Device for producing radioisotopes

Abstract

The invention relates to a device (1) for producing radioisotopes by irradiating a target fluid using a particle beam (13). This device comprises an irradiation cell (7) that includes a cavity (3) for receiving the target fluid. A non-cryogenic cooling device cools the walls of the cavity (3). The cavity (3) has an inclined surface (15) downwardly delimiting the cavity (3) so as to evacuate the target fluid, which condenses on contact with the cooled walls, under gravity towards a metal foil (4) which closes off this cavity (3). The inclined surface (15) intersects the plane formed by the metal foil (4), making an acute angle (a) with said plane, so as to form with the metal foil (4) a wedge-shaped zone (18) capable of collecting, by gravity, the condensed target fluid.

Claims

1. A device configured to produce radioisotopes by irradiating a target fluid using a particle beam, the target fluid comprising a radioisotope precursor, the device comprising: an irradiation cell comprising: a conical cavity configured to contain the target fluid, the cavity having an opening at a base of the conical cavity, where the cavity base is surrounded by a front surface of the irradiation cell; and a metal foil connected to the front surface of the irradiation cell and closing the opening of the cavity, wherein the metal foil has a diameter less than or substantially equal to a diameter of the cavity base, wherein an outer surface of the conical cavity comprises furrows extending from an area close to an apex of the conical cavity toward a region close to the base of the cavity, so as to create pathways for the passage of non-cryogenic coolant to flow along the outer surface; a cooling device configured to circulate the non-cryogenic coolant and to cool the walls of the cavity; and an inclined surface, defining the bottom surface of the cavity, so as to evacuate the target fluid, which condenses in contact with the cavity walls, by gravity toward the metal foil; wherein the inclined surface intersects a plane formed by the metal foil at an acute angle () with the plane, so as to form, with the metal foil, a corner-shaped area that collects the evacuated target fluid, such that a height of the collected target fluid is maximal at the metal foil and decreases in a direction away from the metal foil.

2. The device according to claim 1, wherein the metal foil is positioned substantially perpendicular to an axis of the particle beam.

3. The device according to claim 1, wherein the radioisotopes are produced by irradiating a target fluid using a substantially horizontal particle beam.

4. The device according to claim 1, wherein a size of the acute angle () is between 30 and 89.

5. The device according to claim 1, wherein the cooling device comprises: a coolant intake situated across from the part of the irradiation cell opposite the foil; and a diffuser creating a channel disposed to circulate the non-cryogenic coolant.

6. The device according to claim 1, wherein an apex of conical cavity is rounded.

7. The device according to claim 1, wherein the irradiation cell comprises: a first part comprising a front surface, which forms a bearing surface for the metal foil, and a rear surface; and a second, substantially conical part, which protrudes relative to the rear surface of the first part; wherein the cavity: passes through the first part to extend into the second part, and forms, in the front surface of the first part, an opening defined by an edge, such that the metal foil closes the opening at the edge when the metal foil bears on the front surface of the first part.

8. The device according to claim 7, wherein the first part further comprises a groove surrounding the second part on a side of the rear surface, the groove being configured to collect the non-cryogenic coolant flowing along an outer surface of the second part.

9. The device according to claim 1, wherein the irradiation cell is made from niobium.

10. An irradiation cell configured to produce radioisotopes by irradiating a target fluid using a particle beam, the target fluid comprising a radioisotope precursor, the irradiation cell comprising: a metal foil; a first part comprising a front surface and a rear surface, the front surface forming a bearing surface for the metal foil; a second, substantially conical part, which protrudes relative to the rear surface of the first part; and a substantially conical cavity, the cavity: having a bottom surface defined by an inclined plane; having an opening at a base of the conical cavity, where the cavity base is surrounded by a front surface of the irradiation cell; being configured to contain the target fluid; passing through the first part to extend into the second part; and running into the front surface of the first part at an acute angle () to form in the first part the opening defined by an edge, wherein an outer surface of the second part comprises furrows extending from an area close to an apex of the second part toward a region near a base of the second part, so as to create pathways between the furrows for the passage of a non-cryogenic coolant flowing along the outer surface of the second part, and wherein the metal foil is: connected to the front surface of the irradiation cell; and configured to close the opening at the edge when the metal foil bears on the front surface of the first part.

11. The irradiation cell according to claim 10, wherein the first part further comprises a groove, which, on a side of the rear surface of the first part, surrounds an outer surface of the second part, so as to reduce a thickness of the first part at the base of the second part, the groove being configured to collect the non-cryogenic coolant flowing along the outer surface of the second part.

12. The device according to claim 1, wherein the acute angle () has a size of between 45 and 85.

13. The device according to claim 1, wherein the acute angle () has a size of between 60 and 85.

14. The device according to claim 1, wherein the cavity comprises an inlet channel disposed proximal to the base of the cavity, the inlet channel being configured to introduce the target fluid into the cavity.

15. The device according to claim 1, wherein the inclined surface comprises an output channel disposed proximal to the base of the cavity, the output channel being configured to remove the collected target fluid.

16. The device according to claim 15, wherein the output channel is angled.

17. The device according to claim 1, wherein the cooling device comprises a diffuser forming an annular channel around the irradiation cell, the annular channel being configured to circulate the non-cryogenic coolant to cool walls of the cavity.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a longitudinal cross-section of part of the device according to one embodiment of the present invention.

(2) FIG. 2 is a three-dimensional view of an irradiation cell according to one embodiment of the present invention.

(3) FIG. 3 is a longitudinal cross-section along an axis A-B of the irradiation cell of FIG. 2.

(4) FIG. 4 is a cross-section identical to that of FIG. 3, in which different dimensions of the irradiation cell of FIG. 2 are indicated.

DETAILED DESCRIPTION OF THE INVENTION

(5) The device according to the present invention is designed to be used in the context of radioisotope production, in particular through irradiation of a target fluid using an accelerated particle beam. One preferred use of the device 1 according to the present invention is the production of .sup.18F through bombardment using an accelerated proton beam 13 on .sup.18O-enriched water. Preferably, the beam 13 is substantially horizontal.

(6) FIG. 1 shows a longitudinal cross-section of part of the device 1 according to one embodiment of the present invention. The device 1 of the present invention comprises an irradiation cell 7 shown in a three-dimensional view in FIG. 2. The irradiation cell 7 comprises a cavity 3 designed to contain a target fluid, for example 180-enriched water. As indicated in FIG. 3, the cavity 3 has an upper (or top) part 19 (located above the plane A-B) and a lower (or bottom) part 20 (located below the plane A-B). During operation, the plane A-B is substantially horizontal. The cavity 3 comprises an opening at a base 23 of the cavity 3, the opening closed by a metal foil 4 transparent to the beam 13. In the context of the present invention, the expression foil transparent to the beam means that substantially all of the beam 13 can pass through the metal foil 4 without being attenuated by the metal foil 4. The metal foil 4 is preferably positioned substantially perpendicular to the axis of the particle beam 13. The metal foil 4 is characterized by an upper (or top) part and a lower (or bottom) part, as shown in FIG. 3, substantially coinciding respectively with the upper (or top) part 19 and the lower (or bottom) part 20 of the cavity 3. The metal foil 4 is kept sealably against the upper surface of the irradiation cell 7. A seal 6 is positioned between the metal foil 4 and the irradiation cell 7, so as to ensure sealing.

(7) FIG. 1 shows that the irradiation cell 7 comprises an inlet channel 2 preferably emerging in the upper part 19 of the cavity 3 and near the metal foil 4 for the introduction of the target fluid into the cavity 3, and an output channel 5 for removing target fluid, preferably beginning in the lower part 20 of the cavity 3. Preferably, the inlet 2 and outlet 5 channels are situated less than 10 mm, still more preferably less than 5 mm, still more preferably less than 3 mm, from the foil 4 such that the filling of the cavity and evacuation of the target fluid are made easier. Advantageously, the irradiation cell 7 comprised in the device 1 according to the present invention is used in a radioisotope production device comprising a loop in which a target fluid can be circulated periodically through the irradiation cell and a cooling and/or capture system for the produced radioisotope, as described in document WO 02101758. In the context of this preferred aspect, the position and the incline of the inlet channel 2 relative to the metal foil 4 are advantageously selected so as to form an additional means for cooling the metal foil 4. The selection of the position and the optimal incline of the inlet channel 2 relative to the foil 4 are well within the skills of one skilled in the art.

(8) The irradiation cell 7 can be inserted into a body 8 comprising a cooling device. The cooling device comprises a coolant inlet 9, preferably a non-cryogenic coolant. The coolant intake 9 is preferably situated along the axis A-B and oriented toward the part of the irradiation cell 7 opposite the foil 4. Preferably, the cooling device also comprises a diffuser 14 creating an annular channel 10 around the irradiation cell 7. The coolant circulating in the channel 10 must ensure that the walls of the irradiation cell 7 are cooled enough for the target fluid comprised in the cavity 3 to remain essentially in liquid form.

(9) The cavity 3 comprises, in the lower part 20 thereof, an inclined surface 15 (here a concave conical surface, since the cavity 3 is preferably substantially conical). This inclined surface 15 delimits the lower part 20 of the cavity at the bottom thereof, so as to evacuate the target fluid, which condenses in contact with the cold walls of the cavity 3 by gravity toward said metal foil 4. It intercepts the plane formed by the metal foil 4 by forming an acute angle () with that plane, so as to form an area 18 capable of receiving, by gravity, the coolant that (during operation) condenses in contact with the walls of the cavity 3 cooled by the cooling device. Preferably, the acute angle () is comprised between 30 and 89, more preferably between 45 and 85, and still more preferably between 60 and 85. The inclined surface 15 is in contact with the lower part of the metal foil 4, thereby creating the area 18 of the cavity 3 in contact with the metal foil 4 in which target fluid condensed on the walls of the cavity 3 may accumulate more quickly. FIG. 3 shows that this area 18 is in the shape of a corner, defined between the plane formed by the metal foil 4, the inclined surface 15, which intercepts the plane formed by the metal foil 4 at the edge 22, and a horizontal plane, which intercepts the inclined surface 15 and the plane formed by the metal foil 4. In that area 18, the height of the collective condensed fluid is maximal at the metal foil 4 (i.e., where the fluid is in direct contact with the metal foil 4) and decreases gradually moving away from the metal foil 4 (i.e., toward the inside of the cavity 3). The condensed target fluid in contact with the metal foil 4 in the area 18 of the cavity 3 minimizes heating of the foil and therefore heating of the seals 6, which ensures good sealing of the cavity 3 relative to the devices of the prior art. It will be seen that the corner-shaped area 18 in particular guarantees a maximal height of the liquid at the metal foil. It also reduces the risk of local overheating of the condensed fluid, owing to excellent circulation by convection of the liquid in that area. Likewise, the continuous contribution of condensed target fluid at the walls of the metal foil 4 minimizes the heating of the metal foil 4 and reduces the risk of damage thereof. Consequently, the metal foil 4 being better cooled relative to the foils of the devices of the prior art, the inner pressure in the cavity 3 decreases and it is possible to reduce the thickness of the foil, which limits energy losses of the beam 13 in the metal foil 4.

(10) According to one preferred aspect, the cavity 3 is substantially conical. The conical shape of the cavity makes it possible to maximize the cooled surface S.sub.r relative to the volume of the cavity V.sub.c. It has in fact surprisingly been discovered that if the S.sub.r/V.sub.c ratios are compared to the shapes of the cavities of the prior art with that of the present invention, it can be seen that for a given opening radius of the cavity R and depth of the cavity P (FIG. 4), this ratio is higher in the case of a cavity with a substantially conical shape. Tables 1, 2 and 3 below show this comparison.

(11) TABLE-US-00001 TABLE 1 Cylinder (Radius = 2 cm, Height = 2 cm) + Hemisphere Shape of the Hemisphere (Radius = 2 cm) cavity Cone Cylinder (BE1011263) (WO2005081263) Radius R of the 2 2 2 2 opening of the cavity (cm) Depth P of the 2 2 2 4 cavity (cm) Volume Vc of 8.4 25.1 16.7 41.9 the cavity (cm.sup.3) Area of the 17.8 37.7 25.1 50.2 cooled surface Sr (cm.sup.2) Sr/Vc (cm.sup.1) 2.12 1.5 1.5 1.2

(12) TABLE-US-00002 TABLE 2 Cylinder (Radius = 2 cm, Height = 2 cm) + Hemisphere Shape of the (Radius = 2 cm) cavity Cone (WO2005081263) Radius R of the 2 2 opening of the cavity (cm) Depth P of the 4 4 cavity (cm) Volume Vc of 16.7 41.9 the cavity (cm.sup.3) Area of the 28.1 50.2 cooled surface Sr (cm.sup.2) Sr/Vc (cm.sup.1) 1.7 1.2

(13) TABLE-US-00003 TABLE 3 Cylinder (Radius = 2 cm, Height = 2 cm) + Hemisphere Shape of the (Radius = 2 cm) cavity Cone (WO2005081263) Radius R of the 1 1 opening of the cavity (cm) Depth P of the 4 4 cavity (cm) Volume Vc of 4.2 20.9 the cavity (cm.sup.3) Area of the 12.9 25.1 cooled surface Sr (cm.sup.2) Sr/Vc (cm.sup.1) 3.1 1.2

(14) Tables 1, 2 and 3 show that for a same depth P of the cavity and a same opening radius R of the cavity, the volume of a conical irradiation cell is always smaller than the volume of an irradiation cell comprising a cylindrical part and a hemispherical part as described in document WO 2005081263. Consequently, for a same depth P of the cavity and a same opening radius R of the cavity, the area of the cooled surface per unit of volume ratio Sr/Vc for a conical irradiation cell is always larger than that of an irradiation cell as described in document WO 2005081263. Advantageously, the irradiation cell 7 for use in the device 1 according to the present invention therefore enables the irradiation of a reduced target fluid volume, while keeping the depth of the cavity 3 sufficient to prevent beam losses, and providing improved cooling.

(15) According to another preferred aspect, the irradiation cell is made from niobium, a material chosen for its chemical inertia properties and acceptable thermal properties. Niobium does not produce secondary radioisotopes whereof the half-life time exceeds 24 hours. Niobium nevertheless has the drawback of being difficult to machine, which is why in this preferred aspect, the apex of the cell is preferably rounded.

(16) One example embodiment of an irradiation cell made from niobium is shown in FIG. 4. The irradiation cell 7 is in the shape of a cone with height H and radius R. The cone is tapered by a plane parallel to the base of the cone, at height Hh1, where the cone has a radius r1. This tapered part is topped by a spherical cap with radius r and height h2 relative to the base of said disk with radius r1. Advantageously, the depth P of the cavity 3 is greater than the diameter of the opening of the cavity 3, so as to minimize the volume of target fluid, while preserving a sufficient depth to irradiate the target fluid effectively.

(17) According to another preferred aspect, the radius R of the opening of the cavity is comprised between 2 mm and 20 mm, more preferably between 5 mm and 15 mm, and the depth of the cavity is preferably comprised between 1 and 10 cm, more preferably between 1 cm and 5 cm.

(18) According to another preferred aspect, the height h2 of the spherical cap is less than 1 cm.

(19) An irradiation cell 7 according to one preferred aspect is shown in FIGS. 2, 3 and 4. The irradiation cell 7 comprises: a first part 16 comprising a front surface, which forms a bearing surface for the metal foil 4, and a rear surface; and a second, substantially conical part 17, that protrudes relative to said rear surface of said first part 16.

(20) The conical cavity 3 passes through the first part 16 to extend into the second part 17, and forms, in the front surface of the first part 16, an opening delimited by the edge 22, with a circular shape, such that said metal foil 4 closes the opening at the edge 22 when it bears on the front surface of the first part 16.

(21) According to another preferred aspect of the present invention, the outer surface of the second part 17 of the irradiation cell 7 comprises linear furrows 12, each of said furrows 12 preferably extending from a region/area close to the apex of the second substantially conical part 17 toward a region near the base of the second substantially conical part 17, so as to create pathways between them making it possible to accelerate the passage of the coolant 9 and therefore to improve cooling. The addition of the furrows 12 also causes an increase in the outer surface area of the cone and therefore the heat exchange surface area.

(22) According to still another preferred aspect, the first part 16 of the irradiation cell 7 also comprises an annular groove 11 surrounding the second part 17, at the base of the second, substantially conical part 17, locally reducing the thickness of the first part 16 of the irradiation cell 7. FIG. 1 shows that this groove 11 is in direct communication with the annular channel 10 defined by the diffuser 14 around the outer surface of the first part 16. This makes it possible to evacuate the coolant in the annular channel 10 created by the diffuser 14. The circulation of a coolant in the annular groove 11 and the locally reduced thickness in the first part 16 of the irradiation cell 7 at the annular groove 11 enables improved cooling of the foil 4 closing the cavity 3.