A system for generating radioactive isotopes by bremsstrahlung with a curved converter.

Abstract

To provide a system for production of radioisotopes by bremsstrahlung comprising a curved converter.SOLUTION: There is provided a system for converting an electron beam into photons, comprising: an electron accelerator 1 configured to generate an electron beam 10 of accelerated electrons along an irradiation axis Z; a scanning unit 2; a focusing unit 3 for forming a focused beam 10f converging towards a first focusing point; a conversion unit 4 arranged between the focusing unit 3 and the first focusing point and comprising bremsstrahlung converters 4.1 to 4.n configured to convert the focused beam into a photon beam 11x; and a target holder 5h configured for holding a target 5, wherein the bremsstrahlung converters are curved such that the focused beam intersects each of the bremsstrahlung converters with an intersecting angle α comprised between 65° and 115° at all points, preferably between 75° and 105° at all points.SELECTED DRAWING: Figure 1a-1c

Description

[Technical Field]

[0001] The present invention relates to an apparatus for producing radioactive isotopes by irradiating a target with X-rays formed by bremsstrahlung when a converter is directed towards a high-energy electron beam. More specifically, the present invention relates to a particular shape of a converter that reduces the heat generated by the electron beam and allows the use of a conventional cooling system to maintain the converter temperature within an acceptable boundary. [Background technology]

[0002] Radioactive isotopes can be produced by various reactions using charged particles or photonuclear reactions (e.g., X-rays). For example, 225 Ac is 226 Formed by photonuclear reactions caused by X-ray irradiation of the Ra target. 225 It can be prepared by the decay of Ra. To form the desired isotope, the energy of the X-rays, which directly depends on the energy of the electron beam, must be precisely controlled. For example, 226 By irradiating the Ra target, depending on the energy of the light irradiation, 223 Ra, 224 Ra, and 225 Ra can be obtained. Other examples of radioisotopes commonly used in medical applications include 99mTc.

[0003] X-rays can be generated by irradiating a converter with a high-energy electron beam. The converter consists of a source and target of the high-energy electron beam, including an electron accelerator such as a rhodetron or linear accelerator (in this example, 226It is positioned between Ra). The converter is formed by a foil of a high-Z metal such as Ti or Ta. As the converter is irradiated by the electron beam, the electron beam is slowed down, and the emitted energy is converted into X-ray radiation, which reaches the target to form the desired radioactive isotope. This mechanism is called "bremsstrahlung".

[0004] In bremsstrahlung, only a portion of the electron beam's energy is converted, with the remainder being converted into heat. Therefore, thermal degradation of the converter is a serious problem. For this reason, the converter must be cooled. Conventional coolers use gases such as helium or liquids such as water.

[0005] To improve converter cooling and / or to enable a broader geometric spread of the resulting photon beam from the converter, (Patent Document 1) proposes scanning the electron beam across the scanning area of ​​the converter by using a magnetic scanning coil. (Patent Document 2) combines the scanning of the electron beam with the parallel motion of a target synchronized with the scanning of the electron beam, so that the target is continuously exposed to the full intensity of the bremsstrahlung radiation produced by the converter.

[0006] (Patent Document 3) describes a focusing lens used to collimate or focus an electron beam. Collimation of an electron beam is useful because it increases the divergence of photons produced by a diverging electron beam. Conversely, this would require a larger target to collect the photons. Focusing lenses can be formed from magnets and may be multipole lenses such as quadrupole, sextupole, or octupole lenses. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Patent Application Publication No. 1999052587 [Patent Document 2] U.S. Patent Application Publication No. 20120025105 [Patent Document 3] International Patent Application Publication No. 2017076961 [Patent Document 4] International Patent Application Publication No. 2012022491

[0008] Despite the improvements described above, adequately cooling the converter with conventional cooling systems to prevent premature thermal degradation remains a problem. The present invention solves the dual problem of preventing premature thermal degradation of the converter using conventional cooling means while simultaneously maintaining a focused high-intensity electron beam and, therefore, highly focused X-ray emission. The solution proposed by the present invention to achieve these dual objectives will be described below. [Overview of the Initiative]

[0009] The present invention is defined in the appended independent claims. Preferred embodiments are defined in the dependent claims. More specifically, the present invention relates to a system for the production of radioactive isotopes, which is... • An electron accelerator configured to generate an electron beam of electrons accelerated along the irradiation axis (Z), • A scanning unit configured to deflect an electron beam along a predefined scanning pattern in order to form a scanning beam, A focusing unit having one or more magnets configured to focus a scanning beam onto a first irradiation plane (X,Z) toward a first focusing point (Fx) located on the irradiation axis (Z), wherein the first irradiation plane (X,Z) is defined by the irradiation axis (Z) and the first transverse axis (X), and X⊥Z, and the focusing unit... A conversion unit having one or more bremsstrahlung converters (4.1-4.n) positioned between a focusing unit (3) and a first focusing point (Fx), configured to convert a focused beam into a photon beam, ·A converter cooling system configured to cool one or more braking radiation converters, ·A target holder configured to hold a target, and has.

[0010] The electron accelerator, the scanning unit, the focusing unit, the conversion unit, and the target holder are all aligned along the irradiation axis (Z) and arranged downstream of each other in this order, where "downstream" is defined in relation to the electron beam direction. This system is distinguished from prior art systems in that one or more braking radiation converters are curved such that the focused beam intersects each of the one or more braking radiation converters at an intersection angle (α) that is 65° - 115° at all points, preferably 75° - 105° at all points.

[0011] In the first embodiment, the scanning unit is configured to deflect the electron beam along a predefined scanning pattern extending along a first transverse axis (X) and a second transverse axis (Y), where X⊥Y⊥Z. The focusing unit is also configured to focus the scanning beam onto a second irradiation plane (Y, Z) towards a second focusing point (Fy) arranged on the irradiation axis (Z). The second focusing point (Fy) can be the same as or different from the first focusing point (Fx). One or more braking radiation converters have the shape of an oval cap, preferably a spherical cap, defined by a first curved cross-section in the first irradiation plane (X, Z) and a second curved cross-section in the second irradiation plane (Y, Z).

[0012] Each of the one or more bremsstrahlung converters preferably has a first curved cross section in a first irradiation plane (X,Z) defined by a substantial arc of radius (d1-dn) centered on a first focal point (Fx). “Substantial arc” is defined herein as a curved segment having a radius of curvature that varies by no more than 10% over the length of the curved cross section. Alternatively, or in addition to this, each of the one or more bremsstrahlung converters preferably has a second curved cross section in a second irradiation plane (Y,Z) defined by a substantial arc of radius (d1-dn) centered on a second focal point (Fy). The second focal point (Fy) is preferably identical to the first focal point (Fx) (i.e., Fx = Fy).

[0013] In the second embodiment, the scanning unit is configured to deflect the electron beam along a predefined scanning pattern extending only along a first transverse axis (X). One or more bremsstrahlung converters have the shape of a cylindrical section defined by a curved cross section in a first transverse plane (X,Z) and a generatrix extending along a second transverse axis (Y), where X⊥Y⊥Z. Each of the one or more bremsstrahlung converters has a first curved cross section in a first irradiation plane (X,Z) defined by a substantial circular arc of radius (d1-dn) centered on a first focusing point (Fx).

[0014] The focusing unit can be configured to form a focused beam having a focusing half-angle (β) formed at a first focusing point (Fx) with respect to the irradiation axis (Z) on a first irradiation plane (X,Z), which includes 20 to 55°, preferably 30 to 45°.

[0015] One or more bremsstrahlung converters can be manufactured from tantalum (Ta) or tungsten (W) or titanium (Ti). Each of the one or more bremsstrahlung converters preferably has a thickness (L90) measured along a radius of curvature of 3 mm or less, and preferably the thickness (L90) includes 0.2 to 2.5 mm, more preferably 0.5 to 1.5 mm. The nth bremsstrahlung converter disposed closest to the target holder preferably has a greater thickness (L90) than the first bremsstrahlung converter disposed closest to the focusing unit.

[0016] The conversion unit can include 1 to n bremsstrahlung converters separated from each other by cooling channels, where n includes 2 to 8, preferably 3 to 5. The converter cooling system can have a forced cooling flow of gas or liquid through the channels.

[0017] The present invention also relates to a process for generating radioisotopes by X-ray irradiation of a target, which · comprises providing a system as defined above, · loading a target onto a target holder, · scanning and focusing an accelerated electron beam onto a conversion unit to generate X-rays, · irradiating the target with the X-rays thus generated, and has.

[0018] The target can be 225 for generating 226 Ra, 99m for forming 100 Mo, 187 for generating 186 W, 131 for forming 134 Xe, or 67 for generating 68 Zn and can be selected from one of them.

[0019] For a full understanding of the characteristics of the present invention, please refer to the detailed description below, which is provided in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0020] [Figure 1a] Figure 1(a) shows a side view of the system according to the present invention. [Figure 1b] Figure 1(b) shows a perspective view of a first embodiment of the system according to the present invention. [Figure 1c] Figure 1(c) shows a perspective view of a second embodiment of the system according to the present invention. [Figure 2] Figure 2 shows a diagram of the scanning and focusing unit according to the present invention. [Figure 3] Figure 3 shows an example of a conversion unit according to the present invention. [Figure 4a] Figure 4(a) shows the maximum distance (Lα) that the electron beam traverses across a straight sheet of a conventional bremsstrahlung converter, where α = β + 90°. [Figure 4b] Figure 4(b) shows the maximum distance (Lα) traversed by the electron beam across the curved sheet of the bremsstrahlung converter according to the present invention, where 65° ≤ α ≤ 115°. [Figure 4c] Figure 4(c) shows the maximum distance (L90) traversed by the electron beam across the curved sheet of a bremsstrahlung converter according to a preferred embodiment of the present invention, where α = 90°. [Figure 4d] Figure 4(d) plots the normalized maximum distance (Lα / L90) traversed by the electron beam across the curved sheet of the bremsstrahlung converter according to the present invention as a function of angle α, where the minimum value of Lα is L90 at α=90°. [Figure 5a] Figure 5(a) shows the height (hi) representing the scanning area of ​​a conventional straight bremsstrahlung converter traversed by the scanning beam. [Figure 5b]Figure 5(b) shows the height (ci) representing the scanning area of ​​the curved bremsstrahlung converter according to the present invention, which is traversed by the scanning beam. [Figure 5c] Figure 5(c) compares the height (hi, ci) of the bremsstrahlung converter traversed by the scanning beam using the conventional technology with that of the present invention. [Figure 5d] Figure 5(d) plots the height ratio (c1 / h1) of the bremsstrahlung converter traversed by the scanning beam as a function of the focusing half-angle (β). [Modes for carrying out the invention]

[0021] The present invention relates to a system for generating radioactive isotopes by converting an electron beam into a photon beam and thereby irradiating a target (5). The system has an electron accelerator (1) configured to generate an electron beam (10) of electrons accelerated along the irradiation axis (Z). A scanning unit (2) is inserted downstream of the electron accelerator along the irradiation axis (Z). The scanning unit (2) is configured to deflect the electron beam (10) along a predetermined scanning pattern to form a scanning beam (10s). A focusing unit (3) is inserted downstream of the scanning unit along the irradiation axis (Z). The focusing unit has one or more magnets (3m) configured to focus a scanning beam (10s) onto a first irradiation plane (X,Z) toward a first focusing point (Fx) located on the irradiation axis (Z) in order to form a focused beam (10f), wherein the first irradiation plane (X,Z) is defined by the irradiation axis (Z) and the first transverse axis (X), where X⊥Z.

[0022] The conversion unit (4) is positioned between the focusing unit (3) and the first focusing point (Fx). The conversion unit has one or more bremsstrahlung converters (4.1-4.n) configured to convert the focused beam (10f) into a photon beam (11x). The conversion unit is equipped with a converter cooling system (4c) configured to cool one or more bremsstrahlung converters (4.1-4.n).

[0023] The target holder (5h) is configured to hold the target (5) in an exposed state at the first focusing point (Fx). The target holder is equipped with a target cooling unit (5c) configured to cool the target (5) while it is held within the target holder (5h).

[0024] The electron accelerator (1), scanning unit (2), focusing unit (3), conversion unit (4), and target holder (5h) are all aligned along the irradiation axis (Z) and are positioned downstream of each other in this order, with "downstream" defined in relation to the electron beam direction.

[0025] The gist of the present invention is that one or more bremsstrahlung converters (4.1-4.n) are curved such that a focused beam (10f) intersects each of them at an intersection angle (α) including 65° to 115° at all points, preferably 75° to 105° at all points, and more preferably the intersection angle (α) is equal to 90° ± 5°.

[0026] Electron accelerator (1) Electron accelerators are well known in the art. The present invention is not limited to any particular type of electron accelerator, as long as it has the ability to generate an electron beam (10) with an energy of 10 to 40 MeV, preferably 15 to 30 MeV, preferably 20 to 25 MeV. The diameter of the electron beam (10) may be less than 10 mm. The electron accelerator may be, for example, a linear particle accelerator (e.g., a linac) or a petal-shaped accelerator (e.g., a rhodtron).

[0027] Scanning unit (2) Scanning units are well known in the art. The present invention is not limited to any particular type of scanning unit, as long as it has the ability to scan an electron beam (10) along a predefined scanning pattern to form a scanning beam (10s). When directed onto a bremsstrahlung converter, only a portion of the electron beam's energy is converted into X-ray energy. The remainder is dissipated as heat. Scanning the electron beam over the converter results in a flat beam distribution across the entire surface of the converter, reducing beam power concentration and heating within small scanning areas of the converter.

[0028] The scanning unit (2) may be equipped with a scanning magnetic coil (2m) in the lateral direction of the electron beam (10). The scanning magnetic coil may be configured to scan the electron beam linearly along a first transverse direction (X), as shown in Figure 1(c). Alternatively, the scanning magnetic coil may be configured to scan the electron beam over a scanning area along first and second transverse directions (X, Y), as shown in Figure 1(b).

[0029] In the first embodiment, the scanning unit (2) is configured to deflect the electron beam (10) along a predefined scanning pattern that extends only along the first transverse axis (X). Alternatively, in the second embodiment, the scanning unit (2) is configured to deflect the electron beam (10) along a predefined scanning pattern that extends along the first transverse axis (X) and the second transverse axis (Y), where X⊥Y⊥Z.

[0030] As described above, scanning the electron beam in the first transverse direction and optionally in the second transverse direction on the converter promotes the cooling of the converter. However, this results in a broader geometric spread of the photon beam thus formed. In some cases, this can be an advantage when a large target is available. However, if the target material is not sufficient, 226When small-sized targets such as Ra are used, the broad geometric spread of X-rays can be undesirable. For this reason, in this art, it has been proposed to use a focusing unit to focus the scanning beam (10s) onto the converter via a focusing magnetic coil (3m).

[0031] Focusing unit (3) Therefore, the scanning beam (10s) cannot be used efficiently for smaller targets because the photon beam (11x) formed by the interaction of the scanning electron beam with the conversion unit (4) also spreads out. For smaller targets, refocusing of the scanning beam (10s) or the photon beam (11x) is required. Focusing of the photon beam (11x) is described, for example, in (Patent Document 4). In the present invention, the system has a focusing unit (3) positioned upstream of the conversion unit (4) to focus the scanning beam (10s) to form a focused beam (10f).

[0032] The focusing unit (3) is configured to focus a scanning beam (10s) onto a first irradiation plane (X,Z) toward a first focusing point (Fx) located on the irradiation axis (Z) in order to form a focused beam (10f). The first irradiation plane (X,Z) is defined by the irradiation axis (Z) and a first transverse axis (X), where X⊥Z. This type of focusing unit is well known in the art. The present invention is not limited to any particular type of focusing unit (3) as long as it has the ability to focus a scanning beam (10s) toward a first focusing point (Fx) as it is scanned to form a focused beam (10f). For smaller target dimensions, a smaller focusing point (Fx) is required in a corresponding manner.

[0033] As shown in Figure 2, the focusing unit (3) of the scanning beam (10s) may have a lens formed from a focusing magnetic coil (3m) that forms a multipole lens, such as a quadrupole, sextupole, or octupole lens. The focused beam (10f) thus formed still scans in a first transverse direction and optionally in a second transverse direction (X, Y), but as shown in Figure 5(b), the focused beam converges from all points of the scanning pattern toward a first focusing point (Fx). Since the converter is positioned between the focusing unit (3) and the first focusing point (Fx), the focused beam (10f) scans over the scanning area of ​​the conversion unit (4), thereby distributing the energy of the focused beam over a larger scanning area.

[0034] In an embodiment in which the scanning unit (2) is configured to deflect the electron beam (10) along a predefined scanning pattern extending along a first transverse axis (X) and a second transverse axis (Y), the focusing unit (3) may also be configured to focus the scanning beam (10s) onto a second radiation plane (Y,Z) toward a second focusing point (Fy) located on the irradiation axis (Z). The second focusing point (Fy) may be the same as or different from the first focusing point (Fx).

[0035] As shown in Figures 3, 4(a) to 4(c), and 5(a) to 5(c), the half-angle of focus (β) formed at the first focusing point (Fx) between the irradiation axis (Z) and the outer envelope of the focused electron beam may include 20 to 55°, preferably 30 to 45°. When the scanning beam (10s) is scanned over both the first transverse direction and the second transverse direction (X, Y), the half-angle of focus (β) formed at the second focusing point (Fy) may be within the same range as defined above, provided it is different from that of the first focusing point (Fx).

[0036] Conversion unit (4) As shown in Figure 5(a), the conversion unit is conventionally formed by several bremsstrahlung converters (4.1-4.n) having the form of flat sheets of high-Z number metal aligned behind each other along the irradiation axis (Z) and separated from each other by cooling channels. There are two main problems associated with placing such a conversion unit downstream of the focusing unit (3).

[0037] Firstly, as shown in Figure 4(a), electrons located on the outermost edges of the focused beam (10f) intersect the bremsstrahlung converter sheet (4.1) at an intersection angle (α) greater than 90°, while electrons moving along the irradiation axis (Z) intersect the bremsstrahlung converter sheet (4.1) at an intersection angle (α) of 90°. As clearly visible in Figure 4(a) and plotted in Figure 4(d), the length of the bremsstrahlung material traversed by the electrons (Lα) strongly depends on the intersection angle (α), with the minimum distance (L90) located at the intersection angle where α = 90° (see Figure 4(d)). This means that the outermost electrons moving along longer paths (Lα) across the bremsstrahlung material emit greater energy and therefore greater heat than electrons moving closer to L90 or closer to the irradiation axis (Z) with this path length. This is a problem because a temperature gradient exists across the scanning area of ​​the bremsstrahlung converter, and the outermost electrons that emitted greater energy in the first bremsstrahlung sheet have less energy in subsequent sheets than the innermost electrons that move closer to the irradiation axis (Z).

[0038] Secondly, as shown in Figures 5(a), 5(c), and 5(d), the scanning area of ​​each bremsstrahlung sheet traversed by the focused beam (10f) is smaller when the bremsstrahlung sheet is flat than when it is curved. Figure 5 shows a side view or projection on a plane (X,Z), and in the 2D projection of Figure 5, the 2D area in the 3D system is reduced to a 1D length (hi, ci, where i=1~n). Therefore, the term "area" is used when referring to the length hi or ci, so that the reader understands [m 2 To obtain a size in units of ], it becomes possible to mentally multiply lengths hi and ci by the corresponding lengths in the second transverse direction (Y).

[0039] Figure 5(a) shows the scanning area of ​​the bremsstrahlung sheets intersected by the focused electron beam (10f) as a length (hi, where i = 1 to n). Referring to Figure 5(c), the length hi can be calculated as a function of the focusing half-angle (β) as hi = di × sinβ, where di is the distance separating the i-th bremsstrahlung converter (4.i) from the first focusing point (Fx) (measured along the irradiation axis (Z)). Increasing the scanning area of ​​the bremsstrahlung sheets intersected by the focused beam (10f) reduces the scanning area behind each sheet, which increases the concentration of beam energy over smaller scanning areas, and is therefore advantageous, especially when a large number (n) of bremsstrahlung sheets are used.

[0040] The present invention proposes replacing bremsstrahlung converters in the form of flat sheets, which have been used in the art to date, with curved bremsstrahlung converters (4.1-4.n) in the form of a curved sheet, such that the focused beam (10f) intersects each of one or more bremsstrahlung converters by an intersection angle (α) including 65° to 115°, preferably 75° to 105°, at all points. Preferably, the intersection angle is 90°. An intersection angle of 90° at all points of the conversion unit (4) can be obtained by a bremsstrahlung converter in the form of a sheet having a single radius of curvature or optionally a double radius of curvature (di), defined as the distance separating the curved sheet from a first focus point and optionally a second focus point (Fx, Fy). If the first and second focus points are the same, the bremsstrahlung sheet has the shape of a spherical cap of radius (di). This simple solution is • A more uniform heat distribution across the scanning area of ​​the bremsstrahlung sheet where the focused beam (10f) intersects, and • A larger scanning area of ​​the bremsstrahlung sheet where the focused beam (10f) intersects. This solves the two problems mentioned above.

[0041] More uniform heat distribution As shown in Figures 4(b) and 4(c), the intersection angle (α) can be made closer to or equal to 90° by locally tilting the bremsstrahlung sheet by angle γ in relation to the irradiation direction parallel to the irradiation axis (Z). For a sufficiently curved bremsstrahlung sheet, the intersection angle (α) can be reduced to 65° to 115° at all points, preferably 75° to 105° at all points. Referring to Figure 4(d), it can be seen that in the range of intersection angle (α) of 65° to 115° at all points represented by the lightly shaded area, the normalized thickness of the bremsstrahlung material traversed by two electrons of the focused beam (10f) (Lα / L90 = 1 / sinα) can be changed by up to approximately 10% (Lα / L90 ≈ 1.1). When the range of the intersection angle (α) is reduced to 75–105°, represented by the densely shaded area in Figure 4(d), the normalized thickness (Lα / L90) changes by less than 4% for any two electrons in the focused beam (10f) (Lα / L90=1.04). When the intersection angle α=90° at all points, the normalized thickness (Lα / L90=1) is constant for all electrons in the focused beam, and the thermal energy transferred to the bremsstrahlung converter (4.1–4.i) is uniformly distributed across the entire scanning area of ​​the conversion unit (4) traversed by the focused beam (10f) without the involvement of localized areas of higher temperatures.

[0042] In contrast, when the focused beam (10f) crosses the bremsstrahlung flat sheet, for example, at an intersection angle of α = 135° corresponding to the focusing half-angle β = α - 90° = 45°, as shown in Figure 4(a), the normalized thickness of the flat sheet crossed by the focused beam changes over 40% (Lα / L90 = 1.4 in Figure 4(d)), resulting in a proportionally comparable thermal gradient across the scanning area of ​​the flat sheet crossed by the focused beam (10f).

[0043] Using bremsstrahlung converters (4.1-4.n) curved so that the focused beam (10f) intersects each of one or more bremsstrahlung converters (4.1-4.n) at all points with an intersection angle (α) including 65° to 115° clearly contributes to uniformly distributing the heat generated by the interaction with the focused beam across the scanning area of ​​the bremsstrahlung converter. This makes cooling the converter unit easier than in the case of a flat sheet, and thus allows for the successful use of a conventional cooling system (4c).

[0044] Larger scanning area Referring to Figures 5(a) and 5(c), it can be seen that the scanning area represented by the height (hi) of a conversion unit formed by a flat sheet can be characterized by the value hi := di × sinβ, while the scanning area represented by the curved height (ci) of a conversion unit formed by a curved sheet of radius (di) can be characterized by the value ci := di × β. The height ratio (ci / hi) of the curved height (ci) according to the present invention to the height (hi) according to the prior art can be expressed as ci / hi = β / sinβ. In Figure 5(d), the height ratio (ci / hi) is plotted as a function of the half-angle of focus (β). For example, when the half-angle of focus is β = 45°, the curved bremsstrahlung converter has a scanning area (ci) that is 10% larger than that of a flat sheet. When the half-angle of focus is β = 50°, the scanning area is approximately 15% larger. With a curved bremsstrahlung converter, this increased scanning area allows for the dispersion of the focused beam energy over a larger scanning area than a flat converter. Consequently, the heat generated by the interaction between the focused beam and the scanning area of ​​the converter unit is reduced accordingly, which further facilitates the cooling of the converter unit (4).

[0045] Shape of bremsstrahlung converter (4.1-4.n) One or more bremsstrahlung converters (4.1-4.n) may have the shape of a cylindrical section defined by a curved cross-section in a first transverse plane (X,Z) and a generatrix extending along a second transverse axis (Y), where X⊥Y⊥Z. This shape is preferred when the scanning unit (2) is configured to deflect the electron beam (10) along a predefined scanning pattern extending only along the first transverse axis (X). This may also be preferred when the target (5) has a length that defines an elongated shape and the scanning beam does not need to be focused on a plane that includes the length of the elongated target. Figure 1(c) shows a converter unit (4) of this type.

[0046] In one alternative embodiment, one or more bremsstrahlung converters (4.1-4.n) have the form of an oval cap, preferably a spherical cap, defined by a first curved cross section in a first irradiation plane (X,Z) and a second curved cross section in a second irradiation plane (Y,Z). This type of converter unit is shown in Figure 1(b) and is particularly suited when a scanning unit (2) is configured to deflect an electron beam (10) along a predefined scanning pattern extending along a first transverse axis (X) and a second transverse axis (Y), where X⊥Y⊥Z, and further, a focusing unit (3) is configured to focus the scanning beam (10s) onto a second irradiation plane (Y,Z) toward a second focusing point (Fy) located on the irradiation axis (Z), where the second focusing point (Fy) may be the same as or different from the first focusing point (Fx). In one preferred embodiment, the first and second focus points (Fx, Fy) are the same focus point (i.e., Fx = Fy).

[0047] In both embodiments (i.e., single curvature or double curvature), the radius of curvature of the curved section is preferably constant, i.e., defining an arc or a spherical cup. The curvature is preferably close to the distance (di) that separates the bremsstrahlung radiating converter (4.1-4.n) from the first focusing point (Fx).

[0048] In one preferred embodiment, each of the one or more bremsstrahlung converters (4.1-4.n) has a first curved cross section in a first irradiation plane (X,Z) defined by a substantial arc of radius (d1-dn) centered on a first focusing point (Fx). “Substantial arc” is defined herein as a curved segment having a radius of curvature that varies by less than 10% over the length of the curved arc. With this geometry, the focused beam (10f) reaches the bremsstrahlung converter along the first irradiation plane (X,Z) at an intersection angle of 90°.

[0049] In a further preferred embodiment, each of the one or more bremsstrahlung converters (4.1-4.n) has a second curved cross section in a second irradiation plane (Y,Z) defined by a substantial circular arc of radius (d1-dn) centered on a second focal point (Fy). Preferably, the second focal point (Fy) is identical to the first focal point (Fx) (i.e., Fx=Fy), thereby defining the shape of a spherical cap centered on a single focal point (Fx=Fy).

[0050] As shown in Figure 3, the conversion unit (4) has 1 to n bremsstrahlung converters (4.1-4.n) separated from each other by cooling channels, where n includes 2 to 8, preferably 3 to 5. The converter cooling system (4c) may include forced cooling of gas or liquid, in which a cooling fluid flows through cooling channels to draw heat generated by interaction with the focused beam (10f) from the bremsstrahlung converters. This configuration defines what is referred to herein as a “conventional cooling system,” which is well known to those skilled in the art.

[0051] Each of the one or more bremsstrahlung converters (4.1-4.n) has a thickness (L90) measured along a radius of curvature of 3 mm or less, preferably 0.2 to 2.5 mm, more preferably 0.5 to 1.5 mm. The radius of curvature at one point of the bremsstrahlung converter is defined as the radius of the circle that contacts the bremsstrahlung converter at that point and has the same tangent and curvature at that point. Thus, the radius of curvature is perpendicular to the tangent of the bremsstrahlung converter at that point. This is shown in Figures 4(a) to 4(c), as indicated by L90. The thickness (L90) is also the shortest straight line that intersects the bremsstrahlung converter from one surface to the opposite surface.

[0052] In a preferred embodiment, the nth bremsstrahlung converter (4.n) in a sequence of n bremsstrahlung converters positioned closest to the target holder (5h) has a greater thickness (L90) than the first bremsstrahlung converter (4.1) positioned closest to the focusing unit (3). Preferably, each bremsstrahlung converter (4.i) in the sequence is thicker than the adjacent bremsstrahlung converter (4.(i-1)) located upstream (i.e., L90(4.i)>L90(4.(i-1)). Since the scanning area of ​​the bremsstrahlung converters decreases as they get closer to the first focusing point (Fx), increasing the thickness of the bremsstrahlung converters located downstream in the sequence allows for homogenization of the volume of bremsstrahlung converter material interacting with the focused beam (10f). As a result, all bremsstrahlung converters contribute equally to X-ray generation. In addition, the heating generated by the interactions that must be discharged is more evenly distributed among the various bremsstrahlung converters in the conversion unit (4), thereby promoting their cooling.

[0053] 1 to n bremsstrahlung converters (4.1-4.n) can be manufactured from tantalum (Ta), tungsten (W), or titanium (Ti).

[0054] Target (5) and target holder (5h) Due to the use of a focusing unit, the system of the present invention is particularly suitable for small-sized targets (5). Targets (5) are commonly used for diagnostic imaging. 225 To produce Ac, 226 It may be Ra. Other examples of targets that can be used with the system of the present invention to form diagnostic imaging isotopes are: 99m To form Tc 100 Mo target, 187 To generate Re 186 W target, 131 To form I 134 Xe, or 67 To generate Cu 68 Includes Zn and similar materials.

[0055] A target cooling system (5c) is provided, configured to cool the target (5) while it is held in a target holder (5h) as the conversion reaction generated by the interaction of X-rays (11x) with the target generates heat. Similar to the converter cooling system (4c) described above, the target cooling system (5c) may include forced cooling of a gas or liquid through a cooling channel in thermal contact with the target (5). Naturally, it is important to maintain the temperature of the target (5) below the degradation temperature.

[0056] When the first and second focusing points are identical (i.e., Fx = Fy), and the X-rays generated by the conversion unit (4) in this manner converge toward a small focusing area around the focusing point (Fx), the sample holder can be configured to move the target (5) so that a larger area of ​​the target is scanned by the (stationary) focusing point. This is particularly interesting for larger-dimension targets, where the exposure area is larger than the X-ray focusing area, so that the conversion occurs over a larger area / volume of the target than would occur if it remained stationary.

[0057] Processes that produce radioactive isotopes The system of the present invention can be used in a process of generating radioactive isotopes by X-ray irradiation of a target. The process has the steps of providing the system described above. After loading the target (5) onto the target holder (5h), an accelerated electron beam is scanned and focused onto the conversion unit (4) to generate X-rays so as to irradiate the target with the X-rays thus generated.

[0058] The target is, for example, 225 To generate Ac 226 Ra, 99m To form Tc 100 Mo target, 187 To generate Re 186 W target, 131 To form I 134 Xe, or 67 To generate Cu 68 Zn and similar substances are acceptable. [Explanation of Symbols]

[0059] 1 Electron accelerator 2 scanning units 2m scanning magnetic coil 3 Focusing Unit 3m Focusing Magnetic Coil 4 Conversion Units 4.1~4.n Bremsstrahlung Converters 4C converter cooling system 5 Targets 5c Target Cooling System 5h Target Holder 10 Electron beam 10f Focused beam 10s scanning beam 11x photon beam c1~cn: Length of the cross-section of the curved bremsstrahlung converter irradiated by the focused beam. d1~dn Distance between the i-th bremsstrahlung converter and the first focus point Fx, Fy Focus points of the focused beam along the first and second irradiation planes (X,Z) and (Y,Z) h1~hn: Length of the cross-section of the straight bremsstrahlung converter irradiated by the focused beam. L90 Thickness of the bremsstrahlung converter, measured perpendicular to its surface. Lα is the thickness of the bremsstrahlung converter, measured along the angle α between it and the surface. X First transverse axis Y Second Transverse Axis Z irradiation axis α is the angle between the focused beam and the surface of the bremsstrahlung converter. β Focus half-angle of the focused beam between the irradiation axis (Z) and the focusing point γ: Angle between the surface of the bremsstrahlung converter and the irradiation axis (Z).

Claims

1. A system for the production of radioactive isotopes, - An electron accelerator (1) configured to generate an electron beam (10) of electrons accelerated along the irradiation axis (Z), A scanning unit (2) is configured to deflect the electron beam (10) along a predetermined scanning pattern in order to form a scanning beam (10s), - A focusing unit (3) having one or more magnets configured to focus the scanning beam (10s) onto a first irradiation plane (X, Z) toward a first focusing point (Fx) located on the irradiation axis (Z) in order to form a focused beam (10f), wherein the first irradiation plane (X, Z) is defined by the irradiation axis (Z) and the first transverse axis (X), and X⊥Z, and the focusing unit (3) - A conversion unit (4) having one or more bremsstrahlung converters (4.1-4.n) positioned between the focusing unit (3) and the first focusing point (Fx), configured to convert the focused beam (10f) into a photon beam (11x), - A converter cooling system (4c) configured to cool one or more of the aforementioned bremsstrahlung converters (4.1-4.n), A target holder (5h) configured to hold the target (5), It has, The electron accelerator (1), the scanning unit (2), the focusing unit (3), the conversion unit (4), and the target holder (5h) are all aligned along the irradiation axis (Z) and are arranged downstream of each other in this order, where "downstream" is defined in relation to the electron beam direction, in this system, The system is characterized in that the one or more bremsstrahlung converters (4.1-4.n) are curved such that the focused beam (10f) intersects each of the one or more bremsstrahlung converters (4.1-4.n) at an intersection angle (α) of 65° to 115°, preferably 75° to 105° at all points.

2. In the system described in claim 1, - The scanning unit (2) is configured to deflect the electron beam (10) along the predefined scanning pattern extending along the first transverse axis (X) and the second transverse axis (Y), where X⊥Y⊥Z, - The focusing unit (3) is configured to focus the scanning beam (10s) on the second irradiation plane (Y, Z) toward the second focusing point (Fy) located on the irradiation axis (Z), and the second focusing point (Fy) may be the same as or different from the first focusing point (Fx). - A system characterized in that one or more bremsstrahlung converters (4.1-4.n) have the shape of an oval cap, preferably a spherical cap, defined by a first curved cross section in the first irradiation plane (X, Z) and a second curved cross section in the second irradiation plane (Y, Z).

3. In the system described in claim 1, - The scanning unit (2) is configured to deflect the electron beam (10) along the predefined scanning pattern that extends only along the first transverse axis (X), A system characterized in that one or more bremsstrahlung converters (4.1-4.n) have the shape of a cylindrical section defined by a curved cross section in the first irradiation plane (X, Z) and a generatrix extending along the second transverse axis (Y), wherein X⊥Y⊥Z.

4. In the system according to any one of claims 1 to 3, The system is characterized in that the focusing unit (3) is configured to form the focusing beam (10f), and the focusing half-angle (β) formed at the first focusing point (Fx) with the irradiation axis (Z) on the first irradiation plane (X, Z) includes 20 to 55°, preferably 30 to 45°.

5. In the system described in claim 2, The system is characterized in that each of the one or more bremsstrahlung converters (4.1-4.n) has a first curved cross section in the first irradiation plane (X, Z) defined by a substantial arc of radius (d1-dn) centered on the first focusing point (Fx), wherein the "substantial arc" is defined as a curved segment having a radius of curvature that changes by only 10% or less over the length of the curved cross section.

6. In the system described in claim 5, A system characterized in that each of the one or more bremsstrahlung converters (4.1-4.n) has a second curved cross section in the second irradiation plane (Y, Z) defined by a substantial arc of radius (d1-dn) centered on the second focusing point (Fy), wherein the second focusing point (Fy) is preferably the same as the first focusing point (Fx) (i.e., Fx = Fy).

7. In the system according to any one of claims 1 to 3, The system is characterized in that each of the one or more bremsstrahlung radiating converters (4.1-4.n) has a thickness (L90) measured along a radius of curvature of 3 mm or less, preferably the thickness (L90) is 0.2 to 2.5 mm, more preferably 0.5 to 1.5 mm.

8. In the system according to any one of claims 1 to 3, The system is characterized in that the nth bremsstrahlung converter (4.n), which is positioned closest to the target holder (5h), has a greater thickness (L90) than the first bremsstrahlung converter (4.1), which is positioned closest to the focusing unit (3).

9. In the system according to any one of claims 1 to 3, The system is characterized in that the conversion unit (4) has 1 to n bremsstrahlung converters (4.1-4.n) separated from each other by cooling channels, where n includes 2 to 8, preferably 3 to 5.

10. In the system according to any one of claims 1 to 3, The converter cooling system (4c) is characterized by having forced cooling of gas or liquid.

11. In the system according to claim 10, A system characterized in that one or more of the aforementioned bremsstrahlung converters (4.1-4.n) are manufactured from tantalum (Ta), tungsten (W), or titanium (Ti).

12. In the process of generating radioactive isotopes by irradiating a target with X-rays, - The step of providing the system according to any one of claims 1 to 3, - The step of loading the target onto the target holder (5h), - The steps include scanning and focusing the accelerated electron beam onto the conversion unit (4) in order to generate X-rays, - The step of irradiating the target with the X-rays generated in this manner, A process characterized by having the following:

13. In the process described in claim 12, The target (5) is ２２５ for generating Ac ２２６ Ra, ９９ｍ for forming Tc １００ Mo, １８７ for generating Re １８６ W, １３１ for forming I １３４ Xe, or ６７ for generating Cu ６８ a process characterized by being selected from one of Zn.

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