High-power point source converter-target assembly, associated equipment, and method for generating bremsstrahlung radiation for photonuclear reactions using an electron linear accelerator or electron accelerator with similar time structure of the beam

Abstract

The present invention relates to an installation for the production of radionuclides, more particularly diagnostic and therapeutic radionuclides, based on the principle of photonuclear irradiation, the installation comprising: an electron accelerator 1 for generating an electron beam 2 including time-structured characteristics for a linear electron accelerator 1; a converter target assembly 21 including a converter target 20 for converting the electron beam 2 into bremsstrahlung photons 15; a number of production targets 17 which are irradiated by said bremsstrahlung photons 15, thereby producing said radionuclides, The converter target assembly 21 includes a sealed housing 9, which includes: Surrounding a cavity 19 holding a converter target 20, an entrance window holder 8 including a mounted vacuum window disk 23 for the electron beam 2, and an exit window 22 for the bremsstrahlung photons 15, a coolant port 10 that is part of a cooling circuit 11 for establishing a cooling flow through the cavity 19, thereby cooling the converter target 20 and the vacuum window disk 23; The converter target 20 comprises several rotating converter disks 12, the electron beam 2 is offset relative to the respective converter disk 12; Each converter disk 12 is designed to rotate during operation of the installation, thereby causing the focus of the electron beam 2 to spread over a number of revolutions in an annular area 14 of the converter disk 12.

Description

[Technical Field]

[0001] The present invention relates to an apparatus for the production of radionuclides, more particularly diagnostic and therapeutic radionuclides, based on the principle of photonuclear irradiation. The present invention also relates to a converter target assembly for use in such an apparatus. The present invention further relates to a method for operating such an apparatus and a method for producing radionuclides. [Background technology]

[0002] Photonuclear reactions have been identified as being highly suitable for the production of diagnostic and therapeutic radionuclides for applications in nuclear medicine. High energy photons (≥ 8 MeV) can be used to induce nuclear reactions of the type (γ,n), (γ,2n), (γ,p), and (γ,pn). Photonuclear reactions exhibit significant cross sections in the giant dipole resonance (GDR) region, which in certain cases can be seen in the (proton, deuteron, 3 He and 4 The cross section for photonuclear reactions is not significantly smaller than that for charged particle-induced reactions (such as He). Due to the penetration characteristics of high-energy photons compared to charged particles, the total production yield of radionuclides by high-energy photons can be very high because the missing cross section compared to charged particle reactions can be overcompensated by a much thicker target. In general, the photonuclear cross section is roughly proportional to the atomic number.

[0003] Promising candidates for radionuclides that are in high demand and can be produced using photonuclear reactions are: 100 Mo(γ,n) reaction ( 99 Mo / 99m (for Tc radionuclide generators) 99 Mo or 66 Positron emitters for positron emission tomography produced by the Zn(γ,np) reaction 64 Cu. 111 The considerable activity of In is 112 Sn(γ,n) 111 Sn

number

[0004] A promising candidate for a radionuclide to be used for radionuclide therapy, which is not currently readily available but is in high demand and can be produced in high yields, is photonuclear reaction (PnR). 226 Formed by Ra(γ,n) 225 Alpha particle emitter (from the decay of Ra) 225 Ac, (reaction 68 Zn(γ,p)-produced beta-minus emitter 67 Cu, and (reaction 48 Ti(γ,p) 47 Sc. Furthermore, photonuclear reactions 150 Beta-minus emitter produced by Nd(γ,n) with a half-life of 53.1 h 149 Pm has promising chemical and decay properties as a therapeutic radionuclide. 90 Y or 177 Lu is, respectively, 91 Zr(γ,p) or 178 It can be produced in the Hf(γ,p) reaction. Summary of the Invention [Problem to be solved by the invention]

[0005] The underlying object of the present invention is to provide rare but highly sought-after radionuclides, in particular e.g. 225 Ac or 99 To provide a facility that allows industrial-scale production of diagnostic and therapeutic radionuclides, such as Mo. The facility should be cost-effective to construct and operate, with high reliability during operation, a high safety margin, and minimal consumption of raw materials. Furthermore, a converter target assembly for use in such a facility should be provided. Corresponding methods of operation and methods for production of radionuclides should also be provided. [Means for solving the problem]

[0006] According to the invention, the initially stated object is met by an arrangement according to claim 1.

[0007] The present invention provides an installation for the production of radionuclides, in particular diagnostic and therapeutic radionuclides, based on the principle of photonuclear irradiation, the installation comprising: an electron accelerator for generating an electron beam and, if necessary, a beam transfer line; a converter target assembly including a converter target for converting the electron beam into bremsstrahlung photons; a number of production targets which are irradiated by bremsstrahlung photons, thereby producing said radionuclides; The converter target assembly has a sealed housing, the housing comprising: Surrounding the cavity that holds the converter target, having an entrance window for the electron beam and an exit window for the bremsstrahlung photons, a coolant port that is part of a cooling circuit for establishing a cooling flow through the cavity, thereby cooling the converter target and the inlet window; The converter target has several rotating converter disks. The electron beam is offset from the center of each converter disk. Each converter disk is designed to rotate during operation of the equipment, thereby eventually spreading or dispersing the focal point of the electron beam over the annular area of ​​the converter disk.

[0008] In one aspect of the present invention, the electron accelerator is selected to generate an electron beam with a time structure characteristic of a linear electron accelerator. Such linear electron accelerators typically generate pulsed electron beams, which have an impact time ("beam-on time") in the microsecond range and a period time ("beam-off time") in the millisecond or longer range. In other words, "linear electron accelerator time structure characteristic" within the scope of the present invention should be understood as a pulsed time structure, where the total period time is significantly longer than the actual pulse time, resulting in a significantly "pulse"-like beam structure.

[0009] The present invention is based on the consideration that high yields of radionuclides of the above-mentioned type can be produced according to the principles of photonuclear irradiation when an electron beam having a relatively high electron energy and high beam power is guided onto a suitable point-source, high-power converter target to generate bremsstrahlung and then use the bremsstrahlung to irradiate a suitable production target. One key factor in enabling the converter target to withstand the heat load associated with such a high-intensity electron beam while maintaining the point-source nature of the resulting photon radiation is to distribute the beam energy over a relatively large area of ​​the converter target by rotating several stacked converter disks during irradiation, while simultaneously removing excess heat through a flow of cooling medium, particularly a cooling gas or liquid, in direct contact with the surface of the converter disks. The impact point or focal point of the electron beam is essentially fixed in space, while each converter disk moves relative to this fixed point, although some small deviations (compared to the target size) can be tolerated or even imposed.

[0010] Other mentioned objects are met by a converter target assembly according to claim 21 and by the corresponding method defined in claims 23 et seq.

[0011] Further features, embodiments, objects and related advantages are set out in the co-pending independent and dependent claims and the corresponding description in conjunction with the accompanying drawings.

[0012] In light of the preceding and following description, it is contemplated that the following non-limiting examples, many of which can be considered inventive in their own right.

[0013] 1. Installations for the production of radionuclides, in particular diagnostic and therapeutic radionuclides, based on the principle of photonuclear irradiation, an electron accelerator (1) for generating an electron beam (2) and, if necessary, a beam transfer line (3); a converter target assembly (21) including a converter target (20) for converting the electron beam (2) into bremsstrahlung photons (15); a production target (17) that is irradiated by bremsstrahlung photons (15) and thereby produces said radionuclides, The converter target assembly (21) comprises a sealed housing (9), the housing (9) comprising: Surrounding a cavity (19) that holds a converter target (20), an entrance window holder (8) including a mounted window disk (23) for the electron beam (2) and an exit window (22) for the bremsstrahlung photons (15), a coolant port (10) that is part of a cooling circuit (11) for establishing a cooling flow through the cavity (19) and thereby cooling the converter target (20) and the inlet window holder (8) including its attached window disk (23); The converter target (20) comprises several rotating converter discs (12), the electron beams (2) are offset relative to their respective converter disks (12); Each converter disk (12) is designed to rotate during operation of the equipment, thereby diffusing the focus of the electron beam (2) so that over time, over multiple irradiation cycles and converter disk rotations, a series of irradiation spots form a uniformly irradiated annular area of ​​the converter disk (12).

[0014] 2. An installation according to Example 1, in which the electron accelerator (1) is designed to generate electron energies exceeding 20 MeV.

[0015] 3. An installation according to example 1 or 2, in which the electron accelerator (1) is designed to generate a beam power exceeding 20 kW.

[0016] 4. An installation according to any of the preceding examples, in which an electron accelerator (1) generates a pulsed electron beam (2).

[0017] 5. An installation according to example 4, in which the pulsed electron beam (2) has an impact time of microseconds and a period time in the range of milliseconds or more.

[0018] 6. An installation according to Examples 4 or 5, in which the electron accelerator (1) is a linear accelerator or a microtron, or any other type of accelerator having a beam structure similar to those described in Examples 3 and 5.

[0019] 7. An installation according to Examples 4 to 5, in which the electron accelerator (1) is a superconducting linear accelerator.

[0020] 8. An installation according to any of Examples 4 to 7, comprising a control unit (24) that maintains the rotational speed of each converter disk (12) synchronized with the time structure of the electron accelerator.

[0021] The control unit preferably includes sensors, actors and controllers suitable for this task.

[0022] 9. An apparatus according to Example 8, in which the area on each converter disk exposed to a single beam pulse describes a substantially circular area, and the ratio of the converter disk revolution time to the cycle time is preferably selected so that the beam spot on the converter disk is rotated or displaced by at least one spot diameter. According to this aspect of the invention, the system is designed and engineered to limit the heat load deposited on the converter disk to an amount tolerable for the converter material. To facilitate this, in a preferred embodiment, the segment of the converter disk exposed to each beam pulse during each cycle time interval is moved so that it is not further exposed in subsequent pulses, or in other words, the segment is shifted or moved far enough so that subsequent electron pulses irradiate different segments. This concept, according to one aspect of the invention, allows for exposure of cooled portions of the converter disk with each pulse, so that over multiple irradiation cycles, a series of irradiation spots forms a substantially uniformly irradiated annular area of ​​the converter disk. Depending on the deposited energy per unit surface area on the converter disk, slight overlap in the deposition spots of subsequent beam pulses may be considered acceptable.

[0023] According to yet another aspect of the present invention, the converter disk may be rotated around two or more rotation axes, each substantially parallel to the beam direction. The rotation speeds around these various axes may be different, resulting in a wider ring area relative to the illuminated area on the converter disk. In particular, instead of providing only a single rotation axis, the design of the preferred embodiment may be extended with additional rotational or linear translation of the converter disk's primary rotation axis. In this way, the photon field is kept stationary, while an additional area of ​​the converter disk (compared to a single-axis design) is illuminated.

[0024] 10. An installation according to example 8 or 9, in which the rotational speed of each converter disk (12) is set within the range of several hundred to several thousand revolutions per minute.

[0025] 11. An installation according to any of the preceding claims, wherein the entrance window holder (8) has a rotating window disc (23), the electron beam (2) is set off-center relative to the window disc (23), and the window disc (23) is designed to rotate during operation of the installation, thereby gradually spreading the focus of the electron beam (2) over a plurality of irradiation spots on the window disc (23).

[0026] This is another important embodiment of the present invention, allowing for efficient heat distribution over a larger area of ​​the entrance window, similar to the converter disk. In one aspect of the present invention, depending on the deposited energy per unit surface area on the window disk (23), a small overlap of the deposition spots of subsequent pulses can be considered acceptable.

[0027] The window disc (23) is preferably mounted in / on / on a hollow shaft (30). Rotation of the hollow shaft (30) is preferably facilitated by a rotary drive (26).

[0028] 12. Installation according to example 11, in which the inlet window holder (8) is coupled to the rotary drive (26).

[0029] The rotary drive can be a stepper motor mounted on the outside of the housing, whereby the hollow vacuum feedthrough is driven by a gear drive.

[0030] 13. An installation according to Examples 11 or 12, in which the entrance window holder (8) has a window disk (23), which in a preferred embodiment is beryllium foil, preferably between 50 and 500 micrometers thick, or any other high-strength material with a low atomic number. In an alternative embodiment, the window disk (23) may be made of Havar™, preferably between 50 and 250 micrometers thick.

[0031] 14. An installation according to any of Examples 11 to 13, wherein the entrance window holder (8) is mounted on / in / to a hollow shaft that is part of a rotary vacuum feedthrough. In a preferred embodiment, the entrance window holder (8) and the attached window disk (23) or rotary vacuum feedthrough are sealed to the beam transfer line (3) by suitable feedthrough technology to separate the vacuum of the accelerator section from the gaseous or liquid cooling medium, preferably by a magnetic fluid seal (31).

[0032] 15. Installation according to example 14, in which the entrance window holder (8) and the attached window disk (23) are sealed to the beam transfer line (3) by a magnetic fluid seal. Alternatively, sealing can be achieved by any other feed-through technique to separate the vacuum of the accelerator part from the gaseous or liquid cooling medium.

[0033] Due to the required thin thickness of the inlet vacuum window and the mechanical and thermal stresses to which it is subjected, a preferred diameter of 40 mm was considered. Commercially available hollow shaft magnetic fluid sealed vacuum feedthroughs allow a maximum rotational speed of 3,100 rpm. Provisions for hollow shafts to be driven by gear drives are commercially available.

[0034] 16. An installation according to any of Examples 11 to 15, wherein the control unit (25) maintains the rotation speed of the entrance window holder (8) and the attached window disk (23) synchronized with the time structure of the electron accelerator.

[0035] 17. The area on each converter disk (12) exposed to a single beam pulse describes an approximately circular area, and the ratio of the revolution time of the converter disk (12) to the cycle time is preferably selected so that the beam spot on the converter disk is rotated by at least one spot diameter to allow exposure of cooled portions of the converter disk (12), and so that over multiple irradiation cycles and converter disk rotations, a series of irradiation spots forms a uniformly irradiated annular area of ​​the converter disk (12).

[0036] 18. An installation according to example 16 or 17, in which the rotation speed of the window disc (23) is set within the range of several hundred to several thousand revolutions per minute.

[0037] 19. An installation according to any of the preceding examples, wherein the beam transfer line (3) includes beam optical elements (5a-c) that enable focusing or defocusing of the electron beam (2) to different FWHMs.

[0038] 20. Installation according to example 19, with a FWHM of at least 2 mm.

[0039] 21. An installation according to any of the preceding examples, wherein the beam transfer line (3) includes beam wobblers (6, 7) that enable periodic movement of the focal point of the electron beam (2) on the entrance window foil (23) and on the respective converter disk (12).

[0040] 22. The installation according to example 21, wherein the wobble amplitude is in the range of millimeters on the converter disk (12).

[0041] 23. The wobble frequency is 10 1 From 10 6 Hz.

[0042] 24. An installation according to any of the preceding examples, wherein the beam transfer line (3) has a slammer valve (4) triggered by a downstream pressure sensor to protect the electron accelerator (1) from vacuum cracking of the converter target assembly (21).

[0043] 25. The apparatus according to any of the preceding examples, wherein the converter target (20) includes a plurality of converter disks (12).

[0044] 26. Installation according to example 25, in which the converter discs (12) are stacked on a common shaft (13).

[0045] Preferably, the converter disks are stacked or placed one on top of the other (concentrically) on the shaft with a gap between them to allow the coolant flow to cool any one of the disks from both sides, while keeping the gap small enough to keep the converter target compact and not destroy the all-important point source nature of the emerging photon radiation.

[0046] 27. An installation according to any of the preceding examples, wherein each converter disk (12) is coupled to a rotary drive (27).

[0047] The rotary drive is preferably mounted on the exterior of the housing in a shielded position. The converter disc is preferably driven by a stepper motor via a gear drive and rotary feedthrough.

[0048] 28. The installation according to any of the preceding examples, wherein the converter disc (12) is configured to form a Tesla pump.

[0049] 29. An installation according to any of the preceding examples, wherein the converter disc (12) is made primarily of tantalum or tungsten.

[0050] 30. An arrangement according to any of the preceding examples, wherein each converter disc (12) has a number of radially aligned slots or recesses in its outer periphery.

[0051] 31. An installation according to any of the preceding examples, wherein the exit window absorbs most of the photons with photon energies ≦8 MeV and preferably has a flattening filter (22) that absorbs and / or slows down the remaining electrons.

[0052] In one aspect of the present invention, and in a preferred embodiment, water is used as the cooling medium, in which case the water itself will function as such a flattening filter.

[0053] 32. The installation according to example 33, wherein the flattening filter (22) comprises a water-cooled aluminum column.

[0054] 33. An installation according to any of the preceding examples, wherein the exit window containing the flattening filter (22) contains a neutron absorber (16).

[0055] In one aspect of the present invention, and in a preferred embodiment, water is used as the cooling medium, in which case boric acid may be added to the cooling water to enhance neutron absorption.

[0056] 34. An installation according to any of the preceding examples, wherein the cooling medium is a liquid, preferably water. According to one aspect of the invention, a gas, preferably gaseous helium, may be used as the cooling medium.

[0057] 35. An installation according to any of the preceding examples, wherein a solid and preferably water-cooled beam stop (18) is arranged behind the production target (17).

[0058] 36. An installation according to any of the preceding examples in which the region of origin of emerging bremsstrahlung photons is fixed in space.

[0059] 37. An installation according to any of the preceding examples, in which the production target (17) is made primarily of one of the following isotopes: 226 Ra, 178 Hf, 150 Nd, 112 Sn, 100 Mo, 91 Zr, 66 Zn, 68 Zn, 48 Ti, 48 Ca.

[0060] 38. A converter target assembly (21) for installation according to any of the preceding claims, comprising a sealed housing (9), the housing (9) comprising: Surrounding a cavity (19) that holds a converter target (20), an entrance window holder (8) including an entrance window disk (23) mounted for the electron beam (2) and an exit window (22) for the bremsstrahlung photons, a coolant port (10) shown connected to a cooling circuit (11) for establishing a cooling flow through the cavity (19), thereby cooling the converter target (20) and the inlet window holder (8) including its attached inlet window disk (23); The converter target (20) has several rotating converter disks (12), each designed to rotate during operation of the equipment, thereby gradually spreading the focal spot of the incident electron beam (2) over multiple irradiation cycles in the converter target assembly (21). A series of irradiation spots forms a uniformly irradiated annular area of ​​the converter disk (12).

[0061] 39. A converter target assembly (21) according to Example 38, in which the entrance window holder (8) has a rotating window disk (23) that is designed to rotate during operation of the equipment, thereby, over time, spreading the focus of the incident electron beam (2) over multiple irradiation cycles. A series of irradiation spots forms a uniformly illuminated annular area of ​​the window disk (23).

[0062] 40. A method of operating equipment according to any of the preceding examples, wherein at least the following radionuclides are produced: 225 Ra, 224 Ra, 225 Ac, 213 Bi, 212 Pb, 177 Lu, 149 Nd, 149 Pm, 111 Sn, 111 In, 90 Y, 99 Mo, 99m Tc, 67 Cu, 64 Cu, 47 Ca, 47 Sc.

[0063] 41. A method for producing radionuclides, in which an electron beam (2) is directed onto a converter target (20), in particular comprising several rotating converter disks (12) around one or more axes, so that the focal point of the electron beam (2) is gradually spread over multiple irradiation cycles. The beam spot on the converter disks is rotated by at least one spot diameter to allow exposure of cooled portions of the converter disks (12), and over multiple irradiation cycles and converter disk rotations, a series of irradiation spots forms a uniformly irradiated annular area of ​​the converter disks (12). Depending on the deposited energy per unit surface area on the converter disks (12), slight overlap of the deposition spots may be acceptable. The generated beam of bremsstrahlung photons is used to irradiate the production target (17), and the converter target (20) is cooled by a flow of a cooling medium, in particular gaseous helium or, preferably, liquid water.

[0064] 42. A method according to Example 41, in which a converter target (20) is configured inside a housing (9), and an electron beam (2) is directed through a rotating entrance window holder (8) including an entrance window disk (23) attached to the housing (9) so that, over multiple irradiation cycles, a series of irradiation spots form a uniformly illuminated annular area of ​​the entrance window disk (23).

[0065] The detailed description of the present invention continues with reference to the accompanying drawings. [Brief explanation of the drawings]

[0066] [Figure 1] FIG. 1 is a schematic diagram of a photonuclear irradiation set-up assembly. [Figure 2] Schematic of a rotating hollow shaft vacuum feedthrough using a magnetic fluid seal. A vacuum window disk is mounted upstream of the rotating shaft. The beam axis is off-center relative to the rotation axis. [Figure 3]FIG. 1 shows a comparison of the time structure of an electron beam generated by a linear accelerator with that of an electron beam generated by a roadtron with similar beam power. [Figure 4] An exemplary illustration of a series of beam spots deposited on a rotating converter disk (e.g., 0.5 mm thick tungsten) is shown, where the time structure of the electron beam has beam-on periods in the microsecond range and beam-off periods in the millisecond range. The converter disk is rotated on a common shaft at an angular velocity that displaces the applied beam spot by at least one spot diameter. In this way, the available cooling time before a previously illuminated beam spot is illuminated again is maximized. Over time, an annular portion of the converter disk is illuminated. [Figure 5] The proposed scheme for irradiation of a rotating, e.g., beryllium (Be) vacuum window foil and a rotating converter disk, viewed in the direction of the beam axis. The window disk and the converter disk have minimal areal overlap and rotate in opposite directions. The tangential velocities of both disks are approximately the same to avoid excessive shear forces on the cooling medium, e.g., water. [Figure 6] Figure 1 shows a schematic diagram of a Tesla pump type rotating disk converter design. [Figure 7]This figure shows a technique involving further linear translation of the principal axis. In this figure, gray dots represent exemplary beam pulses. The blue line depicts the central location of the beam pulse hit on the disk. In subfigure a), a uniaxial design is shown. Here, the central spot line is the circumference of a circle with radius RC. Due to misalignment of the rotation frequency and beam repetition rate, the band between the virtual circles for RC+RBeam and RC-RBeam (gray dotted lines in the figure) is irradiated after several revolutions. In subfigure b), further vertical translation of the principal axis is introduced. This results in upward and downward oscillations for the central line spot, widening the irradiated area. The path of the central line describes an oscillatory motion with amplitude A1n around the mean radius RC. The figure depicts the path for approximately three revolutions. Care should be taken to detune the rotation frequency and the linear translation frequency. Otherwise, a stable trajectory is achieved, and only a portion of the total area between the virtual boundaries (gray dotted lines) is irradiated. DETAILED DESCRIPTION OF THE INVENTION

[0067] According to the present invention, the key to the industrial implementation of photonuclear reactions for medical radionuclide production are the following components: 1.) High-power electron accelerators with available electron energies greater than about 20 MeV and beam powers greater than about 20 kW. 2.) A high-power converter target that converts the electron beam into bremsstrahlung (braking radiation) photons that can absorb the power delivered by the high-intensity electron beam. The higher the photon flux in the GDR region, the higher the specific activity that can be reached (i.e., 99 Mo production) or production targets. Target material is mostly valuable isotopically enriched material (i.e., 67 For Cu generation 68 Zn) or preferably 225 Harmful highly radioactive materials for Ac generation (i.e.226 Ra). 3.) Able to withstand high energy and high intensity photon fluxes while safely and efficiently destroying hazardous and / or radioactive target materials (i.e. 226 A production target design that can contain Ra). 4.) Automated chemical procedures to extract the desired radionuclides in quality and quantity suitable for medical use.

[0068] Ad1): Several designs of electron accelerators have been developed in the past to generate bremsstrahlung radiation up to 10 MeV, primarily for the sterilization of medical devices or the curing of polymers. Currently, accelerators with beam energies of 30-40 MeV and beam powers of over 100 kW are commercially available. Ad2): High-power point-source converter targets capable of converting electron beams exceeding 20 MeV and beam powers exceeding 100 kW into bremsstrahlung have not been developed. This has effectively prevented the use of photonuclear reactions for the large-scale production of medical radionuclides. The description of such converter targets is a major topic of current applications. Ad3): Current methods are up to the task because the target material can be encapsulated in a relatively thick, high strength, high temperature material. Ad4): For many of the radionuclides mentioned above, chemical separation procedures for separating the desired products from the target material have already been developed or can be adapted from existing procedures.

[0069] Based on the evaluation presented above, the design and construction of a high-power converter target is crucial to generate bremsstrahlung radiation for photonuclear reactions. The crucial preferred components, their functions and their technical realization are sketched in attached drawing 1 and described below.

[0070] FIG. 1 shows schematically a preferred assembly of a photonuclear irradiation suite comprising a high-power electron beam 2 provided by a conventional (non-continuous wave) linear electron accelerator or electron accelerator (i.e., microtron) 1 with a similar time structure of the beam, a vacuum beam line 3, a fast-acting vacuum valve 4 (slammer valve) located within the beam line 3, several beam optical elements (5a-c) for focusing or defocusing the beam 2 to different full width half maximum (FWHM), a rotating vacuum window holder 8 including a rotating vacuum window disk 23, a rotary drive 26 for the vacuum window including an associated control unit 25, a housing 9 for a rotating converter target 20, and provisions, i.e., inlet and outlet ports 10 for supplying a cooling medium flowing through the housing 9, and the converter target 20 including several (here one) rotating converter disks 12 surrounded by the housing 9. Also shown are the distributed beam spot 14 (trace over time) on the rotating converter disk 12, the rotation axis 13 of the converter disk 12 coupled to a rotary drive 27 including an associated control unit 24, the emergence cone 15 of bremsstrahlung photons, the flattening filter and neutron absorber 16, the generation target 17 and the bulk high density beam stop 18.

[0071] As will be apparent from FIG. 1 and the detailed description below, a vacuum window holder 8 including a mounted vacuum window disk 23 disposed within the housing 9 serves as an inlet or entrance window for the electron beam 2 entering a cavity 19 enclosed by the housing 9. The electron beam 2 impinges on a converter target 20 disposed within the cavity 19, generating bremsstrahlung photons 15. A flattening filter 22 and a neutron absorber 16 disposed within the housing 9 serve as an outlet or exit window 22 for the photon cone 15 exiting the cavity on the other side. The photon cone 15 is centered on the extension of the electron beam axis. The cavity 19 is sealed by the housing 9 in a liquid-tight manner against the external environment. That is, the entrance window 8 and the flattening filter exit window 22 provide a liquid-tight barrier while remaining generally transparent to electron or photon radiation, respectively. A flow of cooling medium, particularly cooling water, within cavity 19 provides cooling to converter target 20 and also to vacuum window holder 8, which includes rotating vacuum window disk 23, by flowing over the interior surfaces of cavity 19. This cooling flow enters and exits cavity 19 by way of cooling medium inlet and outlet ports 10 located in the housing wall. The housing wall may be further cooled by a flow of cooling liquid, particularly cooling water, through suitable flow paths.

[0072] The cooling flow through cavity 19 is part of the cooling circuit 11, which is only shown diagrammatically in Figure 1. Advantageously, liquid water is used as the cooling medium. The pressure of the cooling medium inside cavity 19 is preferably in the range of atmospheric pressure in order to maintain within manageable limits the pressure difference between the inlet window 8 and the flattening filter outlet window 22.

[0073] As will be appreciated in more detail below, the rotation axis 13 of the converter disk 12 is arranged off-center (shifted parallel) with respect to the axis of the electron beam 2 .

[0074] Furthermore, the entrance window holder 8 for the electron beam 2 preferably comprises a rotating window disk 23 whose axis of rotation is also arranged off-center (shifted parallel) with respect to the axis of the electron beam 2 .

[0075] The unit comprising a housing 9 including cooling inlet and outlet ports 10, a vacuum window holder 8 including an attached vacuum window disk 23 for the entrance of the electron beam 2, a flattening filter 22 and neutron absorber 16 at the exit of the photon cone 15, and an integral converter target 20 - including, if required, an associated rotary drive for the vacuum window holder 8 including the vacuum window disk 23 and / or the converter target 20 - may be referred to as a converter target unit or converter target assembly 21.

[0076] Instead of a single flattening filter 22 and neutron absorber 16, there may be two (or more) separate filters, one for flattening (see below) and one for neutron absorption. It is convenient for these functions to be integrated into a single exit window 22 of the housing 9, but in addition to the exit window 22 for high-energy photons, there may also be several additional filters of the kind described above, integrated into one assembly or realized as separate components. For example, there may be a simple exit window 22 that seals the housing 9 in a leak-tight manner against the outside environment, then a flattening filter and a neutron absorber in any order (when viewed in the direction the photons pass through), or only one or neither of the latter.

[0077] When using a liquid coolant, especially flowing water, as a coolant, the coolant itself already acts as a flattening filter, absorbing mainly low-energy bremsstrahlung radiation (<8 MeV) that does not contribute to the photon nucleation process. Furthermore, the addition of boric acid to the coolant enhances its neutron absorption properties.

[0078] More specifically, an industrial radionuclide production facility using a photonuclear reaction preferably comprises: ·High power electron linear accelerators or electron accelerators with similar time structure of the beam. An evacuated beam transfer line that transports the extracted electron beam through a vacuum. A fast acting valve (slammer valve), preferably containing a downstream pressure sensor, to protect the accelerator from vacuum breakdown. Preferably a beam optical element that allows focusing or defocusing of the beam to different FWHM, for example in the form of a quadrupole triplet. A beam optical element called a "beam wobbler" that allows rapid movement of the beam in the x and y directions, preferably at high frequencies. · Vacuum windows that separate the accelerator and beam line vacuum from the converter target assembly. Housing containing converter target assembly. Provisions and connections for cooling gas and / or liquid. A cooled converter target assembly that stops the electron beam (ideally completely) and converts it into bremsstrahlung photons of various energies. The converter target preferably has several disks, thereby reducing their individual heat loads and configured in an optimal manner for efficient cooling. By rotating the converter disk, preferably in synchronization with the time structure of the beam, the incident beam packet is distributed uniformly over a large area of ​​the converter disk. Preferably, a flattening filter that absorbs most of the low-energy photons that contribute only to heating the production target but do not induce photonuclear reactions. This task can be accomplished simultaneously by using a liquid coolant as a cooling medium. A neutron filter, preferably for low and high energy photoneutrons that contribute to the production of unwanted by-products, thus increasing the purity of the radionuclide of the desired product. A cooled assembly holding at least one production target, preferably a stack of multiple production targets, and preferably a means for remotely adding or retrieving production targets. · (Optional) A cooled block of beryllium for generating photoneutrons. Cooled bulk beam stop including auxiliary (optional) irradiation position for precious stone coloring. A cooling loop, preferably including a pump, reservoir, heat exchanger, and filter, for cooling the converter target assembly.

[0079] Figure 2 shows a schematic of the rotating vacuum window assembly. An electron beam 2 impinges on an off-center beryllium vacuum window disk 23. The beryllium vacuum window disk is mounted in a ring-like holder 8 attached to a rotating hollow shaft vacuum feedthrough 30. Alternatively, the holder 8 may be an integral part of the hollow shaft 30. On the left, the rotating vacuum window assembly is connected to the beam transfer line 3. On the right, there is a cavity 19. The hollow shaft 30, with its magnetic fluid seal 31 and bearings 32, separates the accelerator 1 and beam transfer line 3 vacuum from the housing 9 coolant. If a coolant is used, any suitable technique for separating the coolant from the beam line vacuum can be used. The hollow shaft is driven by a rotary drive 26 and corresponding control unit 25 (shown schematically in Figure 1).

[0080] In the following sections, preferred embodiments and basic concepts of the individual components are described in more detail.

[0081] 1) Electron beam accelerator and specifications Electron accelerators suitable for inducing photonuclear reactions must satisfy several requirements regarding electron beam energy, beam intensity (beam power), beam time structure, and beam spatial width. Several types of accelerators are currently commercially available that can deliver electron beams with energies greater than 20 MeV and beam powers exceeding 20 kW, which are necessary conditions for producing useful radionuclides for medical applications.

[0082] Commercially available linear accelerators have electron energies between 35 MeV and over 100 MeV, with maximum beam powers between 35 kW and 120 kW. Peak current intensities of 200 mA to 300 mA are available with variable repetition rates, e.g., 800 Hz, resulting in average beam currents of up to 4 mA. Pulse lengths can be up to 16 μs [1a]. The electron beam can be shaped to different FWHMs by the use of beam optics. The beam profile can be selected to be non-Gaussian (i.e., flat-top profile).

[0083] Rhodotron-type accelerators with electron energies of 40 MeV and maximum beam powers of 125 kW are commercially available. Rhodotron accelerators operate at 10 Hz to 50 Hz with duty cycles of 1% to 12.5%, resulting in pulse lengths of up to 2.5 ms with a maximum peak current intensity of 25 mA and an average beam current of 3.125 mA [1b]. The electron beam can be shaped to different FWHMs by the use of beam optical elements. The beam profile can be selected to be non-Gaussian (i.e., flat-top profile).

[0084] Compared to a roadtron, a conventional linear accelerator is advantageous when operated with a point-source converter target. Due to the different beam structure, the beam pulse is much shorter compared to a roadtron. Therefore, the beam power cannot be significantly spread over the larger area of ​​the vacuum window and the rapidly moving components of the converter assembly. However, the short beam-on pulse results in the deposited energy of one pulse being approximately the same areal energy density (cm of vacuum window or converter disk assembly). 2 In particular, for a flat-top beam profile with a 5 mm diameter (delivered by a 40 MeV, 800 Hz, 125 kW linear accelerator), the energy density deposited on a 0.5 mm thick tungsten converter disk is approximately 10-15 J / cm.2 The energy density (approximately 10 J / cm) delivered by a 2.5 ms duration, 5 mm diameter, flat-top beam profile, roadtron (40 MeV, 50 Hz, 125 kW) beam-on pulse reached 100 mW, spread over one-third of the area of ​​a rotating 0.5 mm thick converter disk at a radius of 15 cm. 2 ) is approximately the same. Therefore, the peak temperature per beam pulse induced by the passage of an intense electron beam is similar. This situation is illustrated schematically in Figure 3.

[0085] More specifically, Figure 3 shows a comparison of the time structure of the electron beam generated by a linear accelerator with that of the electron beam generated by a rodetron. In this example, the linear accelerator was assumed to generate beam pulses of 15 μs duration and a peak current of 200 mA at a pulse repetition rate of 800 pps. This results in an average beam current of 2.4 mA at a 1.2% duty cycle. The rodetron was operated at 50 Hz and generated beam pulses of 25 mA peak current and 2.5 ms duration. This results in an average beam current of 3.125 mA at a 12.5% ​​duty cycle.

[0086] 2) Fast acting valve (slammer valve) To protect the accelerator and beam line from vacuum window cracking and material migration into the accelerator cavity, a fast-acting valve triggered by a pressure sensor placed in front of the vacuum window and downstream of the beam line is installed. In case of vacuum window cracking, the fast-acting valve physically closes the cross section of the beam line within milliseconds before the front of the penetrating shock wave reaches the accelerator.

[0087] 3) Rotating vacuum window and converter target synchronization with the beam structure In the presented approach, a fixed beam spot is guided onto a rotating disk (vacuum window or converter target). The revolution times of these components are synchronized with the beam structure to distribute the heat load over the disk. In particular, the beam structure of a linear electron accelerator (LINAC) is characterized by a very short beam-on pulse, on the order of microseconds, followed by a beam-off period, on the order of milliseconds. Although the beam-on period is very short, it is characterized by a very high beam current, on the order of hundreds of milliamperes. Meanwhile, the beam-off period, on the order of milliseconds, allows the rotation of the vacuum window and converter disk so that previously cooled areas of the vacuum window or converter disk are irradiated. This means that the window and converter disks must be rotated by at least one beam diameter during the beam-off period to expose a new, cooled portion of the window or converter disk before the next beam pulse. In this way, the rotation speed of the window and converter disks can be significantly reduced from several thousand rotations per minute, which is required for a lordotron beam time structure, to several hundred rotations per minute, which is required for a conventional LINAC beam time structure. For illustrative purposes, the illumination pattern is depicted in FIG.

[0088] More specifically, Figure 4 shows an example of a pattern generated by applying short microsecond beam pulses with a frequency of several hundred Hz to a rotating disk. With a repetition rate of 800 Hz and a beam diameter of 5 mm, and beam pulses applied to a 15 cm radius on the converter disk, a maximum of 188 positions can be generated when the wheel is rotated at 255 revolutions per minute. This results in a maximum cooling time per deposition spot of 235 ms, significantly longer than the cooling time for irradiation of a one-third circumference section using a rodotron, where the cooling time is only 60 ms. Depending on the beam diameter, the rotation speed can be adjusted to a faster rotation speed to prevent overheating of adjacent deposition spots. Alternatively, if overlapping of deposition spots is acceptable, i.e., with a Gaussian beam profile, the rotation speed can be further adjusted to a slightly slower rotation speed. The generally lower rotation speed (several hundred rpm vs. several thousand rpm in the rodotron irradiation case) allows the use of a liquid cooling medium such as water.

[0089] 4) Vacuum window The electron beam from the accelerator must pass through a vacuum window that separates the accelerator vacuum from the converter's cooling circuit. This window must withstand the electron beam intensity without compromising its mechanical stability. Therefore, the window must be made of a low-atomic-number material with a high melting point, good mechanical strength, and a low atomic number to allow the electron beam to pass through with significantly less energy loss. Furthermore, the vacuum window material should be relatively chemically inert and not react with the components or trace elements of the cooling circuit. Suitable materials for the vacuum window are foils made from beryllium or some high-strength alloys (e.g., Havar™). The vacuum window and converter target material must be cooled due to the energy deposited by the intense electron beam. Blackbody radiation is overwhelmingly insufficient to dissipate the deposited energy.

[0090] Vacuum windows made from beryllium foils with thicknesses greater than 0.1 mm have been investigated. The energy deposited on the foil depends on the foil thickness, but does not exceed 80 watts for a 100 μm thick window.

[0091] Assuming a 5 mm beam diameter (flat-top profile), the temperature rise for one beam pulse from a conventional linear electron accelerator (40 MeV, 800 Hz, 125 kW) passing through a 0.1 mm thick beryllium window was calculated to be only 1.5 °C. To further reduce temperature variations, the entrance vacuum window can be rotated (see Figure 6). That is, the vacuum window is coupled to a rotary drive. As an example, a 4 cm diameter Be foil is mounted on a hollow shaft that is part of a rotary vacuum feedthrough, preferably using a magnetic fluid seal. A commercially available 4 cm rotary vacuum feedthrough can be rotated at a maximum speed of approximately 3100 rpm. In our study, the beam struck the periphery of a 4 cm diameter disk at a distance of 0.5 cm from the edge, resulting in a 3 cm diameter annular impact zone.

[0092] Assuming a 5 mm deposition spot, approximately 18 spots can be applied to the rotating vacuum window disk. For a 1.25 ms beam-off period, the vacuum window disk needs to be rotated at approximately 2600 rpm. This rotation speed can be reduced if a smaller beam diameter or overlapping of deposition spots is acceptable. This aspect becomes important when liquid cooling is considered. The resulting cooling period is on the order of 20 ms before a new beam spot is applied, which should be long enough to allow complete cooling of the applied beam spot. The temperature rise per beam spot is relatively low, and a thicker beryllium window provides greater mechanical strength, so a smaller beam diameter or overlapping of deposition spots can be tolerated.

[0093] More specifically, Figure 6 shows a schematic of a 4 cm diameter Be foil mounted on the hollow shaft of a rotary vacuum feedthrough, cooled on one side by flowing He gas or water.

[0094] The rotation speed was chosen to be 2,600 rpm. In this way, about 18 deposition spots were formed, each spot being illuminated for a few microseconds, followed by a 1.25 ms beam-off period, during which the disk was rotated by about one beam spot diameter. This resulted in a 20 ms cooling period before the same spot was illuminated again.

[0095] More specifically, Figure 5 shows the irradiation of a rotating Be foil vacuum window in the proposed scheme. The foil rotates in the opposite direction (counterclockwise) compared to the rotation direction of the converter disk. The proposed scheme, with a beam configuration at 800 Hz and 1.2% duty cycle, maximizes the cooling period of the irradiated area. By minimizing the areal overlap between the window disk and the converter disk (as viewed in the direction of the beam axis) as much as possible and by rotating the window disk and the converter disk in opposite directions, the tangential velocities of the rotating window disk and the converter disk are approximately the same, thereby minimizing the generation of shear forces on the cooling medium, especially water.

[0096] 5) Electronics, housing, and cooling for the photon converter The electron beam then strikes the converter material. The converter must be a material with a high melting point and good mechanical stability. Furthermore, the material must be of high atomic number and high density to effectively convert the electron beam into bremsstrahlung. High atomic number and high density contribute to optimal point-source generation of bremsstrahlung. For maintenance and radioactive waste management reasons, the converter material should only be slightly activated by the electron beam. Furthermore, the converter material should be relatively chemically inert and not react with components or trace elements of the cooling circuit. The thickness of the converter must be adapted to the range of electrons in the converter material. A good converter material is tungsten or tantalum, 4 to 5 mm thick.

[0097] The interaction of electrons with the converter material can be described by a number of physical processes, but is quite complex. For the production of radionuclides in photonuclear reactions, bremsstrahlung photons with energies above approximately 8 MeV are important. However, to consider the energy deposited in the converter material, all physical processes must be included. What is important is the configuration of the converter material in relation to the irradiated target material. Bremsstrahlung photons greater than 8 MeV are emitted mainly in the forward direction (beam direction) in the form of a cone with a certain divergence angle.

[0098] The vacuum window and converter target material must be cooled due to the energy deposited by the powerful electron beam. Blackbody radiation is far too insufficient to dissipate the deposited energy. Therefore, the vacuum window and converter must be cooled by a gas or liquid. In our discussion, cooling by flowing helium gas is proposed. Helium has the advantage of being a material with high viscosity and low atomic number, which cannot be activated or degraded by bremsstrahlung photons. In the case of water as a coolant, photonuclear reactions involving oxygen isotopes have occurred. Most notably, 16 O(γ,n) 15A relatively short-lived isotope with a half-life of 122.24 s in the O reaction 15 The other possible reaction products are: 13 N(T 1 / 2 =9.97m), 11 C(T 1 / 2 =20.364m), or 14 C(T 1 / 2 =5730a). 14 With the exception of C, these products are short-lived and can be filtered out of the cooling water ( 15 (Except O.)

[0099] Similar principles that apply to the construction of vacuum window assemblies can be applied to converter targets. As discussed above, the converter must be a high-Z, high-melting-point material and provide good thermal conductivity. The converter must achieve mechanical stability for high-speed rotation and only need to be activated very slightly. Our considerations lead us to choose tantalum as the converter material due to its high melting point of 3017°C and its machinability. Furthermore, natural tantalum consists of only two isotopes: tantalum and tantalum, with a natural abundance of 99.98799%. 181 Ta and 0.01201% natural abundance 180m Ta. 181 For the (γ,n) or (γ,2n) reaction on Ta, respectively, 180 Ta itself, or stable with a half-life of 665 days 179 Become Hf 179 The latter decays by electron capture without gamma radiation. It has a half-life of 8.15 h. 180 The formation of Ta requires further investigation, but its decay may lead to a stable 180 W or stable 180 In the (γ,pxn) reaction on Ta, stable Hf isotopes are formed. 182 The formation of Ta is expected to contribute only to minor activation of the Ta converter material.

[0100] Furthermore, tungsten can be considered a good converter material due to its high melting point of 3422°C. Furthermore, natural tungsten consists of five isotopes, namely, tungsten with a natural abundance of 0.12%. 180 W, natural abundance 26.50% 182 W, natural abundance 14.31% 183 W, natural abundance 30.64% 184 W, and natural abundance of 28.43% 186 It consists of W. 180 The (γ,n) or (γ,2n) reaction on W decays to a stable γ with a half-life of 665 days, respectively. 179 Become Hf 179 Ta, or collapse 178 Relatively short-lived 178 W(T 1 / 2 =22d) to form either one of them. 182 W and 183 The (γ,n) or (γ,2n) reaction involving W has a half-life of 121.2 days. 181 W is formed, which decays by electron capture under the radiation of X-rays and very low energy gamma rays to form stable 181 It becomes Ta. 186 The (γ,n) reaction with W has a half-life of 75.1 days. 185 W is formed, which decays with low branching ratios by beta-minus radiation (0.4 MeV) and 125 keV gamma rays to form stable 185 It becomes Re. 183 W and 184 In the (γ,p) or (γ,pn) reaction involving W, the half-life is 114.43 d. 182 The formation of Ta needs to be investigated, as its dose rate contributes significantly to the total dose rate, even after an extended decay period. Of less interest are the (n,γ) reactions for the various W isotopes. In general, W has many advantageous properties as a converter material, but its activation is expected to be much higher than for Ta.

[0101] The converter target assembly should be very compact, allowing a high photon flux with minimal divergence angles. The ideal thickness for the generation of gamma rays in the energy window from 8 to 30 MeV is between 4 mm and 5 mm.

[0102] To distribute the approximately 45 kW energy deposition within a 4.5 mm thick W converter slab, the converter target is divided into multiple disks. The energy of the beam pulses, a few microseconds in length, is distributed around the circumference of the rotating disk, which is assumed to have a radius of 15 cm. As discussed above, the disk rotation speed is preferably synchronized with the beam's time structure, resulting in a rotation speed of over 255 rpm for a beam diameter of 5 mm and a deposition radius of 15 cm.

[0103] The number of discs can be increased while the overall thickness is adjusted to an optimum value between 4.5mm and 5mm.

[0104] The maximum temperature reached depends on the FWHM of the electron beam. The energy deposited in a practical converter reaches approximately 45 kW. To remove this heat, a helium gas flow of approximately 250 L / s is required at standard temperature and pressure (STP), assuming a helium gas exit temperature 200°C higher than the entrance temperature. This fairly high helium flow rate can be achieved with a commercially available, medium-sized pump. Alternatively, a water flow can be considered for cooling. The energy deposited in the window, converter disk, and cooling water reaches approximately 50 kW. Assuming an inlet temperature of 20°C and an exit temperature of 80°C, a minimum cooling water flow of 200 ml / s (12 L / min) is required, which is easily achieved with a commercially available water pump. Furthermore, the rotating converter disk assists the cooling flow by acting as a Tesla pump.

[0105] The converter disks are stacked on a common shaft, separated by small gaps (on the order of millimeters or less). The number of disks and their thickness are optimized for the electron beam energy to achieve maximum bremsstrahlung conversion efficiency. As discussed above, the disks rotate at a speed that preferably moves the deposited beam spot by at least one diameter of the spot during the beam-off period. Rotational speeds of hundreds to thousands of rpm have been achieved, depending on the diameter of the converter disk and the diameter of the beam spot. The disks are sealed in a water-cooled housing with a small gap between the disk and the wall. To cool the disks, which are heated by the particle beam as described above, a cooling gas (e.g., helium) is circulated through the gap between the disks. Due to the low rotational speed, water can also be used as a cooling medium. In this case, water cooling of the housing is no longer required. An orifice concentric with the shaft is foreseen to facilitate axial gas or liquid flow along the shaft. The housing incorporates openings to allow gas or liquid circulation from the outer edge of the disk. This configuration describes an adhesion-type pump, also known as a Tesla pump, which was originally described in US Pat. No. 1,061,206, which is incorporated herein by reference.

[0106] The gas or liquid flow between the disks spirals (vortices) due to the interaction of the gas or liquid with its adhesion to the disks and its internal viscosity. The rotation increases the contact time of the gas or liquid with the disk surfaces, optimizing heat transfer to the refrigerant. In a pump configuration, the shaft is externally driven and the gas or liquid flows from the shaft toward the outer edges of the disks.

[0107] The outward flow of cooling gas or liquid allows for uniform cooling of the disks. Furthermore, as the number of disks increases, the total surface area available for cooling increases. The total heat load of the system in this configuration remains constant, but the load per disk can be lowered.

[0108] More specifically, Figure 6 shows a diagram of the Tesla converter design. On the left, the entire disk assembly is shown, including the shaft and multiple disks, and the (blue) particle beam impinges on the disks near their outer edges (showing heated areas corresponding to the circular trace of the electron beam). On the right, a sketch of the refrigerant flow pattern on a single disk is drawn for a pump-configured converter.

[0109] 6) Reduction of energy density Further reduction of the energy density at the converter disk can be achieved by further movement of the main axis or further movement (deflection) of the electron beam. While the first approach maintains the essentially point-like nature of the emerging photon beam, deflection of the electron beam results in a reduced photon density at the location of the generation target. Figure 7 shows an approach with further linear movement of the main axis (or vertical deflection of the beam). In this figure, the grey dots represent exemplary beam pulses. The blue line depicts the central location of the beam pulse spot on the disk. In subfigure a), a uniaxial design is shown. Here, the central spot line has a radius R C Due to misadjustment of the rotation frequency and beam repetition rate, the radius R C +R Beam The virtual circumference and R C -R Beam The zone between the imaginary circumference of and (gray dotted line in the figure) is irradiated after a few revolutions. The irradiated area is given by A rot =π[(R C +R Beam ) 2 -(R C -R Beam ) 2 ].

[0110] In subfigure b), a further vertical movement of the main axis (or vertical deflection of the beam) is introduced. This results in an upward and downward oscillation of the central line spot, which increases the illuminated area. The path of the central line has an average radius R C Centered on amplitude Alin The diagram depicts the oscillatory motion of the ion beam. The diagram depicts the path for approximately three revolutions. Care should be taken to detune the frequency of rotation from the frequency of linear translation. In other cases, a stable orbit is achieved and only a portion of the total area between the imaginary boundaries (gray dotted lines) is illuminated. The illuminated area is quantified by A rot / lin =π[(R C +R Beam +A lin ) 2 -(R C -R Beam -A lin ) 2 ].

[0111] Linear actuation of the main axis of rotation (or vertical deflection of the beam) is the simplest extension of this method. It is certainly possible to achieve circular motion of the main axis.

[0112] 7) Generation Target The target material must be located within the emergence cone of photons to be effectively illuminated. If the amount of target material is limited (i.e., 226 Ra, or, but not limited to, 48 Ca, 48 Ti, 68 Zn, 100 Mo, 112 Sn, or 150 The target (highly isotopically enriched material such as Nd) must be placed as close as possible to the converter. The close geometric configuration of the converter achieves the highest possible photon flux density. 100 From Mo 99 Mo generation increases the target material 100 "Carrier added" that cannot be chemically separated from Mo 99 Mo is obtained from this material. 99m To facilitate production, a Tc radionuclide generator is used. 99 The specific activity of Mo should be greater than about 5 Ci / g of Mo. This is due to the high density photon flux and the highly concentrated100 This can only be achieved by irradiation of Mo, provided that the photons emerge from a point such as the converter source. Photons with an energy of 8 MeV or higher are highly penetrating, so stacks of target materials can be irradiated simultaneously. During irradiation, the target material absorbs the photons and the energy is deposited in the target. The target must therefore be cooled, for example by flowing cooling water. High photon energy has the advantage that target materials that are difficult to handle due to their radioactivity, toxicity, or chemical reactivity can be safely contained in materials suitable for irradiation. This prevents cracks in the target material from entering the cooling water circuit. Furthermore, simultaneous irradiation of several production targets with the same photon beam can be carried out, thereby allowing the simultaneous production of several radionuclides. For example, relatively thin 226 Ra is added where the photon flux is highest closest to the converter assembly, followed by, for example, a high production rate but relatively expensive concentrating material. 112 Sn or 150 Nd, and 68 Zn or 48 A bulk target of Ti follows, although chemical separation and regeneration procedures already exist when handling large amounts of target material. Preferably, provisions are made to remotely load, unload, and transport the target to the processing high temperature cell.

[0113] 8) Block beam stop Most of the high-energy photons penetrate all target materials and must be stopped by a solid, preferably water-cooled beam stop, i.e., made of lead. According to Figure 8, the energy deposited in the beam stop amounts to about 68 kW [2]. For shielding, one can imagine a vertical configuration of the electron beam, converter, and production target, with the ground as additional shielding around the solid beam stop. Otherwise, additional shielding (i.e., concrete) must be put in place to reduce the gamma radiation dose to acceptable levels.

[0114] Inside the bulk beam stop, it is possible to foresee a means of irradiating artificial precious stones: high-energy gamma radiation induces defects in the lattice of artificially grown precious stones, which act as color centers, allowing for the permanent coloring of artificially grown precious stones such as topaz.

[0115] 9) Cooling circuit The low rotational speed allows the use of water as the coolant, which greatly facilitates the construction of a suitable cooling circuit. The required water flow is modest, and most components are commercially available. Therefore, the technical simplicity far outweighs its activation by the particle beam. Assuming an inlet temperature of 20°C and an outlet temperature of 80°C, a minimum cooling flow of 200 ml / s (12 L / min) of water is required, which is easily achieved with commercially available water pumps. Furthermore, the rotating converter disk assists the cooling flow by acting as a Tesla pump. Chillers capable of removing heat on the order of 100 kW or more are available for building air conditioning units.

[0116] Alternatively, helium gas may be selected as the cooling medium due to its low atomic number and density, its chemical inertness, and its reasonable heat capacity. Furthermore, helium does not react with high-energy bremsstrahlung photons. Assuming a temperature increase of 200°C, approximately 250 L / s of helium at STP would be required to remove the energy deposited within the converter target assembly. It is anticipated that helium gas will enter the converter assembly at room temperature. Helium gas is preferably circulated in a gas loop. Therefore, the cooling circuit preferably includes a high-flow pump, a high-flow heat exchanger, a reservoir tank, filters for trace components such as oxygen, water vapor, and particles, and a means for filling and emptying the circuit with helium gas. The pressure in the helium tank (high-pressure side) can be regulated by a butterfly valve connected to a pressure sensor. Some components of the cooling circuit, such as a high-flow interchiller or radial compressor, can be sourced from the automotive industry.

[0117] Calculated yields of radionuclides (examples): Using a point source high power converter-target assembly as described above, and a production target exposed to the resulting photon field, and assuming an electron energy of 40 MeV and a beam power of 125 kW, the following yields can be obtained:

[0118] 226 From Ra 225 Generation of Ra: 100mg / cm 2 With a target thickness of 10.65 GBq and a target diameter of 2 cm, 225 The production rate of Ra / day was calculated, which is the rate after an ingrowth period of 14 to 15 days. 225 This corresponds to about 5 GBq of Ac. To limit the number of chemical separation steps, it is advantageous to choose a longer irradiation time, for example 2 weeks. After a waiting period of several days, 225 The first batch of Ac can be separated from the irradiated target. Shortly thereafter, with an optimal waiting time of about 17 days, the half-life of 14.9 days is reached.225 Due to the fall of Ra 225 Thanks to Ac's internal growth, the so-called second and third opportunities 225 Assuming such a production regime and a patient dose of 10 MBq, one 226 Approximately 500 patient doses per day can be generated from the Ra target.

[0119] 100 From Mo 99 Mo generation: 1g / cm 2 With a target thickness of 1.0 and a target diameter of 2 cm, the target yield is approximately 650 GBq. 99 The production rate of Mo / day was calculated, which corresponds to approximately 17.5 Ci / day / target. 2 In this case, the target thickness is still relatively thin.

[0120] The calculated yields indicate that photonuclear reactions are a practical production method for medical radionuclides. The point-source high-power converter-target assembly described above can absorb enormous beam powers of up to 125 kW, enabling routine radionuclide production using linear electron accelerators.

[0121] References: The following references are incorporated herein by reference: [1a] MEVEX Accelerator Technologies Company. High-Power Linear Accelerators (Linacs) for Isotope Production. http: / / www.mevex.com / Brochures / Brochure_High_Energy.pdf [Accessed May 17, 2019] [1b] Ion Beam Applications, IBA Industrial, Rhodotron® TT300-HE High Energy Electron Generator, www.iba-industrial.com [Accessed June 26, 2018] [2] M. Vagheian, "A Point Source High Power Converter Target to Produce Bremsstrahlung for Photonuclear Reaction," PhD thesis, University of Bern, Switzerland, February 25, 2022. [Explanation of symbols]

[0122] 1. Electron beam source (electron accelerator) 2. Electron beam 3 Electron beam transfer line (vacuum pipe) 4. Vacuum valve (slammer valve) 5a~c Beam optical elements (quadrupole triplet) 8 Inlet window holder for vacuum window 9. Housing 10 Coolant Ports (Inlet and Outlet Ports) 11 Cooling loop (cooling circuit) 12 Converter Discs 13 Rotation axis 14 Projected focal beam spot (trace in time) 15 Bremsstrahlung photon cone (photon field) 16 Neutron absorber 17 Generation Targets 18 Beam Stop 19 Cavity 20 Converter Targets 21 Converter Target Assembly 22 Flattening filter / exit window 23 Vacuum window disk 24 Vacuum window control unit 25 Converter disk control unit 26 Vacuum window rotary drive 27 Converter Disc Rotary Drive 30 hollow shaft 31 Magnetic fluid seal 32 bearings 33 Rotation axis

Claims

1. 1. An installation for the production of radionuclides, in particular diagnostic and therapeutic radionuclides, based on the principle of photonuclear irradiation, comprising: an electron accelerator (1) for generating an electron beam (2) including time-structured characteristics for a linear electron accelerator (1); a converter target assembly (21) including a converter target (20) for converting the electron beam (2) into bremsstrahlung photons (15); several production targets (17) that are irradiated by said bremsstrahlung photons (15) and thereby produce said radionuclides; Equipped with The converter target assembly (21) comprises a sealed housing (9), said housing (9) comprising: - Encloses a cavity (19) that holds a converter target (20); - has an entrance window including a window disk (23) for said electron beam (2) and an exit window (22) for said bremsstrahlung photons (15), - having a coolant port (10) that is part of a cooling circuit (11) for establishing a cooling flow through the cavity (19), thereby cooling the converter target (20) and the window disk (23); The converter target (20) comprises several rotating converter discs (12), the electron beams (2) are offset relative to their respective converter disks (12); Each converter disk (12) is designed to rotate during operation of the installation, thereby eventually spreading the focus of the electron beam (2) over a number of revolutions in an annular area (14) of the converter disk (12).

2. 2. The installation according to claim 1, wherein the electron accelerator (1) generates a pulsed electron beam (2), the pulsed electron beam (2) having an impact time in the range of microseconds and a period time in the range of milliseconds or more.

3. 3. The installation according to claim 1 or 2, comprising a control unit (24) for maintaining the rotational speed of each converter disk (12) synchronized with the periodic time structure of the electron beam.

4. 4. The installation of claim 3, wherein the area on each converter disk (12) exposed to a single beam pulse describes an approximately circular area, and the ratio of the revolution time of the converter disk (12) to the periodic time of the electron beam (2) is preferably selected so that the beam spot on the converter disk is rotated by at least approximately one spot diameter.

5. 5. The installation according to claim 1, wherein the rotational speed of each converter disc (12) is set within the range of several hundred to several thousand revolutions per minute.

6. 6. The installation according to claim 1, wherein the window disk (23) is rotatable and held or supported by an entrance window holder (8), the electron beam (2) is set off-center with respect to the window disk (23), and the window disk (23) is designed to rotate during operation of the installation, thereby gradually spreading the focus of the electron beam (2) over a plurality of irradiation spots on the window disk (23).

7. 7. The installation of claim 6, wherein the entrance window holder (8) has or holds a preferably circular window disk (23), preferably beryllium foil or any other high strength material with a low atomic number, and the entrance window holder (8) is mounted on / in / to a hollow shaft (30) that is part of a rotary vacuum feedthrough or is part of a hollow shaft (30).

8. 8. The installation according to claim 7, wherein the entrance window holder (8) and the attached window disk (23) or the rotary vacuum feedthrough is sealed to the beam transfer line (3) by a magnetic fluid seal (31).

9. 9. The installation according to any one of claims 6 to 8, wherein a control unit (25) keeps the rotation speed of the entrance window holder (8) and the attached window disk (23) synchronized with the time structure of the electron beam period time.

10. 10. The installation according to claim 9, wherein the area on the window disk (23) exposed to a single beam pulse describes an approximately circular area, and the ratio of the revolution time of the window disk (23) to the beam period time is preferably selected so that, over multiple irradiation cycles, a series of irradiation spots forms a uniformly illuminated annular area of ​​the window disk (23).

11. 11. Installation according to any one of claims 6 to 10, wherein the rotation speed of the window disc (23) is set within the range of several hundred to several thousand revolutions per minute.

12. 12. An arrangement according to any one of claims 6 to 11, wherein the overlap of the window disc and the rotating converter disc is minimal when viewed along the beam axis.

13. 13. The installation according to any one of claims 6 to 12, wherein the direction of rotation of the window disc (23) is opposite to the direction of rotation of the rotary converter disc.

14. 14. The installation according to any one of claims 1 to 13, wherein the beam transfer line (3) comprises beam optical elements (5a-c) that allow focusing or defocusing of the electron beam (2) to different FWHMs ("full width at half maximum"), with a FWHM of at least 2 mm being set.

15. 15. The installation according to any one of the preceding claims, wherein the converter target (20) comprises a plurality of preferably circular converter discs (12).

16. 16. The installation according to claim 15, wherein the converter discs (12) are stacked on a common shaft (13).

17. 17. The installation according to any one of claims 1 to 16, wherein each converter disc (12) is coupled to a rotary drive (27).

18. 18. The installation according to any one of claims 1 to 17, wherein the converter disc (12) is configured to form a Tesla pump.

19. 19. The installation according to any one of claims 1 to 18, wherein the cooling medium is a cooling liquid, in particular water.

20. 20. The installation according to any one of claims 1 to 19, wherein apart from some optional vibrations or some movements of the common shaft (13) with amplitudes in the millimeter range, the region of generation of emerging bremsstrahlung photons (15) is fixed in space.

21. A converter target assembly (21) for an installation according to any one of claims 1 to 20, comprising a sealed housing (9), said housing (9) comprising: - Encloses a cavity (19) that holds a converter target (20); an entrance window holder (8) with a mounted entrance window disk (23) for the electron beam (2) and an exit window (22) for the bremsstrahlung photons, - having a coolant port (10) shown connected to a cooling circuit (11) for establishing a cooling flow through the cavity (19), thereby cooling the converter target (20) and the inlet window holder (8) including its attached inlet window disk (23); The converter target (20) comprises a number of rotating converter disks (12), each designed to rotate during operation of the equipment, thereby eventually spreading the focus of an incident electron beam (2) over a series of approximately circular beam spots, which form a uniformly irradiated annular area of ​​the converter disk (12) over multiple irradiation cycles and rotations of the converter disk, forming a converter target assembly (21).

22. 22. The converter target assembly (21) of claim 21, wherein the entrance window holder (8) has a rotating window disk (23) that is designed to rotate during operation of the equipment, thereby gradually spreading the focus of the incident electron beam (2) over a series of approximately circular beam spots that form a uniformly illuminated annular area of ​​the window disk (23) over multiple irradiation cycles and rotations of the window disk.

23. A method for producing radionuclides, in which an electron beam (2) is guided onto a converter target (20) comprising several rotating converter disks (12) in such a way that the focal point of said electron beam (2) is spread over the annular area of ​​each converter disk (12), thereby generating a beam of bremsstrahlung photons (15) for irradiation of a production target (17), said converter target (20) being cooled by a flow of a cooling medium, in particular gaseous helium or liquid water.

24. 24. The method according to claim 23, wherein the converter target (20) is configured inside a housing (9) and the electron beam (2) is directed through a rotating entrance window holder (8) including the attached entrance window disk (23) of the housing (9) such that the focal point of the electron beam (2) is spread over a series of substantially circular beam spots, the series of substantially circular beam spots forming a uniformly illuminated annular area of ​​the entrance window disk (23) over a number of irradiation cycles.

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