System for production of radioisotopes by bremsstrahlung comprising 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 radioisotopes by irradiating a target with X-rays formed by bremsstrahlung when a converter is directed at a high-energy electron beam. In particular, the invention relates to a particular converter geometry that reduces the heat generated by the electron beam and allows conventional cooling systems to be used to maintain the temperature of the converter within acceptable boundaries. [Background technology]

[0002] Radioisotopes can be produced by a variety of reactions, using charged particles or using photonuclear reactions (e.g., X-rays). For example: 225 Ac is 226 Formed by photonuclear reactions caused by irradiation of Ra targets with X-rays 225 It can be prepared by the decay of Ra. To form the desired isotope, the energy of the X-rays must be precisely controlled, which is directly dependent on the energy of the electron beam. 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 produced by irradiating a converter with a high-energy electron beam. The converter comprises a source of the high-energy electron beam, which includes an electron accelerator such as a roadtron or linear accelerator, and a target (in this example, 226The converter is positioned between the target and the electron beam (Ra). The converter is formed from a foil of a high-Z metal such as Ti or Ta. As the converter is irradiated by the electron beam, the electron beam slows down and the released energy is converted into X-ray radiation that reaches the target to form the desired radioisotope. This mechanism is called "bremsstrahlung".

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

[0005] To improve cooling of the converter and / or to allow a wider geometric spread of the resulting photon beam by the converter, US Pat. No. 6,223,669 proposes scanning the electron beam over the scanning area of ​​the converter by using a magnetic scanning coil. US Pat. No. 6,223,669 combines the scanning of the electron beam with a translational movement of the target synchronized with the scanning of the electron beam so that the target is continuously exposed to the full intensity of the bremsstrahlung generated by the converter.

[0006] US Patent No. 5,649,999 describes a focusing lens used to collimate or focus an electron beam. Collimation of an electron beam is useful because a diverging electron beam increases the divergence of the generated photons. This would in turn require a larger target to collect the photons. The focusing lens can be formed from a magnet and can be a multipole lens, such as a quadrupole, hexapole, or octopole lens. [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 above-mentioned improvements, it remains a problem to sufficiently cool the converter with conventional cooling systems to prevent premature thermal degradation of the converter. 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 radiation. The solution proposed by the present invention to achieve this dual objective is described below. Summary of the Invention

[0009] The invention is defined in the accompanying independent claims. Preferred embodiments are defined in the dependent claims. In particular, the invention relates to a system for the production of radioisotopes, comprising: an electron accelerator configured to generate an electron beam of electrons accelerated along an irradiation axis (Z); a scanning unit configured to deflect the electron beam along a predefined scan pattern to form a scanned beam; a focusing unit having one or more magnets configured to focus the scanning beam onto a first illumination plane (X,Z) towards a first focusing point (Fx) arranged on an illumination axis (Z) to form a focused beam, the first illumination plane (X,Z) being defined by the illumination axis (Z) and a first transverse axis (X), where X⊥Z; a conversion unit arranged between the focusing unit (3) and the first focusing point (Fx) and having one or more bremsstrahlung converters (4.1-4.n) configured to convert the focused beam into a photon beam; a converter cooling system configured to cool one or more bremsstrahlung converters; a target holder configured to hold a target; It has.

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

[0011] In a first embodiment, the scanning unit is configured to deflect the electron beam along a predefined scan 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 illumination plane (Y,Z) towards a second focusing point (Fy) arranged on the illumination axis (Z). The second focusing point (Fy) can be identical to the first focusing point (Fx) or can be different. The one or more bremsstrahlung converters have the shape of an oval cap, preferably a spherical cap, defined by a first curved cross section in the first illumination plane (X,Z) and by a second curved cross section in the second illumination plane (Y,Z).

[0012] Each of the one or more bremsstrahlung converters preferably has a first curved cross-section in a first illumination plane (X, Z) defined by a substantially circular arc of radius (d1-dn) centered on a first focal point (Fx). A "substantially circular arc" is defined herein as a curved segment having a radius of curvature that varies by 10% or less over the length of the curved cross-section. Alternatively or additionally, each of the one or more bremsstrahlung converters preferably has a second curved cross-section in a second illumination plane (Y, Z) defined by a substantially circular 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 a second embodiment, the scanning unit is configured to deflect the electron beam along a predefined scan pattern extending only along a first transverse axis (X). The one or more bremsstrahlung converters have the shape of a section of a cylinder defined by a curved cross-section in the first transverse plane (X,Z) and a generatrix extending along the second transverse axis (Y), where X⊥Y⊥Z. Each of the one or more bremsstrahlung converters preferably has a first curved cross-section in the first illumination plane (X,Z) defined by a substantially circular arc of radius (d1-dn) centered on the first focal point (Fx).

[0014] The focusing unit may be configured to form a focused beam having a focusing half angle (β) formed at a first focusing point (Fx) with an illumination axis (Z) on a first illumination plane (X, Z) of 20 to 55°, preferably 30 to 45°.

[0015] The one or more bremsstrahlung converters may be made from tantalum (Ta) or tungsten (W) or titanium (Ti). Each of the one or more bremsstrahlung converters has a thickness (L90) measured along the radius of curvature that is preferably less than or equal to 3 mm, preferably the thickness (L90) is comprised between 0.2 and 2.5 mm, more preferably between 0.5 and 1.5 mm. It is further preferred that the nth bremsstrahlung converter located closest to the target holder has a greater thickness (L90) than the first bremsstrahlung converter located closest to the focusing unit.

[0016] The conversion unit may comprise 1 to n bremsstrahlung converters separated from each other by cooling channels, n being comprised between 2 and 8, preferably between 3 and 5. The converter cooling system may comprise a forced cooling flow of gas or liquid through the channels.

[0017] The present invention also relates to a process for producing 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 the accelerated electron beam onto the conversion unit to generate X-rays; irradiating a target with the X-rays thus generated; It has.

[0018] The target is 225 To generate Ac 226 Ra, 99m To form Tc 100 Mo, 187 To generate Re 186 W, 131 To form I 134 Xe, or 67 To generate Cu 68 Zn.

[0019] For a fuller understanding of the nature of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0020] [Figure 1a] FIG. 1(a) shows a side view of a system according to the present invention. [Figure 1b] FIG. 1(b) shows a perspective view of a first embodiment of a system according to the invention. [Figure 1c] FIG. 1(c) shows a perspective view of a second embodiment of a system according to the present invention. [Figure 2] FIG. 2 shows a diagram of a scanning and focusing unit according to the invention. [Figure 3] FIG. 3 shows an example of a conversion unit according to the invention. [Figure 4a] FIG. 4(a) shows the maximum distance (Lα) traversed by the electron beam across a straight sheet of a prior art bremsstrahlung converter, where α=β+90°. [Figure 4b] FIG. 4(b) shows the maximum distance (Lα) traversed by the electron beam across the curved sheet of a bremsstrahlung converter according to the invention, where 65°≦α≦115°. [Figure 4c] FIG. 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] FIG. 4(d) plots the normalized maximum distance (Lα / L90) traversed by the electron beam across the curved sheet of a bremsstrahlung converter according to the invention as a function of angle α, with the lowest value of Lα being L90 at α=90°. [Figure 5a] FIG. 5(a) shows the height (hi) representing the scan area of ​​a prior art straight bremsstrahlung converter traversed by the scanning beam. [Figure 5b]FIG. 5(b) shows the height (ci) representing the scan area of ​​a curved bremsstrahlung converter according to the present invention traversed by the scanning beam. [Figure 5c] FIG. 5(c) compares the height (hi, ci) of the bremsstrahlung converter traversed by the scanning beam according to the prior art with 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). DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention relates to a system for producing radioisotopes by converting an electron beam into a photon beam and irradiating a target (5) with the photon beam. The system comprises an electron accelerator (1) configured to generate an electron beam (10) of electrons accelerated along an 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 predefined scan pattern to form a scanned 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 the scanning beam (10s) onto a first illumination plane (X,Z) towards a first focusing point (Fx) arranged on the illumination axis (Z) to form a focused beam (10f), the first illumination plane (X,Z) being defined by the illumination axis (Z) and a first transverse axis (X), where X⊥Z.

[0022] The conversion unit (4) is arranged 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 the 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 focus point (Fx), and is equipped with a target cooling unit (5c) configured to cool the target (5) when held in 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 arranged downstream of each other in that order, with "downstream" being defined in relation to the electron beam direction.

[0025] The gist of the present invention is that the bremsstrahlung converter(s) (4.1-4.n) are curved in such a way that the focused beam (10f) intersects with each of the bremsstrahlung converter(s) (4.1-4.n) by an intersection angle (α) comprised at all points between 65° and 115°, preferably at all points between 75° and 105°, 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, so long as it is capable of generating an electron beam (10) with an energy between 10 and 40 MeV, preferably between 15 and 30 MeV, and preferably between 20 and 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-like accelerator (e.g., a roadtron).

[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, so long as it is capable of scanning the electron beam (10) along a predefined scan pattern to form the scanned beam (10s). When impinging on 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 the small scan area of ​​the converter.

[0028] The scanning unit (2) may be equipped with a scanning magnetic coil (2m) transverse to 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 scan area along first and second transverse directions (X, Y), as shown in Figure 1(b).

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

[0030] As described above, scanning the electron beam in a first transverse direction and optionally a second transverse direction over the converter facilitates cooling of the converter. However, this results in a wider 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, 226The wide geometrical spread of the X-rays can be a disadvantage when targets of small dimensions such as Ra are used, and for this reason it has been proposed in the art to use a focusing unit to converge the scanning beam (10s) to focus the beam onto the converter via a focusing magnetic coil (3m).

[0031] Focusing unit (3) Therefore, the scanning beam (10s) cannot be used efficiently for targets with smaller dimensions, because the photon beam (11x) formed by the interaction of the scanning electron beam with the conversion unit (4) also spreads. For targets with small dimensions, refocusing of the scanning beam (10s) or the photon beam (11x) is required. Focusing of the photon beam (11x) is described, for example, in U.S. Pat. No. 5,699,499. In the present invention, the system has a focusing unit (3) arranged 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 the scanning beam (10s) onto a first illumination plane (X, Z) toward a first focal point (Fx) located on the illumination axis (Z) to form a focused beam (10f). The first illumination plane (X, Z) is defined by the illumination axis (Z) and a first transverse axis (X), where X⊥Z. Focusing units of this type are well known in the art. The present invention is not limited to any particular type of focusing unit (3), as long as it is capable of focusing the scanning beam (10s) toward the first focal point (Fx) as it is scanned to form the focused beam (10f). For targets with smaller dimensions, a focusing point (Fx) with correspondingly smaller dimensions is required.

[0033] As shown in FIG. 2, the focusing unit (3) of the scanning beam (10s) can have a lens formed from focusing magnetic coils (3m) that form a multipole lens, such as a quadrupole, hexapole, or octapole lens. The focused beam (10f) thus formed still scans in a first transverse direction and optionally a second transverse direction (X, Y), but as shown in FIG. 5(b), the focused beam converges from all points of the scan pattern toward the first focusing point (Fx). Because 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 scan 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) towards a second focusing point (Fy) arranged on the irradiation axis (Z), which may be identical to or different from the first focusing point (Fx).

[0035] 3, 4(a)-4(c), and 5(a)-5(c), the focusing half angle (β) formed at the first focusing point (Fx) between the illumination axis (Z) and the outer envelope of the focused electron beam may be in the range of 20-55°, preferably 30-45°. When the scanning beam (10s) is scanned across both the first and second transverse directions (X, Y), the focusing half angle (β) formed at the second focusing point (Fy) may be in the same range as defined above, provided that it is different from 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) in the form of flat sheets of high-Z metal aligned behind each other along the illumination axis (Z) and separated from each other by cooling channels. There are two main problems with locating such a conversion unit downstream of the focusing unit (3).

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

[0038] Second, as shown in Figures 5(a), 5(c), and 5(d), the scan 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 the plane (X,Z), and in the 2D projection of Figure 5, the two-dimensional area in the 3D system is reduced to one-dimensional lengths (hi, ci, where i = 1 to n). Therefore, when referring to lengths hi or ci, the term "area" is used, which allows the reader to understand [m 2 It is then possible to mentally multiply the lengths hi and ci by the corresponding lengths in the second transverse direction (Y) to obtain the magnitude in units of ].

[0039] In Figure 5(a), the scan area of ​​a bremsstrahlung sheet intersected by the focused electron beam (10f) is represented by 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 × sin β, where di is the distance separating the i-th bremsstrahlung converter (4.i) from the first focusing point (Fx) (measured along the illumination axis (Z)). Increasing the bremsstrahlung scan area intersected by the focused beam (10f) can be advantageous, especially when multiple (n) bremsstrahlung sheets are used, as it reduces the scan area after each sheet, thereby increasing the concentration of the beam energy over a smaller scan area.

[0040] The present invention proposes replacing the bremsstrahlung converters in the form of flat sheets used up to now in the art by curved bremsstrahlung converters (4.1-4.n) in the form of a curved sheet such that the focused beam (10f) intersects with each of one or more bremsstrahlung converters by an intersection angle (α) comprised between 65° and 115° at all points, preferably between 75° and 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 with a single or optionally double radius of curvature (di), defined as the distance separating the curved sheet from the first and optionally second focusing points (Fx, Fy). If the first and second focusing points are identical, the bremsstrahlung sheet has the shape of a spherical cap of radius (di). This simple solution is a more uniform heat distribution across the scan area of ​​the bremsstrahlung sheet intersected by the focused beam (10f), and Larger scanning area of ​​the bremsstrahlung sheet intersected by the focused beam (10f), This solves the two problems mentioned above.

[0041] More even 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 an angle γ with respect to the illumination direction parallel to the illumination axis (Z). With a sufficiently curved bremsstrahlung sheet, the intersection angle (α) can be reduced to 65°-115° everywhere, preferably 75°-105° everywhere. Referring to Figure 4(d), it can be seen that in the range of intersection angles (α) between 65°-115° everywhere, represented by the lightly shaded area, the normalized thickness (Lα / L90 = 1 / sinα) of the bremsstrahlung material traversed by the two electrons of the focused beam (10f) can vary by a maximum of about 10% (Lα / L90 ≈ 1.1). When the intersection angle (α) range is reduced to 75-105°, represented by the darkly shaded area in Figure 4(d), the normalized thickness (Lα / L90) changes by less than 4% (Lα / L90 = 1.04) for any two electrons in the focused beam (10f). For an 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 converters (4.1-4.i) is uniformly distributed across the entire scan area of ​​the conversion unit (4) traversed by the focused beam (10f) without localized areas of higher temperature.

[0042] In contrast, when a focused beam (10f) traverses a bremsstrahlung flat sheet as shown in FIG. 4(a) with an intersection angle of, for example, α=135°, corresponding to a focusing half angle β=α-90°=45°, the normalized thickness of the flat sheet traversed by the focused beam varies by 40% (in FIG. 4(d) Lα / L90=1.4), which results in proportionally comparable thermal gradients across the scan area of ​​the flat sheet traversed by the focused beam (10f).

[0043] The use of curved bremsstrahlung converters (4.1-4.n) such that the focused beam (10f) intersects each of one or more bremsstrahlung converters (4.1-4.n) at every point by an intersection angle (α) comprised between 65° and 115° clearly contributes to homogenizing the heat generated by the interaction with the focused beam over the scanning area of ​​the bremsstrahlung converter, which makes the cooling of the conversion unit easier than in the case of a flat sheet, and therefore allows the use of conventional cooling systems (4c) successfully.

[0044] Larger scanning area 5(a) and 5(c), it can be seen that the scanning area represented by the height (hi) of the conversion unit formed by the flat sheet can be characterized by the value hi:=di×sinβ, while the scanning area represented by the curved height (ci) of the conversion unit formed by the curved sheet of radius (di) can be characterized by the value ci:=di×β. The height ratio (ci / hi) of the curved height (ci) of the present invention to the height (hi) of the prior art can be expressed as ci / hi=β / sinβ. In FIG. 5(d), the height ratio (ci / hi) is plotted as a function of the focusing half angle (β). For example, it can be seen that when the focusing half angle is β=45°, the curved bremsstrahlung converter has a scanning area (ci) that is 10% larger than that of the flat sheet. When the focusing half angle is β=50°, the scanning area is approximately 15% larger. With a curved bremsstrahlung converter, this increased scanning area allows the focused beam energy to be distributed over a larger scanning area than with a flat one, and therefore the heat generated by the interaction of the focused beam with the scanning area of ​​the conversion unit is correspondingly reduced, thereby further facilitating cooling of the conversion 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 section of a cylinder 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 containing the length of the elongated target. Figure 1(c) shows a conversion unit (4) of this type.

[0046] In an 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 illumination plane (X,Z) and by a second curved cross section in a second illumination plane (Y,Z). This type of conversion unit is shown in Fig. 1(b) and is particularly adapted for the case where 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), where X⊥Y⊥Z, and further the focusing unit (3) is configured to focus the scanning beam (10s) onto a second illumination plane (Y,Z) towards a second focusing point (Fy) arranged on the illumination axis (Z), which may be identical to or different from the first focusing point (Fx). In a preferred embodiment, the first focus point and the second focus point (Fx, Fy) are the same focus point (ie, Fx=Fy).

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

[0048] In a preferred embodiment, each of the one or more bremsstrahlung converters (4.1-4.n) has a first curved cross-section in the first illumination plane (X,Z) defined by a substantially circular arc of radius (d1-dn) centered on the first focal point (Fx). A "substantially circular 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 arc. According to this geometry, the focused beam (10f) reaches the bremsstrahlung converter along the first illumination plane (X,Z) with 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 the second illumination plane (Y,Z) defined by a substantially circular arc of radius (d1-dn) centred on a second focal point (Fy), which is preferably identical to the first focal point (Fx) (i.e. Fx=Fy), thereby defining the shape of a spherical cap centred on a single focal point (Fx=Fy).

[0050] As shown in Figure 3, the conversion unit (4) comprises 1 to n bremsstrahlung converters (4.1-4.n) separated from each other by cooling channels, where n is between 2 and 8, preferably between 3 and 5. The converter cooling system (4c) may comprise forced cooling of a gas or liquid, with a cooling fluid flowing through the cooling channels to extract heat from the bremsstrahlung converters generated by their interaction with the focused beam (10f). 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 of a bremsstrahlung converter at a point is defined as the radius of a circle that touches the bremsstrahlung converter at that point and has the same tangent and curvature at that point. The radius of curvature is therefore 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 the sequence of n bremsstrahlung converters, which is arranged closest to the target holder (5h), has a greater thickness (L90) than the first bremsstrahlung converter (4.1), which is arranged 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 ​​a bremsstrahlung converter decreases as the bremsstrahlung converter approaches 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). This results in all bremsstrahlung converters contributing equally to the production of X-rays. Furthermore, the heating generated by the interactions that must be removed is also more evenly distributed among the various bremsstrahlung converters of the conversion unit (4), thereby facilitating their cooling.

[0053] The bremsstrahlung converters 1 to n (4.1-4.n) can be made 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 targets (5) of small size, such as those commonly used for diagnostic imaging. 225 To generate Ac, 226 Other examples of targets that can be used with the system of the present invention to form diagnostic imaging isotopes include: 99m To form Tc 100 Mo target, 187 To generate Re 186 Double target, 131 To form I 134 Xe, or 67 To generate Cu 68 Includes Zn and similar.

[0055] A target cooling system (5c) is provided that is configured to cool the target (5) while held within the target holder (5h) as the conversion reaction generated by the interaction of the x-rays (11x) with the target generates heat. Similar to the converter cooling system (4c) described above, the target cooling system (5c) can comprise gas or liquid forced cooling, in which a cooling fluid flows through cooling channels in thermal contact with the target (5). Of course, it is important to maintain the temperature of the target (5) below its degradation temperature.

[0056] When the first and second focusing points are identical (i.e. Fx=Fy) and the X-rays thus generated by the conversion unit (4) are focused towards 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 targets of larger dimensions, whose exposed area is larger than the focusing area of ​​the X-rays, so that conversion occurs over a larger area / volume of the target than if it remained stationary.

[0057] The process of producing radioisotopes The system of the present invention can be used in a process for producing radioisotopes by X-ray irradiation of a target, comprising the steps of providing the system described above, in which a target (5) is loaded onto a target holder (5h), and then an accelerated electron beam is scanned and focused onto a conversion unit (4) to generate X-rays such that the X-rays thus generated irradiate the target.

[0058] The target is, for example, 225 To generate Ac 226 Ra, 99m To form Tc 100 Mo target, 187 To generate Re 186 Double target, 131 To form I 134 Xe, or 67 To generate Cu 68 It may be Zn and the like. [Explanation of symbols]

[0059] 1 Electron accelerator 2 Scanning Unit 2m scanning magnetic coil 3 Focusing unit 3m focusing magnetic coil 4 Conversion Unit 4.1~4.n Bremsstrahlung Converter 4c Converter Cooling System 5. Target 5c Target Cooling System 5h target holder 10 Electron Beam 10f focused beam 10s scanning beam 11x photon beam c1-cn: the cross-sectional lengths of a curved bremsstrahlung converter illuminated by a focused beam d1~dn: distance between the ith bremsstrahlung converter and the first focusing point Fx, Fy Focus points of the focused beam along the first and second illumination planes (X,Z) and (Y,Z) h1~hn: the cross-sectional length of a straight bremsstrahlung converter illuminated by a focused beam L90: The thickness of the bremsstrahlung converter measured perpendicular to its surface Lα: The thickness of the bremsstrahlung converter measured along the angle α between it and its surface X First transverse axis Y Second transverse axis Z irradiation axis α is the angle between the focused beam and the bremsstrahlung converter surface β Focusing half angle of the focused beam between the illumination axis (Z) at the focusing point γ is the angle between the surface of the bremsstrahlung converter and the irradiation axis (Z)

Claims

1. 1. A system for the production of radioisotopes, comprising: an electron accelerator (1) configured to generate an electron beam (10) of electrons accelerated along an irradiation axis (Z); a scanning unit (2) configured to deflect said electron beam (10) along a predefined scanning pattern 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 illumination plane (X, Z) towards a first focusing point (Fx) arranged on the illumination axis (Z) to form a focused beam (10f), the first illumination plane (X, Z) being defined by the illumination axis (Z) and a first transverse axis (X), where X⊥Z; a conversion unit (4) arranged between the focusing unit (3) and the first focusing point (Fx) and comprising one or more bremsstrahlung converters (4.1-4.n) configured to convert the focused beam (10f) into a photon beam (11x); a converter cooling system (4c) configured to cool said one or more bremsstrahlung converters (4.1-4.n); a target holder (5h) configured to hold a target (5); and a system in which 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 arranged downstream of each other in this order, with "downstream" being defined in relation to the electron beam direction; 1. The system according to claim 1, wherein the one or more bremsstrahlung converters (4.1-4.n) are arranged such that the focused beam (10f) is curved such that it intersects each of the one or more bremsstrahlung converters (4.1-4.n) by an intersection angle (α) which is between 65° and 115° at all points, preferably between 75° and 105° at all points.

2. 10. The system of claim 1, the scanning unit (2) is configured to deflect the electron beam (10) along the predefined scan 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) also onto a second illumination plane (Y, Z) towards a second focusing point (Fy) arranged on the illumination axis (Z), which second focusing point (Fy) can be identical to or different from the first focusing point (Fx); A system characterized in that said 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 said first illumination plane (X,Z) and by a second curved cross section in said second radiation plane (Y,Z).

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

4. 4. The system according to claim 1, wherein: The focusing unit (3) is configured to form the focused beam (10f), and a focusing half angle (β) formed at the first focusing point (Fx) with the illumination axis (Z) on the first illumination plane (X, Z) is comprised between 20 and 55°, preferably between 30 and 45°.

5. 4. The system according to claim 1, wherein:

1. A system comprising: one or more bremsstrahlung controllers (4.1-4.n) each having a first curved cross-section in the first illumination plane (X, Z) defined by a substantially circular arc of radius (d1-dn) centered on the first focal point (Fx), wherein a "substantially circular arc" is defined as a curved segment having a radius of curvature that varies by 10% or less over the length of the curved cross-section.

6. 6. The system of claim 5, wherein each of said one or more bremsstrahlung converters (4.1-4.n) has a second curved cross-section in said second illumination plane (Y,Z) defined by a substantially circular arc of radius (d1-dn) centered on said second focal point (Fy), said second focal point (Fy) preferably being identical to said first focal point (Fx) (i.e. Fx=Fy).

7. 4. The system according to claim 1, wherein:

1. A system wherein each of said one or more bremsstrahlung converters (4.1-4.n) has a thickness (L90) measured along a radius of curvature of less than or equal to 3 mm, preferably said thickness (L90) being between 0.2 and 2.5 mm, more preferably between 0.5 and 1.5 mm.

8. 4. The system according to claim 1, wherein:

1. A system characterized in that the nth bremsstrahlung converter (4.n) arranged closest to the target holder (5h) has a thickness (L90) greater than the first bremsstrahlung converter (4.1) arranged closest to the focusing unit (3).

9. 4. The system according to claim 1, wherein: A system characterized in that said conversion unit (4) comprises 1 to n bremsstrahlung converters (4.1-4.n) separated from each other by cooling channels, n being comprised between 2 and 8, preferably between 3 and 5.

10. 4. The system according to claim 1, wherein: The converter cooling system (4c) comprises gas or liquid forced cooling.

11. 11. The system of claim 10, A system characterized in that said one or more bremsstrahlung converters (4.1-4.n) are made from tantalum (Ta), tungsten (W) or titanium (Ti).

12. In a process for producing radioisotopes by X-ray irradiation of a target, - providing a system according to any one of claims 1 to 3; - loading a target onto said target holder (5h); - scanning and focusing an accelerated electron beam onto said conversion unit (4) to generate X-rays; - irradiating the target with the x-rays thus produced; A process comprising:

13. 13. The process of claim 12, The target (5) ２２５ To generate Ac ２２６ Ra, ９９ｍ To form Tc １００ Mo, １８７ For generating Re １８６ W. １３１ To form I １３４ Xe, or ６７ For producing Cu ６８ Zn.

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