Radioisotope production target and target assembly, and method for producing radioisotopes

Abstract

This invention provides an irradiation target for producing a radioactive isotope. The irradiation target includes an outer tube extending along a first axis and an inner tube extending along a second axis. The inner tube includes an outer surface surrounded by the inner surface of the outer tube and a primary irradiation target material. The inner surface of the outer tube and the outer surface of the inner tube define an intermediate cavity therebetween. The irradiation target further includes a secondary irradiation target material positioned within the intermediate cavity. This invention also provides an irradiation target assembly and a method for producing a radioactive isotope.

Description

[Previous Technology]

[0001] The radioisotopes of concern (such as those useful in medicine) can be synthesized via nuclear reactions in an irradiation target and / or its assembly. Materials used in the irradiation target may include an irradiated material that interacts with incident radiation (such as, for example, a neutron flux in a nuclear reactor) to produce a primary emission; and a precursor material that interacts with the secondary radiation to result in a desired radioisotope. However, conventional irradiation targets may require multiple irradiation cycles because their irradiated material is prone to depletion before one of the precursor materials is converted, thereby increasing the time for radioactive material disposal and / or from initial irradiation to the final use of the desired radioisotope. Therefore, current production methods for synthesizing radioisotopes can suffer from problems associated with low production efficiency and / or increased safety hazards. Therefore, there is a need to develop alternative irradiation target assemblies and their production methods to optimize the efficiency and safety of radioisotope production. [Summary of the Invention]

[0002] The following overview is provided to facilitate understanding of some of the innovative features specific to the forms disclosed herein and is not intended to be a complete description. A complete understanding of the various forms disclosed herein can be obtained by considering the entire specification, claims, and abstract as a whole.

[0003] Among various embodiments, an irradiation target for producing a radioactive isotope is disclosed. In some embodiments, the irradiation target includes an outer tube extending along a first axis and an inner tube extending along a second axis. In some embodiments, the outer tube includes a first end, a second end, and an inner surface between the first end and the second end. In some embodiments, the inner tube defines an inner cavity therein and includes an outer surface surrounded by the inner surface of the outer tube and a primary irradiation target material positioned within the inner cavity. In some embodiments, the primary irradiation target material is configured to produce an emission based on exposure to a neutron flux. In some embodiments, the inner surface of the outer tube and the outer surface of the inner tube define an intermediate cavity therebetween. In some embodiments, the irradiation target includes a secondary irradiation target material positioned within the intermediate cavity. In some cases, the secondary irradiation target material is configured to interact with the emission produced by the primary irradiation target material to produce the radioactive isotope.

[0004] Among various embodiments, an irradiation target assembly for producing a radioactive isotope is disclosed. In some embodiments, the irradiation target assembly includes an outer tube extending along a central axis and including a first end and a second end, an inner tube extending along the central axis, a first end cap for the first end and a second end cap for the second end, and a target material. In some embodiments, the inner tube defines an inner cavity therein, and a certain amount of radium-226 is accommodated within the inner cavity. In some embodiments, the inner tube is surrounded by the outer tube, wherein a volume enclosed between the inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity. In some embodiments, the first end cap and the second end cap are removably attached to the first end and the second end of the outer tube to maintain an axial and lateral positioning of the inner tube within the outer tube. In some embodiments, the target material includes radium-226 and is positioned within the intermediate cavity.

[0005] Among various embodiments, a method for producing a radioactive isotope is disclosed. In some embodiments, the method includes exposing an irradiation target assembly to a neutron flux. In some embodiments, the irradiation target assembly includes an outer tube extending along a central axis and an inner tube extending along the central axis. In some embodiments, the inner tube is surrounded by the outer tube. In some embodiments, the inner tube includes a primary irradiation target material for generating an emission based on exposure to the neutron flux. In some embodiments, a volume enclosed between an inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity. In some embodiments, the irradiation target assembly includes a secondary irradiation target material positioned within the intermediate cavity, wherein the secondary irradiation target material interacts with the emission generated by the primary irradiation target material to produce the radioactive isotope.

[0006] These and other objects, features, and characteristics of the present invention, as well as the function of the related elements, the combination of components, and the economics of manufacture of the methods of operation and structures, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form part of this specification, wherein like element symbols designate corresponding portions in various figures. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to define the scope of any of the forms disclosed herein.

Implementation Method

[0013] Certain exemplary embodiments of the present invention will now be described to provide a general understanding of the principles of composition, function, manufacture, and use of the compositions and methods disclosed herein. Examples or several examples of these embodiments are illustrated in the accompanying drawings. It will be understood by those skilled in the art that the compositions, articles, and methods specifically described herein and illustrated in the drawings are non-limiting exemplary embodiments, and the scope of the various embodiments of the invention is defined only by the claims. Features illustrated or described in a single exemplary embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

[0014] Throughout the specification, references to "various examples," "some examples," "one example," "an example," or similar expressions mean that a particular feature, structure, or characteristic described in the examples is included in one example. Therefore, the phrases "in various examples," "in some examples," "in one example," "in one example," or similar expressions appearing in appropriate places throughout the specification do not necessarily all refer to the same example. Furthermore, a particular feature, structure, or characteristic may be combined in one example or several examples in any suitable manner. Therefore, a particular feature, structure, or characteristic illustrated or described in conjunction with an example may be combined, in whole or in part, with features, structures, or characteristics of another example or other examples without limitation. Such modifications and variations are intended to be included within the scope of this specification.

[0015] In the following description, the same element symbols designate the same or corresponding parts in several views of the drawing. Also in the following description, it should be understood that terms such as "forward," "backward," "left," "right," "above," "below," "upward," "downward," and the like are convenience terms and should not be construed as restrictive terms.

[0016] Typically, in a conventional nuclear reactor (such as a PWR), the reactor core may contain a large number of fuel assemblies, each of which comprises a plurality of elongated fuel elements or fuel rods. For example, FIG1 illustrates a cross-sectional front view of a reactor vessel 1 according to at least one non-limiting embodiment of the present invention. The reactor vessel 1 includes an organized array of elongated fuel rods 2 and a plurality of flux sleeves 3. The fuel rods 2 may contain a plurality of fuel pellets, each comprising a fissile material (such as an enriched uranium-based material) capable of sustaining a nuclear fission chain reaction. The flux sleeves 3 are typically accessed through a plurality of narrow perforations 4 connected to a conduit to a separate target transfer system. Fission neutrons (such as transient neutrons) are produced as a byproduct of such nuclear fission reactions and are slowed down by interaction with neutron moderating agents present in the reactor core. Thus, the energy level of transient fission neutrons is reduced to a thermal neutron energy. These thermally splitting neutrons can also participate in nuclear reactions with an irradiated target material located within the reactor core (such as in a flux sleeve) to produce one or more new nuclei and / or subatomic particles and / or energies. For example, a neutron capture reaction between a thermal neutron and gyrium-157 produces gyrium-158 accompanied by gamma radiation with energies greater than 6 megaelectron volts (MeV). Figure 2 shows a graph of gamma flux as a function of time, illustrating the depletion of 100 milligrams (mg) of 90% gyrium oxide (Gd₂O₃) enriched in gyrium-157. As shown in Figure 2, after approximately 5 days, a significant portion of gyrium-157 is depleted.

[0017] In the context of producing useful radioactive isotopes, a neutron flux including thermal neutrons (such as thermally splitting neutrons) can be used to irradiate a material that can directly or indirectly produce a desired radioactive isotope. For example, radium-226 can enter an excited state after interacting with gamma radiation produced by a neutron trapping reaction between a thermal neutron and thorium-157, a subsequent decay of which produces actinium-225, a medically useful radioactive isotope. In other words, radium-226 is activated to produce one of the precursors of the desired actinium-225 final product. Additional details are described in International Patent Application No. PCT / US2022 / 079372, filed November 7, 2022, entitled “PRODUCING AC-225 USING GAMMA RADIATION,” the entire contents of which are hereby incorporated herein by reference.

[0018] Irradiation targets can incorporate materials based on both uranium-157 and radium-226. However, the inventors of this invention have determined that in conventional irradiation targets, the dose of gamma radiation delivered to radium-226 can be substantially less than the actual amount of gamma radiation produced from uranium-157. This results in a higher proportion of uranium-157 required for a given amount of radium-226, and / or a longer irradiation time attributable to the relatively short half-life of actinium-225 (approximately 6.7 days), which increases the proportion of actinium-225 that has begun to decay before being removed from the reactor core. Therefore, the production of radioisotopes (such as actinium-225) using conventional irradiation targets can suffer from problems associated with process inefficiencies, increased production waste, and / or reduced product efficacy, thereby increasing costs and / or limiting the available supply of radionuclide-based therapies. The present invention provides an irradiation target and assembly, and a method for producing radioactive isotopes, which can mitigate the problems associated with currently available irradiation targets.

[0019] Figures 3 and 4 illustrate at least one non-limiting embodiment of an irradiation target assembly 1000 for producing radioactive isotopes according to the present invention. Figure 3 provides a schematic diagram of the irradiation target assembly 1000 and Figure 4 provides a cross-sectional view thereof. The irradiation target assembly 1000 includes an outer tube 1100 extending along a first axis, an inner tube 1200 extending along a second axis, a primary irradiation target 1300, and a secondary irradiation target 1400. In various embodiments, the outer tube 1100 is configured to have a cylindrical geometry. In some embodiments, the dimensions of the irradiation target assembly 1000 are configured to be installed within a flux sleeve of a nuclear reactor. For example, an outer diameter of the outer tube 1100 may be substantially the same as or slightly smaller than an inner diameter of a flux sleeve. In some embodiments, the outer tube 1100 has an outer diameter of approximately 4.78 millimeters ("mm").

[0020] Referring now to FIG. 3, the outer tube 1100 includes a first end 1110 and a second end 1120, and an inner surface 1102 between the first end 1110 and the second end 1120. During an irradiation cycle, while the irradiated target assembly 1000 is exposed to radiation (such as an incident thermal neutron flux in an operating reactor), the first end 1110 and / or the second end 1120 may be closed to retain the inner tube 1200, the primary irradiated target material 1300, and the secondary irradiated target material 1400. In various embodiments, the first end 1110 is closed using a first end cap 1130 and the second end 1120 is closed using a second end cap 1140. Other configurations of the outer tube 1100 are also contemplated in the present invention. For example, in some embodiments, one end of the outer tube 1100 may be permanently closed while the other end is closed using a removable end cap.

[0021] Components of an irradiation target assembly 1000 that do not actively participate in a nuclear reaction during an irradiation cycle may be configured to minimize any radiation originating therefrom after the irradiation cycle ends. In various instances, the outer tube 1100 and inner tube 1200 may be configured to minimize any radiation originating therefrom due to exposure to a neutron flux during an irradiation cycle of the irradiation target assembly 1000. For example, the outer tube 1100 and inner tube 1200 may each independently comprise a material (such as a zirconium-based alloy and / or a 316 series stainless steel). In instances where the irradiation target assembly 1000 includes a first end cap 1130 and / or a second end cap 1140, the end caps may comprise the same material as the outer tube 1100 and / or inner tube 1200. In some cases, this configuration of the irradiation target assembly 1000 may facilitate its handling, assembly, and / or disassembly before and / or after an irradiation cycle. Therefore, the irradiation target assembly 1000 can be configured to maintain safe operating conditions during its preparation and / or processing.

[0022] The terms "lateral alignment" and "lateral offset" herein refer to the position of a feature or structure relative to a specified axis in a plane perpendicular to that specified axis. For example, in a hexagonal prism whose height / length extends between two hexagonal faces, the specified axis may extend through the center of the hexagonal faces and a laterally offset feature may be positioned on that face at a distance from the center of the hexagonal faces. Similarly, the terms "radial alignment" and "radial offset" herein refer to the position of a feature or structure on or within a cylinder relative to the central longitudinal axis of that cylinder.

[0023] Referring again to FIG. 3, in an example where the first end 1110 is closed using a first end cap 1130, the first end cap 1130 includes an inner surface 1132 and a protrusion 1134 centrally located on the inner surface 1132. The cross-sectional geometry of the protrusion 1134 is sized to be substantially the same as or slightly smaller than the cross-sectional geometry of the inner surface 1102 near the first end 1110. Therefore, the first end cap 1130 can be inserted into the first end 1110 or otherwise coupled to the first end 1100 such that the radial center of the inner surface 1132 is aligned with the first axis of the outer tube 1100. In various embodiments, the first end cap 1130 and the inner surface 1102 near the first end 1110 can be configured to provide a reversible engagement therebetween to facilitate its removal from the outer tube 1100. For example, the periphery of the protrusion 1134 and the inner surface 1102 near the first end 1110 may include threads to screw the first end cap 1130 into the outer tube 1100. In other embodiments, the periphery of the protrusion 1134 and the inner surface 1102 near the first end 1110 may include complementary grooves to provide a rapid mechanical torsional coupling. Thus, this configuration of the outer tube 1100 facilitates the assembly and / or disassembly of the irradiation target assembly 1000. Therefore, in some embodiments, the irradiation target assembly 1000 may be configured to facilitate the reuse and / or recycling of its components in a subsequent irradiation cycle.

[0024] In an example where the first end 1110 is closed using a first end cap 1130, the first end cap 1130 engages the inner tube 1200 to form a first interface near the first end 1110. In various embodiments, the first end cap 1130 includes a protrusion 1136 extending inward from an inner surface 1132 for engaging an opening in one end of the inner tube 1200. The first interface may be configured such that the second axis of the inner tube 1200 is laterally aligned with the first axis of the outer tube 1100. For example, since the radial center of the inner surface 1132 is aligned with the first axis of the outer tube 1100 after the first end cap 1130 is coupled to the first end 1110, the lateral positioning of the first interface relative to the first axis of the outer tube 1100 when engaging one end of the inner tube 1200 will be determined by the radial positioning of the protrusion 1136 relative to the radial center of the inner surface 1132. Therefore, the position of the protrusion 1136 relative to the radial center of the inner surface 1132 can be configured to laterally align and / or offset the end of the inner tube 1200 participating in the first interface from the first axis of the outer tube 1100. In some instances, the protrusion 1136 is radially centered on the inner surface 1132, thereby providing a first interface that provides coaxial alignment between the central axis and the second axis. In some instances, the first end cap 1130 includes a geometry complementary to that of the inner tube 1200. For example, the end of the inner tube 1200 to be engaged by the protrusion 1136 may have a circular opening, and the protrusion 1136 may be configured to have a conical geometry that is at least partially insertable into the circular opening. The base of the conical protrusion 1136 may have a diameter larger than or substantially similar to the diameter of the circular opening. Therefore, in some configurations, the first end cap 1130 may be configured to facilitate the centering of the inner tube 1200 thereon by simply inserting the protrusion 1136 into the inner tube 1200.

[0025] In addition to the above, in an example where the second end 1120 is closed using a second end cap 1140, the second end cap 1140 may be configured similarly to the first end cap 1130. Therefore, the second end cap 1140 may be configured as a removable end cap and may include a protrusion 1146 to engage the inner tube near the second end 1120 to form a second interface. When combined with the first interface, the second interface may restrict axial movement of the inner tube 1200 while allowing axial movement of the inner tube 1200 after disassembly of the irradiation target assembly 1000. Therefore, the first and second interfaces between the inner tube 1200 and the first and second end caps 1130 and 1140 may maintain the axial and lateral positioning of the inner tube 1200 within the outer tube 1100, while maintaining the ability to easily remove the inner tube 1200 after disassembly of the irradiation target assembly 1000.

[0026] In various examples, the primary irradiation target material 1300 comprises a neutron trapping material configured to produce a quantitative emission based on exposure to a neutron flux (such as, for example, a thermal neutron flux within the core of an operating nuclear reactor) in a given irradiation cycle. In some examples, the primary irradiation target material 1300 is provided in particulate or powder form. The composition of the primary irradiation target material 1300 may be configured such that the emission to be produced comprises a photon emission, such as gamma radiation. For example, the primary irradiation target material 1300 may comprise thorium-157 and its oxides, which, after interacting with an incident neutron flux on the order of about 10¹³ neutrons / cm² / s, may emit gamma radiation with a high energy (such as greater than 6 MeV). Thus, in some forms, the primary irradiation target material 1300 may produce an emission suitable for the production of medical radioisotopes. In some examples, the primary irradiation target material 1300 comprises Gd₂O₃.

[0027] The secondary irradiation target material 1400 is configured to interact with an emission produced by the primary irradiation target material 1300. In an example where the primary irradiation target material 1300 is configured to emit a flux of high-energy photons (such as gamma radiation), the secondary irradiation target material 1400 may be configured to undergo a photonuclear reaction based on the interaction with the photon emission to provide a parent isotope of the desired isotope. The desired radioactive isotope will then be produced due to subsequent decay of the parent. In various examples, the secondary irradiation target material 1400 is configured to produce a parent isotope of actinium-225, such as radium-225. For example, the secondary irradiation target material 1400 may include radium-226, which can be converted to radium-225 after receiving a dose of gamma radiation. Subsequently, the natural decay of radium-225 produces a certain amount of actinium-225 as its decay product. In some instances, the secondary irradiation target material 1400 includes a salt of radium-226, such as radium nitrate (Ra2NO3).

[0028] Referring back to Figures 3 and 4, the inner tube 1200 includes an outer surface 1210 having an outer diameter. When surrounded by an inner surface 1102 of the outer tube, the outer surface 1210 and the inner surface 1102 define an intermediate cavity therebetween. In various embodiments, a secondary irradiation target material 1400 may be positioned within this intermediate cavity. In some embodiments, such as (for example) after the inner tube 1200 is positioned within the outer tube, the intermediate cavity is filled with the secondary irradiation target material 1400. In some embodiments, the secondary irradiation target material 1400 is used to occupy an entire volume defined by the intermediate cavity. The form of the secondary irradiation target material 1400 may be configured to facilitate its addition and / or removal. For example, the secondary irradiation target material 1400 may be provided in powder or granular form, which may be poured into and / or poured out of the intermediate cavity. The inventors of the present invention have determined that this configuration of the secondary irradiation target material 1400 may eliminate the need for an expansion gap.

[0029] The inner tube 1200 is configured to house the primary irradiation target material 1300, thereby positioning the primary irradiation target material 1300 radially inward toward any secondary irradiation target material 1400. In various embodiments, the inner tube 1200 defines an inner cavity in which a certain amount of the primary irradiation target material 1300 (such as Gd2O3 in powder form) is contained. In some embodiments, the inner tube 1200 containing the primary irradiation target material 1300 is prefabricated to facilitate its insertion and / or replacement. The inner tube 1200 includes a material substantially transparent to thermal neutrons (such as, for example, 316 series stainless steel) to allow a certain amount of the primary irradiation target material 1300 positioned therein to interact with an incident thermal neutron flux. Therefore, any emission to be produced by the primary irradiation target material 1300 is directed radially outward toward the secondary irradiation target material 1400, thereby increasing the possibility of interaction therebetween. In some configurations, this arrangement of the inner tube 1200 and its primary irradiation target material 1300 can optimize the delivery of an irradiation dose to a given amount of secondary irradiation target material 1400 relative to the total emission produced by the primary irradiation target material 1300 within a given time window. Therefore, the irradiation target assembly 1000 can be configured to minimize the amount of primary irradiation target material 1300 required to produce a desired amount of radioisotope from the secondary irradiation target material 1400 and / or the irradiation cycle time. Thus, incorporating the irradiation target assembly 1000 into a pharmaceutical radioisotope production process avoids premature depletion of the primary irradiation target material 1300 before the desired dose is delivered to the secondary irradiation target material 1400, thereby improving production efficiency, reducing material waste, and / or enhancing the efficacy of the pharmaceutical radioisotope.

[0030] In addition to the above, the dose delivered to the secondary irradiation target material 1400 can be tuned, for example, by changing the diameter ratio of the inner tube 1200 and the outer tube 1100. In one example, the inner tube 1200 is configured to have a cylindrical geometry containing an outer surface 1210 having an outer diameter of about 1.5 mm and centered within an inner surface 1102 having a diameter of about 4 mm and a length of about 50 mm, and the outer tube 1100 contains an inner surface 1102 having a diameter of about 4 mm. The inventors of the present invention have determined that an irradiation target assembly 1000 incorporated in this configuration can be used to irradiate at least 10 mg of a Ra2NO3-based secondary irradiation target material 1400 prior to depletion of a quantity of primary irradiation target material 1300 corresponding to about 100 mg of Gd-157 (such as, for example, about 115 mg of Gd2O3).

[0031] As discussed herein, an irradiation target assembly for producing a radioactive isotope is provided by the present invention. The irradiation target assembly includes an outer tube having a first end and a second end, an inner tube defining an inner cavity therein (containing a quantitative amount of internal neutron-capturing material including radium-157), a first end cap for the first end, and a second end cap for the second end. The inner tube is surrounded by the outer tube, both extending along a common central axis. Additionally, a volume enclosed between an outer surface of the inner tube and an inner surface of the outer tube thereby defines an intermediate cavity. An outer material (such as a target material including radium-226) is positioned within the intermediate cavity. The first end cap is removably attached to the first end of the outer tube, and the second end cap is removably attached to the second end of the outer tube. In various examples, the internal material including radium-157 is Gd₂O₃, and the target material including radium-226 is Ra₂NO₃. Therefore, the irradiated target assembly can be exposed to a neutron flux to produce a certain amount of actinium-225 without the need for excessive thiocyanate-157 to activate the external material.

[0032] The outer tube, inner tube, first end cap, and second end cap of the irradiation target assembly may be configured similarly to the outer tube 1100, inner tube 1200, and end caps 1130 and 1140, respectively, as described above. Therefore, the first end cap and the second end cap may be configured to maintain the axial and lateral positioning of the inner tube within the outer tube. In various embodiments, the outer tube and inner tube of the irradiation target assembly have a cylindrical geometry, thereby enclosing an annular shape and / or annular volume defining the intermediate cavity.

[0033] As discussed herein, a method for producing a radioactive isotope is provided by the present invention. In various instances, the method for producing a radioactive isotope includes exposing an irradiation target assembly to a neutron flux. This irradiation target assembly is similar in many respects to other irradiation targets and assemblies disclosed elsewhere in this invention, and for the sake of brevity, will not be repeated herein with the same level of detail. The irradiation target assembly to be exposed to the neutron flux includes an inner tube surrounded by an outer tube, both extending along a common central axis, wherein a volume enclosed between an inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity. The inner tube defines an inner volume therein containing a quantity of primary irradiation target material for generating an emission based on exposure to the neutron flux, and is surrounded by secondary irradiation target material contained within the intermediate cavity, the secondary irradiation target material interacting with the emission generated by the neutron-capturing material to produce the radioactive isotope. In various instances, the primary irradiation target material comprises thorium-157 and the secondary irradiation target material comprises radium-226. Therefore, the method according to the invention can be configured to produce actinium-225.

[0034] In various instances, the method according to the invention can be configured to reuse and / or recycle components of the irradiated target assembly after an irradiation cycle. For example, the method may include removing an end cap from one end of the outer tube, removing the radioisotope produced from the target material, and reusing the outer tube, the inner tube, or the end cap, or any combination thereof, in a subsequent production of the radioisotope. In some instances, the method includes decontaminating a disassembled component prior to reuse in the subsequent production of the radioisotope.

[0035] Various forms of the present invention include (but are not limited to) the forms listed in the following numbered items.

[0036] Clause 1 - An irradiation target for producing a radioactive isotope. The irradiation target includes an outer tube extending along a first axis and an inner tube extending along a second axis. The outer tube includes a first end, a second end, and an inner surface between the first end and the second end. The inner tube defines an inner cavity therein and includes an outer surface surrounded by the inner surface of the outer tube and a primary irradiation target material positioned within the inner cavity. The primary irradiation target material is configured to produce an emission based on exposure to a neutron flux. The inner surface of the outer tube and the outer surface of the inner tube define an intermediate cavity therebetween. The irradiation target further includes a secondary irradiation target material positioned within the intermediate cavity. The secondary irradiation target material is configured to interact with the emission produced by the primary irradiation target material to produce the radioactive isotope.

[0037] Item 2 – An irradiation target as described in Item 1, wherein the first end is closed with a first end cap and the second end is closed with a second end cap.

[0038] Item 3 – The irradiation target as described in Item 2, wherein the first end cap engages the inner tube to form a first interface near the first end, wherein the first interface aligns the second axis laterally relative to the first axis.

[0039] Clause 4 - An irradiation target as described in Clause 3, wherein the first interface provides coaxial alignment between the first axis and the second axis.

[0040] Clause 5 - An irradiation target as described in any of Clauses 3 or 4, wherein the first end cap includes a geometry complementary to the inner tube.

[0041] Clause 6 - An irradiation target as described in Clause 5, wherein the first end cap includes a conical section that is at least partially insertable into the inner tube.

[0042] Clause 7 - An irradiation target as described in any of Clauses 3 to 6, wherein the first end cap is removable.

[0043] Clause 8 - An irradiation target as described in any of Clauses 3 to 7, wherein the second end cap engages the inner tube to form a second interface near the second end, wherein the first interface and the second interface maintain an axial and lateral positioning of the inner tube within the outer tube.

[0044] Clause 9 - An irradiated target as described in any of Clauses 1 to 8, wherein the emission comprises a photon emission.

[0045] Clause 10 - An irradiated target as described in Clause 9, wherein the photon emission includes gamma radiation.

[0046] Clause 11 - An irradiation target as described in any of Clauses 1 to 10, wherein the primary irradiation target material comprises zirconia-157.

[0047] Item 12 - An irradiated target as described in any of items 1 to 11, wherein the neutron flux includes thermally splitting neutrons.

[0048] Clause 13 - An irradiation target as described in any of Clauses 1 to 12, wherein the radioactive isotope includes radium-225.

[0049] Clause 14 - An irradiation target as described in any of Clauses 1 to 13, wherein the secondary irradiation target material comprises radium-226.

[0050] Item 15 - An irradiation target as described in any of items 1 to 14, wherein the intermediate cavity is filled with the secondary irradiation target material.

[0051] Clause 16 - An irradiation target as described in Clause 15, wherein the secondary irradiation target material is used to occupy the entire volume defined by the intermediate cavity.

[0052] Clause 17 - An irradiation target as described in any of Clauses 1 to 16, wherein the dimensions of the irradiation target are configured to be installed within a flux sleeve of a nuclear reactor.

[0053] Clause 18 - An irradiation target assembly for producing a radioactive isotope. The irradiation target assembly includes an outer tube extending along a central axis, an inner tube extending along the central axis, a first end cap, a second end cap, and a target material. The outer tube includes a first end and a second end. The first end cap is used for the first end, and the second end cap is used for the second end. The inner tube defines an inner cavity therein, and a certain amount of radium-226 is accommodated within the inner cavity. The inner tube is surrounded by the outer tube, wherein a volume enclosed between an inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity. The first end cap and the second end cap are removably attached to the first end and the second end of the outer tube to maintain an axial and lateral positioning of the inner tube within the outer tube. The target material includes radium-226 and is positioned within the intermediate cavity.

[0054] Clause 19 – A method for producing a radioactive isotope. The method includes exposing an irradiation target assembly to a neutron flux. The irradiation target assembly includes an outer tube extending along a central axis and an inner tube extending along the central axis. The inner tube is surrounded by the outer tube. The inner tube includes a primary irradiation target material for generating an emission based on exposure to the neutron flux. A volume enclosed between an inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity. The irradiation target assembly further includes a secondary irradiation target material positioned within the intermediate cavity, wherein the secondary irradiation target material interacts with the emission generated by the primary irradiation target material to produce the radioactive isotope.

[0055] Clause 20 – The method of Clause 19, wherein the method further comprises removing an end cap from one end of the outer tube; removing the radioactive isotope produced from the target material; and reusing the outer tube, the inner tube, or the end cap, or any combination thereof, in a subsequent production of a radioactive isotope.

[0056] Various features and characteristics are described in this specification to provide an understanding of the composition, structure, manufacture, function, and / or operation of the invention, including the disclosed methods and systems. It should be understood that the various features and characteristics of the invention described in this specification can be combined in any suitable manner, whether or not such features and characteristics are explicitly described in this specification. The inventors and applicant expressly anticipate that combinations of such features and characteristics are included within the scope of the invention described in this specification. Therefore, the claims may be amended to describe any feature and characteristic explicitly or inherently described or otherwise explicitly or inherently supported by this specification in any combination. Furthermore, the applicant reserves the right to amend the claims to explicitly exclude features and characteristics that may exist in the prior art, even if such features and characteristics are not explicitly described in this specification. Therefore, any such amendments will not add new substances to the specification or claims and will comply with the requirements of written description, adequacy of description, and addition of substances.

[0057] As will be appreciated by those skilled in the art in relation to the appended claims, the operations therein can generally be performed in any order. Furthermore, although the various operational flows are presented in one (or several) sequence, it should be understood that the various operations can be performed in any order other than those depicted, or can be performed simultaneously. Unless the context otherwise indicates, examples of such alternative sequences may include overlapping, interleaving, interrupted, reordered, incremental, preparatory, supplementary, simultaneous, reverse, or other variations of the order. Moreover, terms such as "in response to," "related to," or other past tense adjectives are generally not intended to exclude such variations unless the context otherwise indicates.

[0058] The invention(s) described in this specification may include, consist of, or substantially consist of the various features and characteristics described in this specification. The terms "comprises" (and any form of "including", such as "comprises" and "comprising"), "has" (and any form of "has", such as "has" and "having"), "includes" (and any form of "includes", such as "includes" and "including"), and "contains" (and any form of "contains", such as "contains" and "containing") are open-ended linking verbs. Therefore, a method or system that "comprises", "has", "includes", or "contains" one or more features and / or characteristics has that feature or those features and / or characteristics, but is not limited to having only that feature or those features and / or characteristics. Similarly, "comprising," "having," "including," or "containing" means that a composition, coating, or process element has the feature or such feature and / or characteristic, but is not limited to having only the feature or such feature and / or characteristic and may have additional features and / or characteristics.

[0059] The grammatical articles “a” and “the” (as used in this specification (including the claims)) are intended to mean “at least one” or “one or more”, unless otherwise indicated. Therefore, articles are used in this specification to refer to one or more of the grammatical objects of the article (i.e., “at least one”). For example, “a component” means one or more components, and thus it is contemplated that more than one component may be used and employed or used in one embodiment of the described composition, coating, and process. However, it should be understood that the use of the terms “at least one” or “one or more” in some instances, but not in others, will not result in any interpretation limiting the objects of the grammatical articles “a” and “the” to only one. Furthermore, unless the context of use requires otherwise, a singular noun is used to include the plural, and a plural noun is used to include the singular.

[0060] In this specification, unless otherwise indicated, all numerical parameters in all examples shall be understood to be prefaced and modified by the term "about," wherein the numerical parameters have the variability inherent in the underlying measurement technique used to determine the value of the parameter. At least, and not at all, an attempt is made to limit the application of the equivalence criterion to the scope of the claims, each numerical parameter described herein shall be interpreted at least based on the number of significant figures reported and by applying general rounding techniques.

[0061] Any numerical range described herein includes all subranges covered within the stated range. For example, a range of "1 to 10" includes all subranges between (and inclusive of) the minimum value 1 and the maximum value 10, i.e., a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Furthermore, all ranges described herein include the endpoints of the range. For example, a range of "1 to 10" includes the endpoints 1 and 10. Any maximum numerical limit described in this specification is intended to include all smaller numerical limits covered therein, and any minimum numerical limit described in this specification is intended to include all larger numerical limits covered therein. Therefore, the applicant reserves the right to amend this specification (including the claims) to explicitly describe any subranges covered within the stated range. All such ranges are inherently described in this specification.

[0062] As used in this specification, especially when referring to layers, the terms "on," "to," "above," and variations thereof (e.g., "coated on," "formed on," "deposited on," "provided on," "located on," and the like) mean applied, formed, deposited, provided, or otherwise situated on one surface of a substrate but not necessarily in contact with the surface of the substrate. For example, a layer "applied on a substrate" does not exclude another layer or multiple layers of the same or different composition between the applied layer and the substrate. Similarly, a second layer "applied on a first layer" does not exclude another layer or multiple layers of the same or different composition between the applied second layer and the applied first layer.

[0063] Although specific examples of the invention have been described above for illustrative purposes, it will be apparent to those skilled in the art that numerous changes can be made to the details of the invention without departing from the invention as defined in the appended claims. [Simplified Explanation of the Diagram]

[0007] The various forms described herein, their purpose and advantages can be best understood by referring to the following description and the accompanying drawings.

[0008] Figure 1 is a partial cross-sectional view of a nuclear reactor core of at least one non-limiting state according to the present invention.

[0009] Figure 2 illustrates the gamma flux produced by an irradiated target material in at least one non-limiting state according to the present invention as a function of the depletion irradiation time of an irradiated target material.

[0010] Figure 3 illustrates a schematic diagram of an irradiation target of at least one non-limiting state according to the present invention.

[0011] Figure 4 shows a cross-sectional view of one of the irradiated targets in Figure 3.

[0012] Corresponding element symbols indicate corresponding portions throughout the various views. The examples set forth herein illustrate various aspects of the invention in one form, and such examples should not be construed as limiting the scope of any of the aspects disclosed herein.

Claims

1. An irradiation target for producing a radioactive isotope, the irradiation target comprising: An outer tube extending along a first axis includes: a first end; a second end; and an inner surface between the first end and the second end; an inner tube extending along a second axis, defining an inner cavity therein, wherein the inner tube includes: an outer surface surrounded by the inner surface of the outer tube, wherein the inner surface of the outer tube and the outer surface of the inner tube define an intermediate cavity therebetween; a primary irradiation target material positioned within the inner cavity, wherein the primary irradiation target material is configured to produce an emission based on exposure to a neutron flux; and a secondary irradiation target material positioned within the intermediate cavity, wherein the secondary irradiation target material is configured to interact with the emission produced by the primary irradiation target material to produce the radioactive isotope.

2. The irradiation target as claimed in claim 1, wherein the first end is closed with a first end cap and the second end is closed with a second end cap.

3. The irradiation target as claimed in claim 2, wherein the first end cap engages the inner tube to form a first interface near the first end, wherein the first interface aligns the second axis laterally relative to the first axis.

4. The irradiation target as claimed in claim 3, wherein the first interface provides coaxial alignment between the first axis and the second axis.

5. The irradiation target as claimed in claim 3, wherein the first end cap includes a geometry complementary to the inner tube.

6. The irradiation target as claimed in claim 5, wherein the first end cap includes a conical section that is at least partially insertable into the inner tube.

7. The irradiation target as requested in item 3, wherein the first end cap is removable.

8. The irradiation target of claim 3, wherein the second end cap engages the inner tube to form a second interface near the second end, wherein the first interface and the second interface maintain an axial and lateral positioning of the inner tube within the outer tube.

9. The irradiation target as claimed in claim 1, wherein the emission comprises a photon emission.

10. The irradiation target as claimed in claim 9, wherein the photon emission includes gamma radiation.

11. The irradiation target as claimed in claim 1, wherein the primary irradiation target material comprises zirconia-157.

12. The irradiation target as claimed in claim 1, wherein the neutron flux includes thermally splitting neutrons.

13. The irradiation target as claimed in claim 1, wherein the radiation isotope includes radium-225.

14. The irradiation target as claimed in claim 13, wherein the secondary irradiation target material includes radium-226.

15. The irradiation target of claim 1, wherein the intermediate cavity is filled with the secondary irradiation target material.

16. The irradiation target of claim 15, wherein the secondary irradiation target material is used to occupy the entire volume defined by the intermediate cavity.

17. The irradiation target of claim 1, wherein the dimensions of the irradiation target are configured to be installed within a flux sleeve of a nuclear reactor.

18. An irradiation target assembly for producing a radioactive isotope, the irradiation target assembly comprising: An outer tube extending along a central axis, the outer tube including a first end and a second end; an inner tube extending along the central axis, the inner tube defining an inner cavity therein, and a certain amount of radium-226 is accommodated within the inner cavity, wherein the inner tube is surrounded by the outer tube, wherein a volume enclosed between an inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity; a first end cap for the first end and a second end cap for the second end, wherein the first end cap and the second end cap are removably attached to the first end and the second end of the outer tube to maintain an axial and lateral positioning of the inner tube within the outer tube; and a target material positioned within the intermediate cavity, wherein the target material includes radium-226.

19. A method for producing a radioactive isotope, the method comprising: An irradiation target assembly is exposed to a neutron flux, the irradiation target assembly comprising: an outer tube extending along a central axis; an inner tube extending along the central axis, the inner tube including a primary irradiation target material for generating an emission based on exposure to the neutron flux, wherein the inner tube is surrounded by the outer tube, wherein a volume enclosed between an inner surface of the outer tube and an outer surface of the inner tube defines an intermediate cavity; and a secondary irradiation target material positioned within the intermediate cavity, wherein the secondary irradiation target material interacts with the emission generated by the primary irradiation target material to produce the radioactive isotope.

20. The method of claim 19, wherein the method further includes: Remove one end cap from one end of the outer tube; Remove the radioactive isotope produced from the secondary irradiated target material; and reuse the outer tube, the inner tube, or the end cap, or any combination thereof, in the subsequent production of one of the radioactive isotopes.

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