the cavity 106) is held within a tunnel that is coaxial with the electron beam axis 103. The target capsule 108, target carrier 124, and target housing 122 are further discussed with reference to FIG. 4.

[0019] The coolant passage 126 provides coolant to the converter housing 114, and the coolant passage 128 provides coolant to the target housing 122. Although not shown for cross-sectional views, the system 100 may also include an outlet passage for each of the coolant passages 126, 128 to remove the coolant from the system 100. Thus, the coolant can flow through the coolant passage 126, through the converter 104, and exit via an outlet passage (not shown). Similarly, the coolant can flow through the coolant passage 128, through the target housing 122, and exit via an outlet passage (not shown). The coolant may pass through both the converter housing and the target housing, either sequentially or individually. After the coolant is received at the converter housing 114 from the coolant passage 126, the coolant may be routed through components of the converter 104 via fluid channels to cool the converter 104, and then flow out of the converter housing 114 via an outlet passage. In particular, the coolant may be directed through the gaps between adjacent converter plates 120. The coolant may be in direct contact with the converter plates 120. Similarly, after the coolant is received in the target housing 122, the coolant may be routed through components of the target housing 122 via fluid channels and then flow out of the target housing 122 via an exit passageway. For example, the target capsule 108 may be in direct contact with the coolant.

[0020] The coolant is typically a fluid such as water, ethylene glycol, diethylene glycol, propylene glycol, or combinations thereof. The coolant carried by the coolant passages 126 may be different from the coolant carried by the coolant passages 128, depending on the implementation. Generally, the coolant traverses the converter housing 114 and the target housing 122 at a rate and temperature to maintain the temperature of the housings 114, 122 below the boiling point of the coolant and / or below the melting point of the lowest melting point component of the housings 114, 122. For example, if water is used as the coolant, the temperature is maintained such that the water is kept below 100°C. If the converter housing 114 or the target housing 122 is constructed of aluminum, the temperature of the converter housing 114 or the target housing 122 is maintained below approximately 600°C, given that aluminum melts at 660°C. The rate, temperature, and type of coolant for each of the converter housing 114 and the target housing 122 may vary depending on the desired temperature of each respective housing 114, 122. Alternatively or in addition, portions of the system 100 may be adapted to receive a pressurized gas, such as pressurized helium, as a coolant. For example, in some implementations, the converter plate 120 may be cooled by gas moving at high velocity across the converter plate 120.

[0021] Referring now to Figure 2, the converter design of the present disclosure will be discussed. Figure 2 is a cross-sectional view of an example converter 200 that may be included in the system 100 of Figure 1. As such, Figure 2 may represent an expanded view of the converter 104 of Figure 1. Nevertheless, although the converter 200 is described with reference to the system 100, it should be understood that the converter 200 may be included in any system that includes a converter for converting a particle beam into photons.

[0022] FIG. 2 also includes index 201 indicating exemplary materials that may comprise the components of converter 200 shown in FIG. 2. For sections shown as containing water (e.g., passages 230, 232, 234), the sections may be passages defined by the components of system 100 through which a coolant such as water may flow. Similarly, for sections shown as containing helium and nitrogen, the sections may be passages through which a pressurized gas such as helium or nitrogen may be present. As indicated by index 201, converter carrier 116, converter housing 114, and target carrier 124 may be constructed and / or shielded using aluminum (Al). Beam entrance window 118 may also be shielded with Al. Target capsule 108 may be constructed of ceramic. In other embodiments, target capsule 108 may be constructed of another material suitable for separating the target from the coolant or simply containing the target.

[0023] Figure 2 further includes a horizontal axis indicating the thickness of the exemplary component in centimeters, where the thickness is measured along the electron beam axis 103. The horizontal axis of Figure 2 is therefore parallel to the electron beam axis 103. Figure 2 also includes a vertical axis indicating the height of the exemplary component in centimeters. On the vertical axis, the center of the electron beam 102 is located at a height of approximately 0 cm.

[0024] 2 illustrates both converter 200 and other components of system 100, which are shown so that converter 200 can be viewed in the context of system 100. Converter 200 includes converter plate 120 and converter carrier 116, which supports converter plate 120. A coolant, which corresponds to water in FIG. 2, may flow between beam entrance window 118 and converter 200 in passage 230, between converter plate 120 in passage 232, and in a forward flow channel 234 defined by target carrier 124 and target capsule 108.

[0025] In the example illustrated in FIG. 2, there are 18 converter plates labeled 120A through 120R, with the first converter plate (the converter plate most upstream and closest to the beam entrance window 118) labeled with reference number 120A, the second converter plate labeled with reference number 120B, and so on. The penultimate converter plate is labeled with reference number 120Q, and the last converter plate (the converter plate most downstream and closest to the target capsule 108) is labeled with reference number 120R. The converter plates 120A through 120R are disposed perpendicular to the electron beam axis 103, with the electrons of the electron beam 102 traveling horizontally from left to right in FIG. 2. The converter plates 120 are separated by a distance of approximately 1 mm (i.e., 1 mm + / - 0.5 mm). In some embodiments, the spacing between at least some of the converter plates 120 may be different. In other embodiments, the spacing between the converter plates 120 is the same.

[0026] The electron beam 102 passes through the beam entrance window 118 and is received by the first converter plate 120A. The electron beam 102 continues to travel through the remaining converter plates 120B-120R. As the electron beam 102 passes through the converter plate 120, the electrons are stopped due to the kinetic energy of the electrons being converted into photons. The photons travel downstream and irradiate the target capsule 108 and further the target within the cavity 106 of the target capsule 108. In the example of FIG. 2, the target is comprised of zinc.

[0027] As briefly discussed above, conventionally, converter plates are of the same thickness. However, this results in a large amount of heat being deposited on the first few converter plates, as the electron beam 102 is narrowest on the first, i.e., most upstream, converter plate. This effect is illustrated by a simulation performed by the applicant, shown in FIG. 3A. In FIG. 3A, heat flux (watts per square centimeter) is plotted as a function of component number, where the heat flux represents the heat deposited on the component (i.e., converter plate) as a result of the electron beam. For the converter to operate effectively, this heat should be carried away from the converter plate by the coolant flowing between the plates. However, excessive heat can exceed the capacity of the coolant, leading to heat buildup within the converter, which can result in boiling of the coolant, destruction of the converter plate, and / or destruction of the converter housing.

[0028] 3A, the component numbers increase in the downstream direction. Thus, beam entrance window 118 corresponds to component zero, the first slot in which a converter plate can be placed (i.e., the first slot in converter carrier 116) corresponds to component 1, etc. The 18th slot in which a converter plate can be placed corresponds to component 18, the entrance to target carrier 124 corresponds to component 19, and target capsule 108 corresponds to component 20.

[0029] Run 1 in FIG. 3A corresponds to simulated data for a typical converter plate, i.e., converter plates having the same thickness. In run 1, aluminum plates were placed in slots 1-6. The aluminum, with its low Z, allows most electrons to pass without much interaction, and therefore minimal heat is deposited. The aluminum was placed to maintain equal flow of coolant between all plates. Thus, the most upstream converter plate is located in slot 7. As can be seen in FIG. 3A, this most upstream converter plate has a large heat flux (greater than 100 W / cm2). The heat flux increases with each successive converter plate, reaching a peak at the converter plate placed in slot 10. The heat flux then drops off for the remaining converter plates.

[0030] However, returning to Figure 2, in contrast to conventional converter plates, at least a portion of the converter plates 120 have different thicknesses. Furthermore, the thicknesses of the converter plates 120 are optimized so that the same energy density is deposited on each converter plate 120. Thus, for each converter plate 120, the coolant flowing in the gaps between adjacent converter plates 120 removes the same amount of heat.

[0031] Generally, the optimized converter design of the present disclosure includes a first converter plate having a smaller thickness than the last converter plate. Thus, the first converter plate 120A has a smaller thickness than the converter plate 120R. However, the converter plates 120B-120Q do not necessarily have a constant increasing thickness. The highest amount of energy is not necessarily deposited on the first converter plate 120A due to an effect known as electron shower. When electrons hit the first converter plate 120A, the impinging electrons may generate additional electrons or particles that travel downstream and hit the second converter plate 120B. To counteract this effect, the second converter plate 120B may have a smaller thickness than the first converter plate 120A. Similarly, the third converter plate 120C may have a smaller thickness than the second converter plate 120B. The thicknesses of the third converter plate 120C-sixth converter plate 120F may have the same thickness. The thickness of the seventh converter plate 120G may be the same as the thickness of the second converter plate 120B (and thus greater than the thickness of the sixth converter plate 120F). The thickness of the eighth converter plate 120H may be the same as the thickness of the first converter plate 120A. The thickness of the ninth converter plate 120I may be greater than the thickness of the eighth converter plate 120H. The thicknesses of the tenth converter plate 120J through the eighteenth converter plate 120R may be in ascending order of size (i.e., thickness of the eighteenth converter plate 120R>thickness of the seventeenth converter plate 120Q>thickness of the sixteenth converter plate 120P>...>thickness of the eleventh converter plate 120K>thickness of the tenth converter plate 120J).

[0032] Returning to FIG. 3A, run 2 corresponds to simulated data for an optimized plate, i.e., converter plate 120. In contrast to run 1, there is a converter plate in each of the 18 slots. Thus, the first converter plate 120A is component number 1. Although there are fewer converter plates in run 1 than in run 2 (because run 1 uses fewer slots than run 2), the total converter thickness is substantially the same in run 1 and run 2. In contrast to run 1, the heat flux per square centimeter is substantially constant over the majority of the converter plate. Due to the drop in electron energy as the electrons pass through the converter plate 120, the heat flux density decreases after the 16th converter plate 120P. Advantageously, in addition to the heat flux density remaining constant, the maximum heat flux density of the optimized plate is also lower than the conventional plate. In addition, FIG. 3A also shows that fewer electrons are able to pass through the converter plate 120 compared to the conventional plate. As a result, the heat flux density at the target capsule 108 (component number 20) of the converter plate 120 is lower than the conventional plate. Heating of the target can cause decomposition or melting of the target, resulting in a lower yield of radioisotopes produced. Compared to conventional plates, the optimized plates have a lower maximum heat flux density, a lower average heat flux density, and a more evenly distributed heat flux density, and therefore can be cooled more efficiently. Furthermore, the optimized plates improve the yield of radioisotopes by allowing a higher electron flux to bombard the converter without damaging it.

[0033] Further, referring to FIG. 3B, the optimized design of the converter plate 120 also increases the maximum beam power available compared to the conventional plate. FIG. 3B shows experimental data collected by the applicant using thermocouples placed on the converter plate 120. The horizontal axis is beam power (kW) and the vertical axis is temperature (° C.). The plot corresponds to the maximum surface temperature of one of the converter plates 120. The saturation temperature marked as 124° C. corresponds to the upper limit for the desired temperature. This upper limit is selected for a particular coolant, in this case water. Furthermore, the upper limit is selected based on an estimate of the amount of heat that can be removed by the coolant, which depends on the energy deposited on the converter plate 120 and the flow rate of the coolant. Below this upper limit, incipient boiling of the coolant moving through the converter plate 120 is avoided. Above this upper limit, the coolant may boil. A different upper limit can be selected based on the heat resistance of the coolant and the particular application.

[0034] FIG. 3B shows three data sets corresponding to the surface temperature of the converter plate 120 as a function of beam power for electron beams with three different beam widths (measured as full width at half maximum (FWHM)): 10 mm, 8 mm, and 5 mm. The temperature of the converter plate 120 can be measured by placing a thermocouple on the converter plate 120. As shown in FIG. 3B, the use of the optimized converter plate 120 allows the use of beam powers up to at least 20 kW for beam widths of 8 mm and 10 mm. Even at 20 kW, the surface temperature of the converter plate remains below the saturation temperature for beam widths of 8 mm and 10 mm. For beam widths of 6 mm, the surface temperature of the converter plate remains below the saturation temperature up to beam powers of approximately 13.5 kW. Due to the optimized nature of the converter plate 120, higher beam powers can be used than with conventional plates, which results in higher radioisotope yields.

[0035] Table 1 provides exemplary thickness measurements for the converter plate 120. The thickness may vary depending on the characteristics of the electron beam 102. In particular, to have a full stop converter, different amounts of total converter thickness (i.e., the sum of the thicknesses of the individual converter plates) are required for different beam energies. That is, for larger beam energies, a larger total converter thickness is required than for smaller beam energies. An exemplary total converter thickness may be 1 mm to 10 mm, depending on the beam energy, and an exemplary individual converter plate thickness may be 0.1 mm to 2 mm, depending on the total number of plates. Exemplary converter plate thickness measurements for a 40 MeV electron beam and a 35 MeV electron beam are shown in Table 1 below. [Table 1]

[0036] Table 1: Exemplary thicknesses of converter plates The exemplary thicknesses shown in the first column of Table 1 are optimized for 18 converter plates constructed of tantalum (Ta), an electron beam having an energy of 40 MeV, and a target material of Zn-68, for the purpose of producing Cu-67 radioisotope. The exemplary thicknesses shown in the second column are optimized for the same set of experimental parameters, except that the electron beam has an energy of 35 MeV. The thickness of the 35 MeV electron beam can be derived by multiplying the thickness of the 40 MeV electron beam by 7 / 8 (i.e., the ratio of the beam energies, 35 MeV / 40 MeV). Thus, based on the exemplary measurements given in Table 1, other exemplary measurements can be derived for other beam energies.

[0037] The thickness of the converter plates 120 can be optimized for any experimental setup and can vary depending on the implementation (e.g., parameters such as the intensity and size of the electron beam, the target material, the desired radioisotope, the converter material, the cooling material / method, etc.). As an example, if more than 18 slots are available in the converter carrier 116 (or other suitable device to receive the converter plates), then there can be more than 18 plates. Conversely, if less than 18 slots are available in the converter carrier 116 (or other suitable device to receive the converter plates), then there can be less than 18 plates. Thus, the thickness of the converter plates 120 can be adjusted for more or fewer plates 120, while the total converter thickness remains constant (e.g., thick enough to function as a full stop converter, depending on the application). In these examples, the first converter plate 120 is still thinner than the last converter plate 120. The second converter plate 120 can have a thickness less than the first converter plate 120. If there are more than 18 plates, the third converter plate 120 may have a thickness less than the second converter plate 120, and the fourth converter plate 120 may have a thickness less than the third converter plate 120. One or more converter plates 120 (e.g., starting with the fourth converter plate 120) may have the same thickness. If there are more than 18 plates, the third converter plate 120 may have a thickness less than the second converter plate 120 or may have the same thickness as the second converter plate 120. One or more converter plates 120 (e.g., starting with the second or third converter plate 120) may have the same thickness. In any example (i.e., more or less than 18), two or more of the last converter plates 120 may have thicknesses in ascending order, with the last converter plate 120 having the greatest thickness.

[0038] As another example, while the above discussion has focused primarily on dead-end converters, the converter designs of this disclosure can also be adapted to provide non-dead-end converters. For example, the downstream plate can be removed or replaced with a low-Z material (i.e., aluminum) until the desired number of electrons can pass through the converter.

[0039] Generally speaking, according to the converter design of the present disclosure, the converter plates are optimized so that the energy density (or heat flux per square centimeter) deposited on each converter plate is the same. This optimization results in a first converter plate having a thickness smaller than the last converter plate. The second converter plate may have a thickness smaller than the thickness of the first converter plate. One or more plates downstream of the second converter plate (e.g., the third converter plate to the sixth converter plate) may have a thickness that may be smaller than or the same as the thickness of the second plate. After the sixth converter plate, the thickness of the converter plates may increase such that the last converter plate has the maximum converter plate thickness.

[0040] FIG. 4 is a cross-sectional view of an exemplary system 400 for producing radioisotopes. The system 400 may be the system 100 shown in FIG. 1, but FIG. 4 is provided in addition to FIG. 1 to provide a more detailed view of the system 100. The system 400 is one exemplary radioisotope target station that may utilize the converter design of the present disclosure (i.e., the converter design described with reference to FIG. 2). However, it should be understood that the converter design of the present disclosure may be utilized in any suitable system, i.e., any suitable system having a converter configured to convert an incident particle beam into electromagnetic radiation. For example, the exemplary system 400 is a modular system having a target carrier and a converter carrier in slidable communication with their respective housings, but the converter design of the present disclosure may also be readily utilized in non-modular systems. As previously discussed, the system 400 may be positioned along a beamline of a particle accelerator such that a tunnel 402 defined by the system 400 is coaxial with the electron beam axis 103. The electron beam 102 enters the system 400 at the upstream end 110 of the tunnel 402, passes through a beam entrance window 118, and is received by the converter plate 120, which converts the electron beam 102 into photons that illuminate a target within the target capsule 108. Any remaining photons, electrons, or other particles either exit the tunnel 402 at the downstream end 112 or are scattered along the tunnel 402.

[0041] 4, the target carrier 124 and the converter carrier 116 are configured to be removably received by the target housing 122 and the converter housing 114, respectively. The modular design allows the system 400 to be adapted to changing launch and beamline configurations. For different applications, the target carrier 124 and / or the converter carrier 116 can be removed from the target housing 122 and / or the converter housing 114, respectively, and configured according to the desired experimental objectives.

[0042] The target carrier 124 can be removed from the target housing 122, for example, to retrieve the target capsule 108. The target housing 122 and the converter housing 114 are shielded, except for a beam entrance window 118 that includes a narrow gap that allows the electron beam to enter the converter housing 114. The shielding minimizes any potential radiation dose to personnel during retrieval of the target capsule 108 (and the target supported therein). Additionally, in some embodiments, the target carrier 124 can be retrieved by remote actuation of a mechanical arm that lifts the target carrier 124 out of the target housing 122 into a shielded transfer cask. In such embodiments, personnel are not exposed to a direct irradiation environment caused by the target or the converter 104.

[0043] The target carrier 124 may be in slidable communication with the target housing 122 such that the target carrier 124 can slide in and out of the target housing 122 via a top portion of the target housing 122. The top-loading configuration allows for "hot swapping" an irradiated target for a new target, which can then be placed into a standard hot cell. The target carrier 124 is adapted to receive the target capsule 108.

[0044] The target carrier 124 may be hermetically sealed with the target housing 122. For example, in some embodiments, the target carrier 124 may include an annular groove 430, which may be adapted to receive an O-ring 432. The O-ring 432 may be adapted to frictionally engage an inwardly facing surface of the target housing 122. In other embodiments, the target carrier 124 may seal with the target housing 122 via a male / female thread and groove arrangement.

[0045] The upper end 429 of the target carrier 124 may define an upwardly projecting tongue 431 with an area forming an opening 434. The opening 434 may serve as a gripping point for a crane or other means for removing the target carrier 124 from the target housing 122 or for inserting the target carrier 124 into the target housing 122.

[0046] The target carrier 124 is generally configured to stabilize the target capsule 108 (and the target material within the target capsule 108) relative to the electron beam axis 103 as coolant flows across the target capsule 108. The target capsule 108 may be removably secured within the target carrier 124 via fastening means to prevent rattling of the target capsule 108 within the target carrier 124 during cooling operations. A suitable fastening means is a male-female threaded arrangement, whereby, for example, a circumferential surface of the target capsule 108 is threadably received by an inwardly facing surface of the target carrier 124.

[0047] 1 and 4 as separate components, in some implementations the converter housing 114 and the target housing 122 may be integrally molded as a unitary part. The target carrier 124 and the converter carrier 116 may then be removably received by such parts.

[0048] The coolant received from the coolant passage 126 may flow through channels in the converter housing 114. For example, the coolant may flow between the beam entrance window 118 and a first one of the converter plates 120, between the converter plates 120, and / or between the last converter plate and the converter carrier 116 or the converter housing 114. The forward flow channel 234 and the target housing channel 428 may be formed in the target housing 122 and may carry the coolant provided by the coolant passage 128. Other passages (not labeled), which may not be shown by FIG. 4, may be present in the housings 114, 122 to carry the coolant through the system 400.

[0049] The converter plate 120 may be positioned on a pedestal formed by the converter carrier 116. During operation of the electron beam, the converter carrier 116 may be sealed to the converter housing 114 by one or more O-rings 436 (e.g., metal O-rings such as aluminum (Al) or gold (Au) O-rings). The O-rings 436 may be received by annular grooves formed in the converter carrier 116. Lateral openings 442 may be formed in areas of the converter carrier 116 and align with dependent surfaces of the converter housing 114. The lateral openings 442 may be adapted to receive fasteners 440, such as screws, that fasten the converter carrier 116 to the converter housing 114.

[0050] The converter carrier 116 may be removably received by the converter housing 114. Thus, the converter carrier 116 may be removed from the converter housing 114 and the converter plates 120 held by the converter carrier 116 may be replaced, removed, exchanged, or moved. As previously mentioned, the converter carrier 116 may have slots that receive the converter plates 120. Some of the slots may not be occupied by the converter plates 120, depending on the implementation. Furthermore, the converter carrier 116 itself may be removed from the converter housing 114 and replaced with a different converter carrier having different converter plates. The converter carrier 116 may be in thermal communication with the converter housing 114 to take advantage of the coolant flowing through the converter housing 114. Alternatively or in addition, the converter carrier 116 may define a passage for the coolant.

[0051] 5 is a flow diagram of an exemplary method 500 for producing a radioisotope. In block 502, the method 500 includes directing an electron beam (e.g., electron beam 102) along an axis (e.g., electron beam axis 103) toward a converter (e.g., converter 104) configured to convert the electron beam into photons. The converter includes a plurality of converter plates (e.g., converter plate 120) that are (i) positioned perpendicular to the axis and (ii) consecutively arranged in the axial direction from a first converter plate (e.g., converter plate 120A) of the plurality of converter plates to a last converter plate (e.g., converter plate 120R) of the plurality of converter plates. The first converter plate is configured to receive the electron beam traveling in the axial direction. Furthermore, the first converter plate (e.g., converter plate 120A) has a thickness that is smaller than a thickness of the last converter plate (e.g., converter plate 120R), the thickness of the particular converter plate being measured along the axis.

[0052] In some implementations, at least three of the plurality of converter plates are positioned in ascending order of thickness in the axial direction (e.g., converter plates 120P-R in the example measurements in Table 1). Each of the at least three of the plurality of converter plates may have a different thickness. In some implementations, the thickness of the last converter plate is the maximum thickness of the plurality of converter plates.

[0053] In various implementations, a second converter plate positioned after (i.e., downstream of) the first converter plate and before the last converter plate in the axial direction (e.g., converter plate 120B or converter plate 120A) has a thickness less than the thickness of the first converter plate. In such implementations, at least two of the multiple converter plates (i) are positioned after the first converter plate along the axis and (ii) may be positioned in ascending order of thickness in the axial direction.

[0054] The converter may further include a converter carrier (e.g., converter carrier 116) adapted to support a plurality of converter plates. The converter carrier may be removably received by the converter housing (e.g., converter housing 114). For example, the converter carrier may be in slidable communication with the converter housing.

[0055] Depending on the implementation, adjacent converter plates of the plurality of converter plates may be spaced apart along the axis by 0.5 mm to 1.5 mm (e.g., adjacent converter plates may be spaced apart by approximately 1 mm). The converter may be adapted to receive a coolant fluid, such as water, between adjacent converter plates of the plurality of converter plates. Each of the plurality of converter plates may have a thickness of 0.1 mm to 2 mm depending on the implementation and how far upstream or downstream the converter plate is located relative to other converter plates of the plurality of converter plates. A total thickness, which is equal to the sum of the thicknesses of the plurality of converter plates, may be approximately 1 to 10 mm. Additionally, each of the plurality of converter plates may include a material within an atomic number of 72 or greater, such as W, Ta, Au, Pb, or a combination of these elements.

[0056] At block 504, the method includes positioning a target housing (e.g., target housing 122) supporting a target (e.g., a target material encapsulated by target capsule 108) downstream of the converter in an axial direction such that the target is illuminated by photons generated by the converter. The target produces a radioisotope in response to illumination by the photons. In some implementations, the target housing includes a target carrier (e.g., target carrier 124) supporting the target. The target carrier may be removably received by the target housing. The target carrier may be in slidable communication with the target housing, for example.

[0057] Aspects The following list of aspects reflects various embodiments expressly contemplated by the present application. Those of ordinary skill in the art will readily recognize that the following aspects are not intended to be limiting of the embodiments disclosed herein or to be exhaustive of all embodiments contemplated in light of the above disclosure, but instead are meant to be exemplary in nature.

[0058] Aspect 1. A converter for generating photons from an electron beam, comprising a plurality of converter plates: (i) positioned perpendicular to an axis; and (ii) arranged consecutively in a direction along the axis from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates, the first converter plate being configured to receive an electron beam traveling in a direction along the axis, the first converter plate having a thickness smaller than a thickness of the last converter plate, the thickness of a particular converter plate being measured along the axis.

[0059] Embodiment 2. A converter as described in embodiment 1, wherein at least three of the plurality of converter plates are positioned in order of ascending thickness in the axial direction.

[0060] Embodiment 3. A converter as described in embodiment 2, wherein at least three of the plurality of converter plates each have a different thickness.

[0061] Embodiment 4. The converter of embodiment 1, wherein the thickness of the last converter plate is the maximum thickness of the plurality of converter plates.

[0062] Embodiment 5. A converter as described in embodiment 1, wherein a thickness of a second converter plate positioned after the first converter plate and before the last converter plate in the axial direction is smaller than the thickness of the first converter plate.

[0063] Embodiment 6. A converter as described in embodiment 5, wherein at least two of the plurality of converter plates are (i) positioned behind the second converter plate along the axis and (ii) positioned in order of ascending thickness in the direction along the axis.

[0064] Embodiment 7. The converter of embodiment 1, further comprising a converter carrier adapted to support a plurality of converter plates, the converter carrier adapted to be in slidable communication with the converter housing.

[0065] A converter as described in embodiment 1, wherein adjacent converter plates of the plurality of converter plates are spaced apart along the axis by 0.5 millimeters to 1.5 millimeters.

[0066] A converter as described in embodiment 1, wherein each of the plurality of converter plates has a thickness of 0.1 millimeters to 2 millimeters.

[0067] A converter as described in embodiment 1, wherein the total thickness, equal to the sum of the thicknesses of the converter plates, is between 1 millimeter and 10 millimeters.

[0068] A converter according to an embodiment, wherein the converter is adapted to receive a coolant fluid between adjacent converter plates of the plurality of converter plates.

[0069] Example 12. A converter as described in example 1, wherein each of the plurality of converter plates comprises a material having an atomic number of 72 or greater.

[0070] Aspect 13. A system for producing a radioisotope, comprising: a converter for generating photons from an electron beam, the converter comprising: a plurality of converter plates, the plurality of converter plates (i) positioned perpendicular to an axis, and (ii) arranged consecutively in an axial direction from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates, the first converter plate being configured to receive an electron beam traveling in an axial direction, the first converter plate having a thickness smaller than a thickness of a last converter plate, the thickness of a particular converter plate being measured along the axis; and a target housing, the target housing positioned downstream of the converter in the axial direction such that photons generated by the converter using the electron beam irradiate the target housing.

[0071] Embodiment 14. The system of embodiment 13, wherein the target housing supports a target that produces a radioisotope in response to irradiation by photons.

[0072] Aspect 15. The system of aspect 13, wherein the target housing comprises a target carrier supporting a target that produces a radioisotope in response to irradiation by photons, the target carrier being removably received by the target housing.

[0073] Example 16. The system of Example 13, wherein the converter further comprises a converter carrier adapted to support a plurality of converter plates.

[0074] Aspect 17. The system of aspect 16, further comprising a carrier housing, the converter carrier being removably received by the carrier housing.

[0075] Embodiment 18. The system of embodiment 13, wherein at least three of the plurality of converter plates are positioned in ascending order of thickness in the axial direction.

[0076] Embodiment 19. The system of embodiment 18, wherein at least three of the plurality of converter plates each have a different thickness.

[0077] Aspect 20. A method for producing a radioisotope comprising: directing an electron beam along an axis toward a converter, the converter configured to convert the electron beam into photons, the converter comprising a plurality of converter plates, the plurality of converter plates (i) positioned perpendicular to the axis and (ii) arranged consecutively in an axial direction from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates, the first converter plate configured to receive the electron beam traveling in the axial direction, the first converter plate having a thickness less than a thickness of the last converter plate, the thickness of a particular converter plate being measured along the axis; and positioning a target housing supporting a target downstream of the converter in the axial direction such that the target is illuminated by photons generated by the converter.

[0078] Additional Considerations The following additional considerations apply to the above discussion: Throughout this specification, multiple instances may implement a function, component, operation, or structure that is described as a single instance. Although individual functions and instructions of one or more methods are illustrated and described as separate operations, one or more of the individual operations may be performed simultaneously, and the operations need not be performed in the order shown. Structures and functions presented as separate components in an exemplary configuration may be implemented as a combined structure or component. Similarly, structures and functions presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements are within the scope of the subject matter of this specification.

[0079] As used herein, any reference to "some embodiments," or "one embodiment," or "embodiments" means that a particular element, feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0080] Some embodiments may be described using the terms "coupled" and "connected," along with their derivatives. For example, some embodiments may be described using the term "coupled" to indicate that two or more elements are in direct physical or electrical contact with each other. However, the term "coupled" may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. The embodiments are not limited in this context.

[0081] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a function, process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements and may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, unless expressly stated to the contrary, "or" refers to an inclusive or, not an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist).

[0082] In addition, the use of "a" or "an" is used to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the description. This description should be read to include one or at least one, and the singular also includes the plural, unless otherwise clearly meant.

[0083] Furthermore, the figures depict, for purposes of example only, a preferred embodiment of system 100. Those skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be used without departing from the principles described herein.

[0084] Upon reading this disclosure, those skilled in the art will recognize still further alternative structural and functional designs for the methods and systems for producing radioisotopes through the principles disclosed herein. Thus, while specific embodiments and applications have been illustrated and described, it should be understood that the disclosed embodiments are not limited to the precise configuration and components disclosed herein. Various modifications, changes and variations that will be apparent to those skilled in the art may be made in the arrangement, operation and details of the methods and apparatus disclosed herein without departing from the spirit and scope as defined by the appended claims.

Claims

1. 1. A converter for generating photons from an electron beam, comprising: a plurality of converter plates (i) positioned perpendicular to an axis and (ii) arranged consecutively in a direction along the axis from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates; the first converter plate is configured to receive an electron beam traveling in the direction along the axis; A converter wherein the first converter plate has a thickness less than the thickness of the last converter plate, the thickness of a particular converter plate being measured along the axis.

2. A converter as described in claim 1, wherein one or more of the plurality of converter plates are composed of a first material and one or more of the plurality of converter plates are composed of a second material different from the first material.

3. A converter as described in claim 1 or 2, wherein each of the plurality of converter plates comprises a material having an atomic number of 72 or greater.

4. 3. The converter of claim 1, wherein at least three of the plurality of converter plates are positioned in order of increasing thickness in the direction along the axis, and wherein the spacing between the plurality of converter plates is variable.

5. The converter of claim 4 wherein each of the at least three of the plurality of converter plates has a different thickness.

6. 3. The converter of claim 1, wherein the thickness of the last converter plate is the maximum thickness of the plurality of converter plates.

7. 3. A converter as described in claim 1 or 2, wherein a thickness of a second converter plate positioned after the first converter plate and before the last converter plate in the direction along the axis is smaller than the thickness of the first converter plate.

8. 8. The converter of claim 7, wherein at least two of the plurality of converter plates (i) are positioned after the second converter plate along the axis, and (ii) are positioned in order of increasing thickness in the direction along the axis.

9. The converter of claim 1 or 2, further comprising a converter carrier adapted to support the plurality of converter plates, the converter carrier adapted to be in slidable communication with a converter housing.

10. 3. A converter as claimed in claim 1 or 2, wherein adjacent ones of said plurality of converter plates are spaced apart along said axis by between 0.5 millimeters and 1.5 millimeters.

11. 3. The converter of claim 1, wherein each of the plurality of converter plates has a thickness of between 0.1 millimeters and 2 millimeters.

12. 3. The converter according to claim 1, wherein a total thickness equal to the sum of the thicknesses of the converter plates is between 1 millimeter and 10 millimeters.

13. The converter of claim 1 or 2, wherein the converter is adapted to receive a coolant fluid between adjacent ones of the plurality of converter plates.

14. 1. A system for producing a radioisotope, comprising:

1. A converter for generating photons from an electron beam, comprising: a plurality of converter plates (i) positioned perpendicular to an axis and (ii) arranged consecutively in a direction along the axis from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates; the first converter plate is configured to receive an electron beam traveling in the direction along the axis; a converter, wherein the first converter plate has a thickness less than the thickness of the last converter plate, the thickness of a particular converter plate being measured along the axis; a target housing positioned downstream of the converter in the direction along the axis such that photons generated by the converter using the electron beam illuminate the target housing.

15. The system described in claim 14, wherein one or more of the plurality of converter plates are constructed of a first material and one or more of the plurality of converter plates are constructed of a second material different from the first material.

16. A system as described in claim 14 or 15, wherein each of the plurality of converter plates comprises a material having an atomic number of 72 or greater.

17. 16. The system of claim 14 or 15, wherein the target housing supports a target that produces the radioisotope in response to irradiation by the photons.

18. the target housing comprises a target carrier supporting a target that produces the radioisotope in response to irradiation by the photons; 16. The system of claim 14 or 15, wherein the target carrier is removably received by the target housing.

19. 16. The system of claim 14 or 15, wherein the converter further comprises a converter carrier adapted to support the plurality of converter plates.

20. 20. The system of claim 19, further comprising a carrier housing, the converter carrier being removably received by the carrier housing.

21. 16. The system of claim 14 or 15, wherein at least three of the plurality of converter plates are positioned in order of increasing thickness in the direction along the axis.

22. 22. The system of claim 21, wherein each of the at least three of the plurality of converter plates has a different thickness.

23. 1. A method for producing a radioisotope, comprising: directing an electron beam along an axis towards a converter, the converter configured to convert the electron beam into photons, the converter comprising: a plurality of converter plates (i) positioned perpendicular to the axis; and (ii) arranged consecutively in a direction along the axis from a first converter plate of the plurality of converter plates to a last converter plate of the plurality of converter plates; the first converter plate is configured to receive the electron beam traveling in the direction along the axis; orienting the first converter plate to have a thickness less than a thickness of the last converter plate, the thickness of a particular converter plate being measured along the axis; and positioning a target housing supporting a target downstream of the converter in the direction along the axis such that the target is illuminated by the photons generated by the converter.

24. The method described in claim 23, wherein one or more of the plurality of converter plates are constructed of a first material and one or more of the plurality of converter plates are constructed of a second material different from the first material.

25. The method described in claim 23 or 24, wherein each of the plurality of converter plates comprises a material having an atomic number of 72 or greater.

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