High-power converter-target assembly for producing bremsstrahlung for photonuclear reactions, related equipment and methods

Abstract

An apparatus for the production of a radionuclide based on photonuclear irradiation, comprising: an electron accelerator 1 for generating an electron beam 2; a converter target assembly 21 including a converter target 20 for converting the electron beam 2 into bremsstrahlung photons 15; and a production target 17 which is irradiated by the bremsstrahlung photons 15, thereby producing said radionuclide.

Description

[Technical field]

[0001] 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 present invention also relates to a converter target assembly for use in such an installation. The present invention further relates to a method for operating such an installation and to 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 types (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 are (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 penetrating properties of high energy photons compared to charged particles, the total production yield of radionuclides by high energy photons can be much higher 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 emitter for positron emission tomography produced by the Zn(γ,np) reaction 64 Cu. Furthermore, 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 that is not currently readily available, but is in high demand and can be produced in high yields, is photonuclear nuclei (PnN). 226 It is formed by Ra(γ,n) 225 Alpha particle emitter (from the decay of Ra) 225 Ac, (Reaction 68 Zn(γ,p)) beta-negative emitter 67Cu, 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Pat. No. 1,061,206 Summary of the Invention [Problem to be solved by the invention]

[0006] The underlying object of the present invention is to provide a method for the production of rare but highly sought-after radionuclides, in particular e.g. 225 Ac or 99The objective of the present invention is to provide a facility enabling industrial-scale production of diagnostic and therapeutic radionuclides, such as Mo. The facility should be cost-effective to build and operate, with high reliability during operation, high safety margins, and minimal consumption of raw materials. Furthermore, converter-target assemblies for use in such facilities should be provided. Corresponding methods of operation and methods for production of radionuclides should also be provided. [Means for solving the problem]

[0007] According to the invention, the initially stated object is met by an arrangement according to claim 1.

[0008] The present invention provides an installation for the production of radionuclides, in particular diagnostic and therapeutic radionuclides, based on the principle of photonuclear irradiation, comprising: an electron accelerator for generating the electron beam and, if necessary, the 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: - Encloses a cavity that holds the converter target, having an entrance window for the electron beam and an exit window for the bremsstrahlung photons, having 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 off-centered with respect to each converter disk. Each converter disk is designed to rotate during operation of the equipment, thereby causing the focal point of the electron beam to spread or disperse over the annular area of ​​the converter disk.

[0009] The invention is based on the consideration that high yields of radionuclides of the above-mentioned kind can be produced according to the principle of photonuclear irradiation, if an electron beam with a relatively high electron energy and high beam power is guided onto a suitable point source, high power converter target, generating bremsstrahlung and then irradiating a suitable production target with bremsstrahlung. One important factor that allows the converter target to withstand the heat load associated with such a high intensity electron beam, while at the same time maintaining the point source character of the emerging 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 at the same time removing the excess heat by a flow of a cooling medium, in particular a cooling gas, 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 some small deviations (compared to the target size) can be tolerated or even imposed, while each converter disk moves relative to this fixed point.

[0010] Other mentioned objects are met by a converter target assembly according to claim 22 and by the corresponding method defined in claims 24 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. 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) 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) which is irradiated by bremsstrahlung photons (15) and thereby produces said radionuclide, The converter target assembly (21) has a sealed housing (9), the housing (9) including: - Enclosing a cavity (19) which 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), 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 inlet window holder (8) including its attached window disk (23); The converter target (20) has several rotating converter disks (12), The electron beams (2) are offset from each other relative to the respective converter disks (12), Each converter disk (12) is designed to rotate during operation of the installation, thereby, in time, spreading the focal spot of the electron beam (2) over an 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 in excess of 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 of more than 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) or a continuous wave electron beam (2).

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

[0018] 6. An installation according to example 4 or 5, in which the electron accelerator (1) is a roadtron.

[0019] A rhodotron is an electron accelerator based on the principle of recirculating a beam through successive diameters of a single coaxial cavity resonating at metre waves. After one acceleration phase, the beam is redirected back into the cavity by magnets. The emergence pattern resembles the arrangement of petals on a rose flower (from the Greek word "rhodon" for rose, due to the rosette-like particle paths).

[0020] 7. An installation according to Examples 4 to 5, in which the electron accelerator (1) is a superconducting linear accelerator.

[0021] 8. An installation according to any of the embodiments 4 to 7, comprising a control unit (24) for maintaining the rotational speed of each converter disk (12) synchronized with the time structure of the electron beam pulses.

[0022] The control unit preferably includes sensors, actors and controllers suitable for this task.

[0023] For example, the rotational speed of a Tesla turbine (see below) can be controlled by controlling the pressure difference between the tangential input nozzle and the outlet, thereby controlling the gas velocity interacting with the converter disc.

[0024] 9. An installation according to Example 8, in which the area on each converter disk (12) exposed to a single beam pulse describes a complete ring (14) or a sector thereof, and the ratio of the revolution time of the converter disk (12) to the beam pulse time is preferably selected such that all sectors are uniformly irradiated over multiple irradiation cycles.

[0025] 10. An installation according to example 8 or 9, wherein the rotational speed of each converter disk (12) is set within the range of several thousand to several tens of thousands of revolutions per minute.

[0026] Ideally, one beam pulse interval would map to one full revolution, but in practice the maximum rotation speed may be limited by the stress or burst resistance of the converter disk material under high centrifugal forces.

[0027] 11. Installation according to any of the preceding claims, wherein the inlet window holder (8) has a rotating window disc (23), the electron beam (2) is set off-centre with respect to the window disc (23), and the window disc (23) is designed to rotate during operation of the installation, thereby in time spreading the focus of the electron beam (2) over an annular area of ​​the window disc (23).

[0028] This is another important embodiment of the present invention and allows efficient heat distribution over a larger area of ​​the inlet window, similar to a converter disk.

[0029] The window disc (23) is preferably mounted in / on / a hollow shaft (30). Rotation of the hollow shaft (30) is preferably facilitated by a rotary drive (26).

[0030] 12. An installation according to example 11, in which the inlet window holder (8) is coupled to a rotary drive (26).

[0031] The rotary drive can be a stepper motor mounted on the outside of the housing, whereby a hollow magnetic fluid sealed vacuum feedthrough is driven by a gear drive.

[0032] 13. An installation according to Examples 11 or 12, in which the inlet window holder (8) has a window disk (23) which is beryllium foil or any other high strength material with low atomic number.

[0033] 14. An installation according to any of Examples 11 to 13, wherein the inlet window holder (8) is mounted on / within / on a hollow shaft that is part of the rotary vacuum feedthrough.

[0034] 15. An 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.

[0035] Due to the required thin thickness of the inlet vacuum window as well as the mechanical and thermal stresses to which it is exposed, 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.

[0036] 16. An installation according to any of Examples 11 to 15, wherein a control unit (25) keeps the rotational speed of the entrance window holder (8) and the attached window disk (23) synchronized with the time structure of the electron beam pulses.

[0037] 17. An installation according to Example 16, in which the area on the window disk (23) exposed to a single beam pulse describes a complete ring or a sector thereof, and the ratio of the revolution time of the window disk (23) to the beam pulse time is preferably selected such that all sectors are uniformly irradiated over multiple irradiation cycles.

[0038] 18. An installation according to Examples 16 or 17, wherein the rotation speed of the window disc (23) is set within the range of several hundred to several thousand revolutions per minute.

[0039] In theory, the window disk could rotate as fast as the converter disk, ideally mapping one beam pulse interval to one full revolution, but in practice, currently available vacuum feedthroughs limit the maximum rotation speed.

[0040] 19. An installation according to any of the preceding examples, wherein the beam transfer line (3) includes optical elements (5a-c) enabling focusing or defocusing of the electron beam (2) to different FWHM.

[0041] 20. Installation according to example 19, with a FWHM of at least 2 mm.

[0042] 21. The beam transfer line (3) comprises a beam wobbler (6, 7) enabling periodic movement of the focal point of the electron beam (2) on the entrance window foil (23) and on the respective converter disk(s) (12), in accordance with any of the preceding examples.

[0043] 22. The installation according to example 21, wherein the wobble amplitude is in the millimeter range on the converter disk(s) (12).

[0044] 23. Wobble frequency is 10 1 From 10 6 Hz.

[0045] 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).

[0046] 25. An installation according to any of the preceding examples, wherein the converter target (20) includes a plurality of converter disks (12), in particular four converter disks (12).

[0047] 26. Installation according to example 25, in which the converter discs (12) are stacked on a common shaft (13).

[0048] Preferably, the converter disks are stacked or placed one on top of the other (concentrically) on the shaft with a gap between them so that the cooling medium flow can cool any one of the disks from both sides, while the gap is small enough to keep the converter target compact and not destroy the vital point source character of the emerging photon radiation.

[0049] 27. An installation according to example 25, in which the converter disks (12) are arranged one after the other on parallel shafts, but in succession, so as to overlap partially when viewed in the direction of the shafts.

[0050] 28. An installation according to examples 26 or 27, in which each shaft (13) is aligned parallel to the direction of the electron beam (2).

[0051] 29. An installation according to any of the preceding examples, wherein each converter disk (12) is coupled to a rotary drive (27).

[0052] The rotary drive is preferably mounted externally to the housing in a shielded position. The converter disc is preferably driven by a stepper motor via a gear drive and rotary feed-through.

[0053] 30. The arrangement of any of the preceding examples, wherein the converter disk (12) is configured to form a Tesla pump.

[0054] 31. An installation according to any of the preceding examples, wherein the converter disc (12) is designed to be driven by a cooling flow.

[0055] This generally implies some sort of turbine configuration: for example, the converter disk may be coupled to an axial or radial turbine placed in the cooling flow.

[0056] 32. The installation according to example 31, wherein the converter disk (12) is configured to form a Tesla turbine.

[0057] Thus, in essence, each converter disc forms a turbine in itself.

[0058] The Tesla turbine is a bladeless centripetal flow turbine patented by Nikola Tesla in 1913. It is called a vaneless turbine.

[0059] Tesla turbines are also known as boundary layer turbines, adhesion-type turbines, or Prandtl layer turbines (after Ludwig Prandtl) because they use the boundary layer effect rather than the fluid impinging on blades as in conventional turbines.

[0060] The Tesla turbine contains a set of smooth disks with nozzles that impinge the moving fluid on the edges of the disks. The viscosity and adhesion of the surface layer of the fluid causes the fluid to be dragged over the disks. As the fluid slows down and adds energy to the disks, it spirals into a central discharge. The rotor has no protrusions, making it extremely sturdy. It can reach extremely high rotational speeds, up to tens of thousands of revolutions per minute.

[0061] 33. Installation according to examples 31 to 32, in which the rotational speed of the converter disc (12) is controlled by the tangential flow velocity of the cooling flow using a differential pressure regulator.

[0062] 34. An installation according to any of the preceding examples, wherein the converter disc (12) is made primarily of tantalum or tungsten.

[0063] 35. 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.

[0064] 36. An installation according to any of the preceding examples, wherein the exit window absorbs most of the photons with photon energy ≦8 MeV and preferably has a flattening filter (22) that absorbs and / or slows down the remaining electrons.

[0065] 37. The installation according to example 36, wherein the flattening filter (22) includes a water-cooled aluminum column.

[0066] 38. An installation according to any of the preceding examples, wherein the exit window including the flattening filter (22) includes a neutron absorber (16).

[0067] 39. An installation according to any of the preceding examples, wherein the cooling medium is a cooling gas.

[0068] 40. Installation according to Example 39, in which the cooling gas is helium.

[0069] 41. An apparatus according to any of the preceding examples, in which a solid, and preferably water-cooled, beam stop (18) is arranged behind the production target (17).

[0070] In addition to the production of radionuclides, the present invention further relates to a method of operating such equipment for use in producing photoneutrons as an electron accelerator based neutron source. The photoneutrons produced may have a variety of applications in different fields of science and engineering, such as materials characterization, nuclear science, neutron photography, and may offer several advantages over reactor based neutron sources, including the problem of radioactive waste management. A high yield of photoneutrons can be achieved by directing an electron beam with relatively high electron energy and high beam power onto a suitable point source, high power electron photon converter target (first converter target) to generate bremsstrahlung, which is then used to convert the bremsstrahlung radiation into a neutron ( 9 Be(γ,n) 8 Photoneutrons can be produced according to the principle of photonuclear irradiation when irradiating suitable elements (second converter targets) such as one (or more) thick beryllium targets as photoneutron converter targets (through the Be reaction). Thus, the present invention provides an installation for the production of high yields of photoneutrons using two (or more) types of converter target materials in a set of new innovative converter target assemblies based on the principle of photonuclear reactions.

[0071] 42. An installation according to any of the preceding examples, in which the region of occurrence of emerging bremsstrahlung photons is fixed in space, apart from some optional deflections having an amplitude in the range of millimeters.

[0072] 43. The production target (17) is mainly composed of the following isotopes: 226 Ra, 178 Hf, 150 Nd, 112 Sn, 100 Mo, 91 Zr, 66 Zn, 68 Zn, 48 Ti, 48 An installation according to any of the preceding instances, made in one of the Ca.

[0073] 44. A converter target assembly (21) for installation according to any of the preceding claims, comprising a sealed housing (9), the housing (9) comprising: - Enclosing a cavity (19) which holds a converter target (20); an entrance window holder (8) including 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 to be 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 several rotatable converter disks (12), each of which is designed to rotate during operation of the installation, thereby, in time, spreading the focus of the incident electron beam (2) over the annular area of ​​the converter disks (12), forming a converter target assembly (21).

[0074] 45. Converter target assembly (21) according to example 44, in which the entrance window holder (8) has a rotating window disk (23) that is designed to rotate during operation of the equipment, thereby eventually spreading the focus of the incident electron beam (2) over an annular area of ​​the window disk (23).

[0075] 46. ​​At least the following radionuclides: 225 Ra, 224 Ra, 225 Ac, 213 Bi, 212 Pb, 177 Lu, 149 Nd, 149 Pm, 111 Sn, 111 In, 90 Y, 99 Mo, 67 Cu, 64 Cu, 47 Ca, 47A method of operating an installation according to any of the preceding examples, in which Sc is generated.

[0076] 47. A method for producing radioactive nuclides, 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 the electron beam (2) is spread over an annular area of ​​each converter disk (12), whereby a beam of bremsstrahlung photons is generated for irradiation of a production target (17), the converter target (20) being cooled by a flow of a cooling medium, in particular gaseous helium.

[0077] 48. A method according to Example 47, in which a converter target (20) is constructed 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) such that the focal point of the electron beam (2) is spread over an annular area of ​​the entrance window disk (23).

[0078] The detailed description of the invention continues with reference to the accompanying drawings. [Brief description of the drawings]

[0079] [Figure 1] FIG. 1 shows a schematic diagram of a photonuclear irradiation set-up assembly. [Diagram 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 with respect to the axis of rotation. [Diagram 3] FIG. 1 shows an exemplary illustration of angular beam patterns on a rotating disk. [Figure 4] FIG. 13 shows a comparison of the time structure of an electron beam generated by a linear accelerator (2.4 mA) with that of a roadtron (3.125 mA) with similar beam power. [Diagram 5]For example, FIG. 1 shows the effect of energy deposition on a beryllium (Be) vacuum foil as a function of the beam's full width at half maximum (FWHM). [Figure 6] FIG. 1 illustrates the effect of energy deposition on, for example, a beryllium (Be) vacuum window foil mounted on / within the hollow shaft of a rotary vacuum feedthrough. [Figure 7] FIG. 1 shows a proposed scheme for irradiation of a rotating, e.g., beryllium (Be), vacuum window foil. [Figure 8] FIG. 13 shows the maximum temperature reached depending on the foil thickness and beam FWHM when a beam of 40 MeV electrons with a beam power of 125 kW passes through a rotating vacuum window assembly. [Figure 9] FIG. 1 illustrates the deposition pattern of an oscillating electron beam on a moving surface. [Figure 10] Figure 1 shows a schematic of the distribution of beam pulses on a rotating disk, e.g., a tantalum disk of 1.125 mm thickness. [Figure 11] Figure 1 shows the maximum temperature reached by passage of a beam of 40 MeV electrons and 125 kW beam power through a 1.125 mm thick converter disk rotating at 24,000 rpm and cooled by a fast flow of helium gas. [Figure 12] FIG. 1 shows a schematic diagram of the design of a Tesla turbine / pump type rotating disk converter. [Figure 13] Figure 1 shows the configuration of four partially overlapping disks as a converter target. The left part provides a perspective view. In the right part, a view of the electron beam direction is given. [Figure 14a] 14A-14C show various disk configurations that may be employed in conjunction with FIG. 13. [Figure 14b] 14A-14C show various disk configurations that may be employed in conjunction with FIG. 13. [Figure 15] FIG. 13 shows an example of a slotted disk to avoid distortion due to large thermal loads. [Figure 16]The location of the water-cooled aluminum column, which acts as an exit window and flattening filter to prevent irradiation of the sample target by electrons and low-energy photons, is shown. Additionally, it is shown that multiple production targets can be simultaneously irradiated with the same photon beam. [Figure 17] Table 1 shows the calculated energy deposition of a 40 MeV electron beam with 125 kW beam power in a point source converter assembly. In the calculations, a hypothetical Tantalum (Ta) converter was subdivided into four sections, each 1.125 mm thick, for better cooling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] According to the present invention, the keys to the industrial implementation of photonuclear reactions for medical radionuclide production are the following components: 1.) High power 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 Less and less target material must be available for Mo production or production targets. The target material is mostly valuable isotopically enriched material (i.e. 67 For Cu generation 68 Zn) or harmful highly radioactive materials (i.e. 226 Ra). 3.) A method capable of withstanding high energy and high intensity photon flux while safely and without damaging hazardous and / or radioactive target materials (i.e. 226 A production target design capable of containing Ra). 4.) An automated chemical procedure to extract the desired radionuclide in a quality and quantity suitable for medical use.

[0081] Addendum 1): Several designs of electron accelerators have been developed in the past to generate bremsstrahlung radiation up to 10 MeV, mainly for sterilizing medical devices or curing polymers. Currently, accelerators with beam energies of 30-40 MeV and beam powers of more than 100 kW are commercially available.

[0082] Addendum 2): No high-power point-source converter target capable of converting electron beams above 20 MeV and beam powers above 100 kW into bremsstrahlung has been developed. This has effectively prevented the use of photonuclear reactions for large-scale production of medical radionuclides. The description of such converter targets is the main topic of current applications.

[0083] Addition 3): Current methods can be adapted to the task because the target material can be encapsulated within a relatively thick, high strength, high temperature material.

[0084] Addition 4): 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.

[0085] 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.

[0086] FIG. 1 shows diagrammatically a preferred assembly of a photonuclear irradiation set-up comprising a high power electron beam 2 provided by an electron accelerator 1, a vacuum beam line 3, a fast acting vacuum valve 4 (slammer valve) arranged in the beam line 3, several beam optical elements (5a-c) for focusing or defocusing the beam 2 to different full width at half maximum (FWHM), a beam wobbler including beam deflection units 6 and 7, 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 a means, i.e. inlet and outlet ports 10 for supplying a cooling medium flowing through the housing 9, and the rotating converter target 20 including several (here one) rotating converter disks 12 surrounded by the housing 9. Also shown are the distributed beam spots 14 (traced over time) on the rotating converter disk(s) 12, the rotation axis 13 of the converter disk(s) 12 coupled to a rotary drive 27 with associated control unit 24, the emergence cone 15 of bremsstrahlung photons, the flattening filter and neutron absorber 16, the production target(s) 17 and the bulk high density beam stop 18.

[0087] As will become clear from FIG. 1 and from the detailed description below, a vacuum window holder 8 including a mounted vacuum window disk 23 arranged in 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 arranged in the cavity 19 and generates bremsstrahlung photons 15. A flattening filter 22 and a neutron absorber 16 arranged in the housing 9 serve as an outlet or exit window 22 for a photon cone 15 leaving 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 an airtight manner against the external environment. That is, the entrance window 8 and the flattening filter exit window 22 provide an airtight barrier but are transparent for the electron or photon radiation, respectively. A flow of cooling medium, particularly cooling gas, within cavity 19 provides cooling to converter target 20 by flowing over the interior surfaces of the cavity 19, and also to vacuum window holder 8 including a rotating vacuum window disk 23. This cooling flow enters and leaves cavity 19 by passing through cooling medium inlet and outlet ports 10 located in the housing wall. The housing wall may further be cooled by a flow of a cooling liquid, particularly cooling water, through suitable flow paths.

[0088] The cooling flow through the cavity 19 is part of the cooling circuit 11, which is only diagrammatically shown in FIG. 1. Advantageously, gaseous helium is used as the cooling medium. The pressure of the cooling gas inside the cavity 19 is preferably in the range of atmospheric pressure, in order to keep the pressure difference on the inlet window 8 and on the flattening filter outlet window 22 within manageable limits. However, in the case of a Tesla turbine formed by the converter disk 12, which will be described further below, the cooling gas inlet port is preferably in the range of atmospheric pressure, in order to keep the pressure difference on the inlet window 8 and on the flattening filter outlet window 22 within manageable limits. 5 The cooling gas supply may include a nozzle designed for a discharge pressure of 100 psi (200 psi) at 200 psi (100 psi) and directing the cooling gas in a tangential manner to the outer periphery of the converter disk 12.

[0089] As will be appreciated in more detail below, the axis of rotation 13 of the converter disk 12 is arranged off-center (shifted parallel to) with respect to the axis of the electron beam 2 .

[0090] 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 .

[0091] The unit comprising a housing 9 including cooling gas 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.

[0092] 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. Although it is convenient for these functions to be integrated into a single exit window 22 in the housing 9, in addition to the exit window 22 for high-energy photons, there may be several additional filters of the kind mentioned above, integrated into one assembly or realized as separate components. For example, there may be a simple exit window 22 sealing the housing 9 in an airtight manner against the external 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.

[0093] More specifically, an industrial radionuclide production facility using photonuclear reactions preferably comprises: High power electron accelerator. · 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 allowing focusing or defocusing of the beam to different FWHM, for example in the form of a quadrupole triplet. A beam optical element, preferably called a "beam wobbler", that allows rapid movement of the beam in the x and y directions at high frequencies. Vacuum windows that separate the accelerator and beam line vacuum from the converter target assembly. A housing containing the converter target assembly. · Provisions and connections for cooling gas and / or cooling 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 sync with the beam structure of the beam, the incident beam packet is distributed 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. Neutron filters, 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 an additional (optional) irradiation position for precious stone coloring. A cooling loop, particularly a gas cooling loop preferably including a pump, reservoir, heat exchanger, and filter for cooling the converter target assembly.

[0094] Figure 2 shows the rotating vacuum window assembly diagrammatically. The electron beam 2 is impinging on an off-centered beryllium vacuum window disk 23. The beryllium vacuum window disk is mounted in a ring-like holder 8 attached to a rotating hollow shaft 30 vacuum feedthrough 30. Alternatively, the holder 8 may be an integral part of the hollow shaft 3. On the left side, the rotating vacuum window assembly is connected to the beam transfer line 3. On the right side, there is a cavity 19. The hollow shaft 30 with its magnetic fluid seal 31 and bearings 32 separates the vacuum of the accelerator 1 and the beam transfer line 3 from the cooling gas atmosphere of the housing 9. The hollow shaft is driven by a rotary drive 26 and a corresponding control unit 25 (schematically shown in Figure 1).

[0095] In attached Table 1, the energy deposition of a 40 MeV electron beam with 125 kW beam power is calculated using a beryllium vacuum window and a distributed four-section tantalum (Ta) converter and a water-cooled aluminum planarizing filter to predict the heat load and required cooling capacity of the individual components.

[0096] In the following sections, preferred embodiments and basic concepts of the individual components are described in more detail.

[0097] "1) Synchronization of the rotating vacuum window and converter target with the beam structure" In the presented approach, a fixed beam spot is guided onto a rotating disk (vacuum window or converter target). To distribute the heat load over the disk, the revolution times of these components are synchronized with the beam structure. The beam time structure describes the beam with respect to time, the beam impact time t I , period time t P It can be modeled using the time interval between two pulses, denoted as duty factor D=tI / t P is related to two time intervals and can vary between 0 and 1. The disk rotation is governed by a single parameter, the revolution time t R The revolution speed (in rad / s) can be described by ω=2π / t R The system described in this way is equivalent to a fixed disk and a rotating beam. (The radial component r and the angular components

number

number

number

number

[0098] Therefore, the angle covered by the illuminated beam path is Δ=e k -s k =2πα is given by:

[0099] If the revolution time is selected as a multiple of the impact time, it becomes clear from this formula that the ratio α defines the number of segments on the disk (e.g., if α=1 / 3, then Δ=2π / 3, so the disk is divided into 3 sectors). Moreover, the distance between two consecutive start and end points is given by Δs=s k+1 -s k =2πβ Δe=e k+1 -e k =2πβ It can be written as:

[0100] From these relations it is clear that β=1, 2, 3, .. should be avoided. In these cases the angle between two successive starting points is one or more full revolutions, so that the starting point is always at the same position. This is only acceptable if α=1 and anyway there is only one sector on the disk. Together with the relation β=α / D the above relations can be used to select the revolution time for a given duty factor in order to optimize the illumination pattern. As an example, the illumination pattern is depicted in FIG. 3 for various α and duty factor D=1 / 5.

[0101] More specifically, Figure 3 shows an exemplary illustration of the angular beam patterns on a rotating disk for a duty factor of 1 / 5 and various α. For illustrative purposes, the radius of each successive illumination path is increased in steps. The crosses and dots indicate the start and end points, respectively. The respective sectors for each α are also shown.

[0102] "2) Electron beam accelerator and specifications" An electron accelerator suitable for inducing photonuclear reactions must satisfy several requirements regarding electron beam energy, beam intensity (beam power), beam time structure, and beam 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, a prerequisite for the production of useful radionuclides for medical applications.

[0103] Linear accelerators with electron energies between 35 MeV and over 100 MeV and maximum beam powers between 35 kW and 120 kW are commercially available. Peak current intensities from 200 mA to 300 mA are available with variable repetition rates up to 800 Hz, resulting in average beam currents of up to 4 mA. One pulse length can be up to 16 μs [1a]. The electron beam can be shaped to different full widths at half maximum (FWHM) by the use of beam optical elements. The beam profile can be selected to be non-Gaussian (i.e., flat-top profile).

[0104] Accelerators of type Rhodotron are commercially available with electron energies of 40 MeV and maximum beam powers of 125 kW. 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 chosen to be non-Gaussian (i.e., flat-top profile).

[0105] Compared to linear accelerators, roadtrons are advantageous when operated with point source converter targets. Due to the different beam structure, the beam pulses are much longer and of roughly ten times reduced peak intensity compared to linear accelerators. The beam power can therefore be spread over a larger area, quickly moving the vacuum windows and components of the converter assembly, thus significantly reducing the peak temperatures induced by the passage of the intense electron beam. This situation is illustrated diagrammatically in Figure 4.

[0106] More specifically, Figure 4 shows a comparison of the time structure of the electron beam generated by the linear accelerator with that of the electron beam generated by the rodetron. In this example, the linear accelerator was assumed to generate beam pulses of 15 μs duration and 200 mA peak current with a pulse repetition rate of 800 pps. This results in an average beam current of 2.4 mA with a 1.2% duty cycle. The rodetron is operated at 50 Hz and generates beam pulses of 2.5 ms duration with a peak current of 25 mA. This results in an average beam current of 3.125 mA with a 12.5% ​​duty cycle. Due to the longer pulse duration with lower peak current, the energy deposited in the converter can be distributed along one complete revolution of the converter disk if the converter disk is rotated once in 2.5 ms (i.e., at 24,000 rpm).

[0107] In principle, linear electron accelerators could also be built superconducting, which would allow even longer duty cycles up to 100% and much higher beam currents. The advantages of the long duty cycle of the roadtron mentioned above therefore also apply to superconducting linear accelerators. The present invention of the converter target should also be applicable to superconducting linear accelerators. However, there are currently no commercially available superconducting linear accelerators and only industrial production would reduce the initial investment to a commercially acceptable level. Furthermore, superconducting accelerators require the associated infrastructure for cooling down to about 4.5 K, which to some extent offsets the advantage of the accelerator's lower power consumption.

[0108] "3) High-speed acting valve (slammer valve)" To protect the accelerator and beam line from vacuum window cracking and material transfer into the accelerator cavity(ies), a fast-acting valve is installed, triggered by a pressure sensor placed in front of the vacuum window and downstream of the beam line. In case of vacuum window cracking, the fast-acting valve physically closes the cross-sectional area of ​​the beam line within milliseconds before the front of the penetrating shock wave reaches the accelerator.

[0109] "4) Vacuum window" The electron beam from the accelerator must pass through a vacuum window that separates the accelerator vacuum from the converter cooling circuit. This window must withstand the electron beam intensity while its mechanical stability remains intact. Therefore, this window must be made of a material with a high melting point, good mechanical strength and low atomic number to allow the passage of the electron beam with a small energy drop. Furthermore, the vacuum window material should be relatively chemically inert and should not react with the components or trace elements of the cooling circuit. A suitable material for the vacuum window is a foil made from beryllium. 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.

[0110] Vacuum windows made from beryllium foils with thicknesses between 20 and 100 μm were considered. At this thickness, the number of electrons greater than 1 MeV lost by passing through the Be foil is less than 2%. The energy deposited in the foil depends on the foil thickness, but does not exceed 80 watts for a 100 μm thick window. The temperature variation in the center of the beam spot depends strongly on the FWHM of the beam. For a beam with FWHM of 1 mm passing through a thin Be window of 20 μm, temperature variations of about 250 °C are observed with a time constant of 50 Hz, resulting in significant mechanical stress of the foil. Since the deposited energy scales almost linearly with the vacuum window thickness, a beam width of 1 mm FWHM and a thickness of 100 μm leads to cracking of the vacuum window. As shown in Figure 5, broadening the beam profile can significantly reduce temperature variations, but at the expense of broadening the angle of the cone of high-energy photons emitted by the converter target, resulting in a lower flux intensity at the irradiation site of the production target.

[0111] More specifically, Figure 5 shows the effect of energy deposition on a Be vacuum foil as a function of the beam's FWHM, with FWHM values ​​of 1 mm, 3 mm, and 5 mm shown.

[0112] To further reduce the temperature variations, the entrance vacuum window is made rotatable (see Fig. 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 with a magnetic fluid seal. A commercially available 4 cm rotary vacuum feedthrough can be rotated at a maximum speed of about 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 an impact zone of 3 cm diameter.

[0113] More specifically, Figure 6 shows a schematic of a 4 cm diameter Be foil mounted on the hollow shaft of a rotary vacuum feedthrough. One side is cooled by flowing He gas.

[0114] The rotation speed was chosen as 2,666 rpm. In this way, 9 segments are formed, each of which is irradiated for 2.5 ms, followed by nine 20 ms cooling periods, and then the same segment is irradiated again. A schematic is shown in Figure 7. With the proposed set-up, the energy deposited on the foil is distributed over a larger area of ​​the foil, and the next beam pulse irradiates areas that have taken significantly more time to cool down since the last irradiation.

[0115] More specifically, Figure 7 shows the proposed scheme of irradiation of a rotating Be foil vacuum window. The foil is rotating clockwise. With the proposed scheme of irradiation at 50 Hz and a beam configuration of 12.5% ​​duty cycle, the cooling period of the irradiated part is maximized.

[0116] The proposed set-up allows the use of thicker Be foils, which are therefore less susceptible to cracking of the vacuum window. The maximum temperature reached depending on the Be foil thickness and the FWHM of the beam is displayed in Fig. 8. As can be seen, the maximum temperature is significantly reduced. For a window thickness of 100 μm and a FWHM of the beam of 2 mm or more, the maximum temperature reached is less than 130 °C.

[0117] More specifically, Figure 8 shows the maximum temperature reached depending on the foil thickness and beam FWHM when a beam of 40 MeV electrons with a beam power of 125 kW passes through a rotating vacuum window assembly. The beam is deposited in a ring with a diameter of 3 cm and the assembly is rotating at a speed of 2666 rpm.

[0118] In practical experience, it is difficult to guarantee a FWHM greater than 2 mm FWHM at any time. A finer focusing of the beam has the potential to destroy the vacuum window, which may result in an unscheduled shutdown of the facility. It is therefore advantageous to install a beam wobbler system. In its simplest configuration, it consists of two sets of parallel plates (beam deflectors) to which an electric field is applied. One set of parallel plates directs the beam in the x direction, the other directs it in the y direction. By applying a sinusoidally varying voltage to both sets of plates, the beam can be brought into a circular motion. This results in a more rectangular beam profile and a deposition pattern of the beam on a moving trajectory, as depicted in Figure 9. In this way, accidental focusing of the beam on the vacuum window or on the converter target can be avoided, at the expense of a slightly larger widening of the angle of the emerging bremsstrahlung cone. The circular motion of the beam can also be achieved magnetically by using the stator of an electric motor. More complex patterns, known as Lissajous figures, are possible depending on the frequency of the voltage applied to the deflection plates.

[0119] "5) Electronics, housing, and cooling for photon converters" The electron beam then impinges on 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 of high density in order to effectively convert the electron beam into bremsstrahlung. The high atomic number and high density contribute to a relatively ideal point source generation of bremsstrahlung. For reasons of maintenance and radioactive waste management, the converter material should be only slightly activated by the electron beam. Furthermore, the converter material should be relatively chemically inert and should not react with the components or trace components 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.

[0120] The interaction of electrons with the converter material can be described by a number of physical processes, but is rather complex. For the production of radionuclides in photonuclear reactions, bremsstrahlung photons with energies above about 8 MeV are important. However, to take into account 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 mainly emitted in the forward direction (beam direction) in the form of a cone with a certain divergence angle.

[0121] The vacuum window and converter target materials must be cooled due to the energy deposited by the intense electron beam. Blackbody radiation is overwhelmingly insufficient to dissipate the deposited energy. Therefore, the vacuum window and converter must be cooled by a liquid or gas. In our discussion, cooling by flowing helium gas is suggested. Helium has the advantage of being a material with high viscosity and low atomic number that cannot be activated or degraded by bremsstrahlung photons.

[0122] 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 needs 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. Additionally, natural tantalum is rich in two isotopes, i.e. tantalum with a natural abundance of 99.98799%. 181 Ta, with a natural abundance of 0.01201% 180m It consists only of Ta. 181 For the (γ,n) or (γ,2n) reaction on Ta, 180 Ta itself, or stable with a half-life of 665 days 179 Become Hf 179The latter decays by electron capture without the emission of gamma rays. It has a half-life of 8.15 h. 180 The formation of Ta requires further investigation, but its decay could lead to a stable 180 W or stable 180 In the (γ,pxn) reaction on Ta, the stable Hf isotope is formed. 182 The formation of Ta is expected to contribute only to minor activation of the Ta converter material.

[0123] Moreover, tungsten can be considered a good converter material due to its high melting point of 3422°C. Furthermore, natural tungsten contains five isotopes, i.e., 0.12% natural abundance. 180 W, with a natural abundance of 26.50% 182 W, with a natural abundance of 14.31% 183 W, with a natural abundance of 30.64% 184 W, with a natural abundance of 28.43% 186 It consists of W. 180 In the (γ,n) or (γ,2n) reaction with W, it decays to a stable γ-atom with a half-life of 665 d, respectively. 179 Become Hf 179 Ta, or collapse 178 Relatively short-lived 178 W(T 1 / 2 =22d) or 182 W and 183 The (γ,n) or (γ,2n) reaction with W has a half-life of 121.2d. 181 W is formed, which decays by electron capture under the radiation of X-rays and very low energy gamma rays to form the stable 181 Become Ta. 186 The (γ,n) reaction with W has a half-life of 75.1 d. 185 W is formed, which decays with low branching ratios by beta-minus radiation (0.4 MeV) and 125 keV gamma radiation to form stable 185 Become Re. 183 W and 184In the (γ,p) or (γ,pn) reaction with W, the half-life is 114.43d. 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.

[0124] 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.

[0125] To distribute an energy deposition of about 45 kW in a 4.5 mm thick Ta converter slab (Table 1), the converter target is split into multiple disks, specifically, four disks, for example, 1.125 mm thick and about 18 cm in diameter. The energy of a 2.5 ms long beam pulse is distributed around the circumference of a rotating disk, assuming a diameter of 15 cm. As discussed above, the rotation speed of the disk is preferably synchronized with the time structure of the beam (specifically, at a specific rotation per beam packet) resulting in a rotation speed of 24,000 rpm (see Figure 10).

[0126] More specifically, Figure 10 shows a schematic of the distribution of the beam pulse on a rotating tantalum disk of 1.125 mm thickness.

[0127] The number of discs can be increased while the overall thickness is adjusted to an optimum value between 4.5mm and 5mm.

[0128] The maximum temperature reached depends on the FWHM of the electron beam. In Fig. 11 the maximum temperature reached for a 1.125 mm thick Ta disk is displayed depending on the beam FWHM. The energy deposited in the actual converter amounts to about 45 kW. To remove this heat, a helium gas flow of about 250 L / s is required at standard temperature and pressure (STP), assuming that the helium gas exit temperature is 200°C higher than the entrance temperature. This rather high He flow rate can be achieved with a commercially available medium-sized pump. As can be seen in Fig. 11, despite the high speed rotation of the converter disk, the temperature approaches the melting point of Ta for a 1 mm FWHM beam. However, for beam FWHMs larger than 2 mm, manageable temperatures below 1500°C occur. It should be noted that for a stationary target the temperature should be in the range of 20,000 to 40,000°C for beam FWHMs of 5 or 2 mm, respectively.

[0129] More specifically, Figure 11 shows the maximum temperature reached by a beam of 40 MeV electrons and 125 kW beam power passing through a 1.125 mm thick converter disk rotating at 24,000 rpm (energy deposited in a 15 cm diameter ring) and cooled by rapid flow of helium gas. Note that at a FWHM of 2 mm or greater, the maximum temperature reaches an experimentally manageable temperature of less than 1500 °C.

[0130] The rotating converter disk and the associated flow of He cooling gas can be configured in one of three different particularly advantageous configurations.

[0131] Configuration 1 & 2 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 is preferably a multiple (or submultiple) of the electron beam pulse duration (e.g., 24,000 rpm for a 2.5 ms pulse duration). 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. An orifice concentric with the shaft is envisioned to facilitate axial gas flow along the shaft. The housing incorporates openings to allow gas circulation to and from the outer edges of the disks. This configuration describes an adhesion type turbine / pump, also called a Tesla turbine / pump, which was originally described in US Pat. No. 5,393,326, which is incorporated herein by reference.

[0132] The gas flow between the disks was spiralled (swirled) due to the interaction of the gas with its adhesion to the disks and the internal viscosity. In the turbine configuration, the pressure difference between the inlet and the outlet drives the rotation of the disks by wall friction, where the gas flows from the periphery towards the centre of the disk. Due to the induced high speed rotation, the contact time of the gas with the disk surface is increased and the heat transfer to the cooling gas is optimised. In the pump configuration, the shaft is externally driven and the gas flow is reversed to flow from the shaft towards the outer edge of the disk.

[0133] For both flow patterns, the predominantly radial flow of the cooling gas allows 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 will be comparable to the figures presented above with approximately 45 kW of power absorbed in the converter material (see Table 1), but the load per disk can be reduced. Figure 12 shows a diagram of the design of the turbine (left) and pump (right) configurations (housings not shown).

[0134] More specifically, Figure 12 shows a diagram of the Tesla converter design. On the left, the entire disk assembly is shown in a turbine configuration including a shaft and multiple disks, where 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 cooling gas flow pattern over a single disk is drawn for the converter in pump configuration. The direction of the flow pattern is reversed in the turbine configuration.

[0135] Configuration 3 In this configuration, the disks are arranged in the form of partially overlapping circles, as displayed in Figure 13. In this way, part of the energy can be dissipated by blackbody radiation to the walls of the container vessel, and exposure of a large area to the rapidly flowing cooling gas is achieved. The disks are externally driven and all rotate in the same direction, either clockwise or counterclockwise, preferably at a speed that is a multiple (or submultiple) of the electron beam pulse duration, as discussed above (e.g., 24,000 rpm with a pulse duration of 2.5 ms).

[0136] More specifically, Figure 13 shows a configuration of four (e.g., Ta) disks as converter targets. The disks are 1.125 mm thick and spaced at a distance of 1 mm between the disks (left). In the right part, a view into the electron beam direction is given. The disks are rotating at 24,000 rpm and are driven externally. A flow of He is used to cool the configuration.

[0137] In principle the number of disks can also be reduced as illustrated in Figure 14a.

[0138] Figure 14b shows a converter disc configuration which allows the disc to be mounted on a shaft containing two bearings.

[0139] To prevent distortion of the disks due to thermal expansion, slotted disks can be used when used in cut-off wheels or brake rotor disks, as shown for example in Figure 15. If several disks are employed, as shown in Figure 13, the disks can be arranged in a staggered pattern (no overlapping slots) to ensure total absorption of the electron beam.

[0140] "6) Flattening filter and neutron absorber" The exit window of the converter-target assembly can be made of beryllium foil or constructed as a flattening filter to protect the target from irradiation by electrons, x-rays and low-energy gamma rays. The flattening filter is made, for example, from a rectangular aluminum profile with a wall thickness of 1 mm (see Fig. 16). The inside of the profile realizes a channel, for example 3 mm thick, which is flushed with a cooling fluid, in particular with cooling water. The task of this unit is to filter out and significantly reduce the flux of low-energy photons that do not contribute to the photonuclear reaction. The reduction in the number of electrons compared to the number of source electrons due to the introduction of the flattening filter reaches 20.8%, with the maximum reduction in the energy range from 0 to 8 MeV being 11.2%.

[0141] Irradiation of the converter material with high energy electrons also generates photoneutrons in the (γ,xn) photonuclear reaction. These neutrons can induce unwanted neutron capture reactions in the production target, resulting in unwanted by-products and reducing the radionuclide purity of the product. One such example is 226 Long lifetimes in the (n,γ) reaction on Ra. 227 Ac(T 1 / 2 =21.773a). 227 Ac by-products pose significant waste and radiation protection problems and 225 Depending on its activity percentage compared to Ac, it may destabilize the product. As neutron absorbers, different materials such as gadolinium, cadmium, or boron, or combinations thereof, can be utilized.

[0142] More specifically, Figure 16 shows the location of a water-cooled aluminum column that acts as an exit window and flattening filter to prevent irradiation of the sample target by electrons and low-energy photons.

[0143] Figure 16 shows a converter target of the stacked disk type known from Figure 13, but this is only an example. Of course, the cooling arrangements described above and the beam stop of Figure 16 can also be combined with other converter types.

[0144] "7) Generation target(s)" 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, without limitation, 48 Ca, 48 Ti, 68 Zn, 100 Mo, 112 Sn, or 150The target (highly isotopically enriched material such as Nd) should 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 The generation of Mo in the target material 100 "Carriers 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 concentrated 100 This can only be achieved by irradiation of Mo, provided that the photons emerge from a point such as the converter source. Photons with energies of 8 MeV and above are highly penetrating, so that 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 energies have the advantage that target materials that are difficult to handle because of their radioactivity, toxicity or chemical reactivity can be safely contained in materials suitable for irradiation. Thus, cracks in the target material that get into the cooling water circuit can be avoided. 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 48A bulk target of Ti follows, although chemical separation and regeneration procedures already exist when dealing with large amounts of target material. Preferably, provisions are made to remotely load, remove, and transport the target to the processing hot cell.

[0145] "8) Lumped 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 table 1, the energy deposited in the beam stop amounts to about 68 kW. For shielding, one can imagine a vertical configuration of the electron beam, converter and generation target, with the ground as additional shielding around the solid beam stop. In another case, additional shielding (i.e. concrete) must be put in place to reduce the gamma radiation dose to acceptable levels.

[0146] Inside the bulk beam stop, it is possible to foresee a way to irradiate artificial precious stones. High-energy gamma radiation induces defects in the lattice of artificially grown precious stones, which act as color centers, allowing the permanent coloring of artificially grown precious stones, such as topaz.

[0147] "9) Cooling circuit" Helium gas has preferably been chosen as the cooling medium due to its low atomic number and density, its chemical inertness, and reasonable heat capacity. Furthermore, He is not reactive with high energy Bremsstrahlung photons. Assuming a temperature increase of 200°C, about 250 L / s of He at STP would be required to remove the energy deposited in the converter target assembly. It is foreseen that the He gas enters the converter assembly at room temperature. The He gas is preferably circulated in a gas loop. Thus, the cooling circuit preferably comprises 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 He gas. The pressure in the He 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. Chillers capable of removing heat on the order of 100 kW or more are available for building air conditioning units.

[0148] Calculated yields of radionuclides (examples): Using the point source high power converter target assembly as described above and the production target configuration as shown in schematic Figure 16, assuming an electron energy of 40 MeV and a beam power of 125 kW, the following yields can be obtained:

[0149] 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 at position 1 of the target assembly, 225 The production of Ra / day was calculated 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, 225The first batch of Ac can be separated from the irradiated target. Soon after, with an optimal waiting time of about 17 days, it will decay to 14.9 d half-life. 225 The fall of Ra 225 Thanks to Ac's internal growth, the so-called second and third opportunities 225 Ac can be separated from the irradiated target. Assuming such a production method and a dose of 10 MBq per patient, one 226 Approximately 500 patient doses can be generated per day from the Ra target.

[0150] 100 From Mo 99 Mo generation 1g / cm 2 With a target thickness of 1000 nm and a target diameter of 2 cm at position 1 of the target assembly, approximately 650 GBq of irradiation was achieved. 99 Mo / day production was calculated, which corresponds to approximately 17.5 Ci / day / target. 1 g / cm 2 , the target thickness is still relatively thin.

[0151] 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 up to 125 kW, allowing routine radionuclide production using a roadtron-type electron accelerator.

[0152] 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] [Explanation of symbols]

[0153] 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) 6, 7 Beam deflection unit (vertical and horizontal steering magnets) 8 Inlet window holder for vacuum window 9. Housing 10 Coolant ports (inlet and outlet ports) 11 Cooling loop (cooling circuit) 12 Converter Disks 13 Rotation axis 14 Projected focal beam spot (trace in time) 15 Bremsstrahlung photon cone (photon field) 16 Neutron absorber 17 Generation Target 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 disk rotary drive 30 Hollow Shaft 31 Magnetic fluid seal 32 Bearing 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); a converter target assembly (21) including a converter target (20) for converting said 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) has a sealed housing (9), the housing (9) comprising: - surrounding a cavity (19) that holds said 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 said cavity (19), thereby cooling said converter target (20) and said window disk (23); - said converter target (20) comprises several rotating converter discs (12); the electron beams (2) are offset relative to their respective converter disks (12); The installation, wherein each converter disk (12) is designed to rotate during operation of the installation, thereby, in time, spreading the focus of the electron beam (2) over 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) or a continuous wave electron beam (2), the pulsed electron beam (2) having an impact time 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 time structure of the electron beam pulses.

4. 4. The equipment of claim 3, wherein the area on each converter disk (12) exposed to a single beam pulse describes a complete ring (14) or a sector thereof, and the ratio of the revolution time of the converter disk (12) to the beam pulse time is preferably selected so that all sectors are uniformly irradiated over multiple irradiation cycles.

5. 3. The installation according to claim 1 or 2, wherein the rotation speed of each converter disc (12) is set within a range of several thousand to several tens of thousands of revolutions per minute.

6. 3. The installation according to claim 1 or 2, 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 eventually spreading the focus of the electron beam (2) over an annular area of ​​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, are sealed to the beam transfer line (3) by a magnetic fluid seal (31).

9. 7. The installation according to claim 6, 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 pulses.

10. 10. The installation according to claim 9, wherein the area on the window disk (23) exposed to a single beam pulse describes a complete ring or a sector thereof, and the ratio of the revolution time of the window disk (23) to the beam pulse time is preferably selected so that all sectors are uniformly irradiated over multiple irradiation cycles.

11. 3. The installation according to claim 1 or 2, wherein the rotation speed of the window disc (23) is set within the range of several hundred to several thousand revolutions per minute.

12. 3. The installation according to claim 1 or 2, wherein the beam transfer line (3) comprises optical elements (5a-c) that enable focusing or defocusing of the electron beam (2) to different FWHMs, with a FWHM of at least 2 mm being set.

13. 3. The installation according to claim 1 or 2, wherein the converter target (20) comprises a plurality of preferably circular converter discs (12), in particular four converter discs (12).

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

15. 14. The installation according to claim 13, wherein the converter disks (12) are arranged on the parallel shafts so as to overlap each other when viewed in the direction of the parallel shafts, and each shaft (13) is aligned parallel to the direction of the electron beam (2).

16. 3. The installation according to claim 1 or 2, wherein each converter disk(s) (12) is / are coupled to a rotary drive (27).

17. 3. The installation according to claim 1 or 2, wherein the converter disc (12) is configured to form a Tesla pump.

18. 3. The installation according to claim 1 or 2, wherein the converter disc (12) is designed to be driven by the cooling flow.

19. 19. The installation of claim 18, wherein the converter disc (12) is configured to form a Tesla turbine.

20. 3. The installation according to claim 1 or 2, wherein the cooling medium is a cooling gas.

21. 3. An installation according to claim 1 or 2, wherein, apart from any optional oscillations with amplitudes in the millimetre range, the region of occurrence of the emerging bremsstrahlung photons (15) is fixed in space.

22. A converter target assembly (21) for an installation according to claim 1 or 2, comprising a sealed housing (9), said housing (9) comprising: - surrounding a cavity (19) that holds said 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 said cavity (19), thereby cooling said converter target (20) and said inlet window holder (8) including its attached inlet window disk (23); The converter target (20) comprises a converter target assembly (21) having several rotating converter disks (12), each of which is designed to rotate during operation of the equipment, thereby eventually spreading the focus of the incident electron beam (2) over an annular area of ​​the converter disk (12).

23. 23. A converter target assembly (21) as described in claim 22, wherein the entrance window holder (8) has a rotating window disk (23) that is designed to rotate during operation of the equipment, thereby eventually spreading the focus of the incident electron beam (2) over an annular area of ​​the window disk (23).

24. 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.

25. 25. The method according to claim 24, wherein the converter target (20) is arranged inside a housing (9) and the electron beam (2) is guided through a rotating entrance window holder (8) including an entrance window disk (23) mounted on the housing (9) so that the focal point of the electron beam (2) is spread over an annular area of ​​the entrance window disk (23).

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