JP6037658B2 - Neutron generator - Google Patents

Description

  The present invention relates to a neutron generator for generating neutrons by irradiating a liquid metal with a proton beam.

  Currently, boron neutron capture therapy (BNCT) is attracting attention as a technology that can selectively kill cancer cells. In BNCT, a liquid metal such as liquid lithium is used as a target, and a neutron generator that generates neutrons by irradiating the target with protons is used. As such a neutron generator, the technique described in Patent Document 1 is known.

  FIG. 6 is a block diagram showing an example of a conventional neutron generator. This neutron generator 500 has a configuration in which a beam duct 503 is connected to a reaction tank 502 in which liquid lithium is passed. A curved back wall 501 is formed inside the reaction tank 502, and liquid lithium is ejected from a nozzle 511 provided on the upper portion of the reaction tank 502, and the target T of the liquid lithium film is formed on the back wall 501 by the centrifugal force. In the beam duct 503, three orifice plates 507 having an incident hole 508 having a predetermined diameter are provided. The vacuum pump 505 is provided for each space 531 partitioned by the orifice plate 507.

  According to such a configuration, the degree of vacuum in the reaction tank 502 becomes lower than that in the beam duct 503 due to the exhaust resistance by the orifice plate 507, so that the boiling point temperature of the target T rises. As a result, the degree of vacuum in the reaction vessel 502 can be prevented from becoming high, so that liquid lithium is less likely to boil, and evaporated liquid lithium can be prevented from flowing into the accelerator through the beam duct 503.

JP 7-249498 A

However, in the conventional neutron generator 500, when the diameter of the proton beam B increases, the diameter of the entrance hole 508 of the orifice plate 507 must be increased accordingly. For this reason, there is a problem that the conductance between the reaction tank 502 and the beam duct 503 cannot be reduced, and the vacuum degree of the reaction tank 502 and the beam duct 503 cannot be set well. The present invention has been made to solve such problems.

  A neutron generator according to a first invention is a neutron generator for generating a neutron by a nuclear reaction by irradiating a proton beam to a liquid metal target, and divides a region where the liquid metal target and the proton beam react A reaction vessel to be formed, a beam duct connected to and transported to the reaction vessel to guide the proton beam into the reaction vessel, an electromagnet for focusing the proton beam provided around the beam duct, a beam duct and a reaction vessel, An orifice plate provided with an entrance hole having a size smaller than the diameter of the proton beam which has been provided and transported and which can pass through the focusing portion focused by the electromagnet, and the reaction vessel and beam duct And a vacuum pump connected to.

  In the neutron generator of the present invention, a proton beam is focused by an electromagnet, and the reaction vessel and the beam duct are partitioned by an orifice plate having an incident hole having a diameter through which the focusing portion can pass. The conductance can be reduced. For this reason, the freedom degree of the setting of the vacuum degree of a reaction tank and a beam duct can be raised. The incident hole includes not only the hole but also a tubular pipe. The diameter of the incident hole is a diameter when the incident hole is circular, a short diameter when it is elliptical, a short side length when it is rectangular, and an inscribed circle when it is polygonal. Means the diameter of.

  Moreover, in the said invention, it is further preferable to connect a vacuum pump to a reaction tank or a beam duct.

  By connecting a vacuum pump to the beam duct, a sufficient differential pressure can be secured between the beam duct and the reaction vessel. In particular, when the vacuum pump is connected to the reaction vessel, it becomes difficult for liquid metal to adhere to the vicinity of the entrance hole of the orifice plate.

  In the above invention, it is preferable that a plurality of the orifice plates are further provided in the beam duct, and the vacuum pump is provided in a part or all of the space defined by the orifice plates.

  By forming a space by the orifice plate between the reaction tank and the beam duct, it becomes possible to set the degree of vacuum more freely between the reaction tank and the beam duct.

  In the above invention, it is preferable that the diameter of the entrance hole of the orifice plate is set in accordance with the shape of the converging part that is converged by the electromagnet.

  Matching with the shape of the converging part means that the converging part of the proton beam has a conical shape that spreads to the left and right by the electromagnet. is there. Thereby, only the dimension necessary for the passage of the proton beam can be used as the orifice, so that the conductance between the reaction vessel and the beam duct can be further reduced, and the degree of freedom in setting the degree of vacuum is improved.

It is a block diagram which shows the neutron generator concerning Embodiment 1 of this invention. It is explanatory drawing which shows the modification of the neutron generator shown in FIG. It is explanatory drawing which shows the modification of the neutron generator shown in FIG. It is a block diagram which shows the neutron generator which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows the modification of the neutron generator shown in FIG. It is a block diagram which shows an example of the conventional neutron generator.

(Embodiment 1)
FIG. 1 is a block diagram showing a neutron generator according to Embodiment 1 of the present invention. The neutron generator 100 includes a reaction tank 2 in which a target forming unit 1 is provided and a region in which a liquid metal target T and a proton beam B react with each other, and is connected to the reaction tank 2 and an accelerator (illustrated). A beam duct 3 for guiding the proton beam B transported from the reaction tank 2 to the reaction tank 2, an electromagnet 4 provided around the beam duct 3, and vacuum pumps 5 and 6 provided in the beam duct 3 and the reaction tank 2. Have.

  The target forming unit 1 includes a nozzle 11 that ejects a liquid metal in a plane so as to cross the irradiation region of the proton beam B, and a receiving unit 12 that includes a diffuser that receives the ejected liquid metal. The target forming unit 1 is connected to a quench tank, an electromagnetic pump, and a heat exchanger via a pipe and constitutes a liquid metal loop as a whole (all not shown). The liquid metal is, for example, liquid lithium. Note that the target forming unit 1 may have a structure in which liquid lithium flows on a curved back wall as shown in FIG. 4 (not shown).

  At the end 3a of the beam duct 3, an orifice plate 7 provided with a circular incident hole 8 is provided. The orifice plate 7 is made of ferritic steel or stainless steel. The diameter of the entrance hole 8 of the orifice plate 7 is set slightly larger than the minimum diameter of the converging part Bs when converging the proton beam B (the diameter of the part where the proton beam is most constricted). Further, the conductance between the reaction vessel 2 and the beam duct 3 can be further reduced by increasing the thickness of the orifice plate 7.

  The electromagnet 4 is composed of, for example, a quadrupole electromagnet. As means for bending the proton beam B, a known object can be used in addition to the electromagnet 4. As the vacuum pumps 5 and 6, a turbo molecular pump, an ion pump or the like is used.

  In this neutron generator 100, the proton beam B is focused by the electromagnet 4 to form a focusing portion Bs in the proton beam B. The converging portion Bs is adjusted so that the position of the incident hole 8 of the orifice plate 7 has a minimum diameter. The proton beam B that has passed through the incident hole 8 travels in a conical shape spreading toward the end, and is irradiated onto the liquid metal target T, and neutrons are generated behind the liquid metal target T. The flux amount of the proton beam B when irradiating the liquid metal target T is suppressed to such an extent that the liquid metal does not evaporate. For this reason, the distance between the incident hole 8 and the electromagnet 4 and the distance between the incident hole 8 and the liquid metal target T are substantially the same so that the portion near the minimum diameter of the converging part Bs is not irradiated onto the liquid metal target T. Is preferable.

  The inside of the reaction vessel 2 and the beam duct 3 is differentially evacuated until a predetermined degree of vacuum is obtained by vacuum pumps 5 and 6 connected thereto. In this neutron generator 100, the proton beam B is focused and passed through the entrance hole 8 of the orifice plate 7. Therefore, the entrance hole 8 has a diameter smaller than the diameter of the unfocused proton beam B transported from the accelerator. can do. For this reason, the conductance between the reaction tank 2 and the beam duct 3 is reduced, and a sufficient differential pressure can be secured between the reaction tank 2 and the beam duct 3.

The boiling point temperature of the liquid metal can be increased by setting the pressure in the reaction tank 2 high by differential exhaust. For example, the pressure in the reaction vessel 2 can be set to about 1 × 10 ⁴ Torr, and the pressure in the beam duct 3 can be set to about 1 × 10 ⁶ Torr. For this reason, evaporation of the liquid metal due to irradiation with the proton beam B is suppressed. Further, even if the liquid metal evaporates, the entrance hole 8 of the orifice plate 7 is sufficiently small so that the liquid metal vapor does not easily flow into the beam duct 3. The shape of the entrance hole 8 of the orifice plate 7 is not limited to a circle, and may be an ellipse, for example. In the case of an ellipse, the minor axis is set to be slightly larger than the minimum diameter of the converging part Bs. In the case of a rectangle, the short side length (referred to as a diameter for convenience) is set to be slightly larger than the minimum diameter of the converging part Bs. In the case of a triangle of five or more polygons, the diameter of the inscribed circle is set to be slightly larger than the minimum diameter of the converging part Bs. Further, by providing the vacuum pump 6 separately from the vacuum pump 5, it is possible to prevent the evaporated liquid metal from adhering around the entrance hole 8.

  As shown in FIG. 2A, the conductance can be further reduced by providing a straight tubular orifice pipe 9 in the incident hole 8. The length and inner diameter of the orifice pipe 9 are determined based on the shape of the converging part Bs of the proton beam B formed by the electromagnet 4. Further, as shown in FIG. 2B, the orifice pipe 10 may be a cylindrical body having both sides of a trumpet shape in accordance with the shape of the converging part Bs of the proton beam B. In this way, conductance can be further reduced.

  As another example of the neutron generator according to the first embodiment, a cooling unit 50 may be provided around the beam duct 3 as shown in FIG. In other words, the cooling means 50 is provided at least between the accelerator of the beam duct 3 and the orifice plate 7. The cooling means 50 may be configured, for example, such that a tube is wound around the outer peripheral surface of the beam duct 3 and cooling water is passed through the inside, or a cooling device having a simple structure such as a Peltier element.

  Since the evaporated liquid metal tends to be adsorbed on the surface as the temperature is lower, the cooling means 50 is provided in the beam duct 3 and is actively adsorbed on the inner surface of the beam duct 3. Thereby, it can prevent that the liquid metal which evaporated near the entrance hole 8 adheres, and a diameter becomes small. The vapor of the liquid metal that has evaporated and passed through the incident hole 8 is adsorbed by the beam duct 3 cooled by the cooling means 50. Thereby, it is possible to prevent the evaporated liquid metal from moving to the accelerator side.

  Further, heating means such as a heater for heating the orifice plate 7 may be provided on the orifice plate 7 to prevent the liquid metal from adhering (not shown). Furthermore, a temperature difference may be provided between the orifice plate 7 and the beam duct 3 based on design conditions so that the temperature of the beam duct 3 is lower than that of the orifice plate 7.

(Embodiment 2)
FIG. 4 is a block diagram showing a neutron generator according to Embodiment 2 of the present invention. The neutron generator 200 has substantially the same configuration as that of the first embodiment, but a plurality of orifice plates 71, 72, 73 are provided in the beam duct 3, and spaces 31, 32 partitioned by the orifice plates 71, 72, 73 are provided. The difference is that vacuum pumps 51, 52, 53 are provided in the beam duct 3, respectively.

  The incident holes 81, 82, 83 of the orifice plates 71, 72, 73 are set according to the shape of both ends of the converging part Bs when the proton beam B is converged. Since the entrance hole 82 of the central orifice plate 72 is located in a portion where the minimum beam diameter of the converging portion Bs is formed, it is set slightly larger than the beam diameter. The incident holes 81 and 83 of the left and right orifice plates 71 and 73 have a diameter through which the proton beam B can pass at the position where the orifice plates 71 and 73 are installed. That is, since the diameter of the entrance hole 82 of the central orifice plate 72 is smaller than the diameter of the entrance holes 81 and 83 of the left and right orifice plates 71 and 73, the conductance between the reaction tank 2 and the beam duct 3 is further reduced. .

  The vacuum pumps 51, 52, and 53 are the reaction tank 2, the first space 31 defined by the first orifice plate 71 and the second orifice plate 72, and the second space 32 defined by the second orifice plate 72 and the third orifice plate 73. , And the beam duct 3, respectively.

  In this neutron generator, a pressure difference is generated in stages between the reaction tank 2, the first space 31, the second space 32, and the beam duct 3, and the degree of vacuum in the reaction tank 2 is set to the degree of vacuum in the beam duct 3. Can be lower. Further, even if the liquid metal evaporates, the vapor flowing into the beam duct 3 by the first space 31 and the second space 32 can be suppressed. For this reason, it is possible to sufficiently prevent the liquid metal vapor from flowing into the accelerator.

  One of the left and right orifice plates 71 and 73 may be omitted (not shown). In that case, one space is formed between the beam duct 3 and the reaction vessel 2. Further, any one of the vacuum pumps 51, 52, 53, 6 may be omitted. For example, one of the vacuum pumps 51 and 52 provided in all of the first space 31 and the second space 32 may be omitted, and the vacuum pump may be provided only in a part of the spaces.

  In the neutron generator 200 according to the second embodiment, the cooling unit 60 may be provided outside the beam duct 3 and around the first space 31. As a result, the evaporated liquid metal that has entered the first space 31 can be effectively trapped in the first space 31. Since the first space 31 is partitioned by the orifice plates 71 and 72, it is difficult for the metal vapor to escape, and the inner surface of the beam duct 3 in the first space 31 is cooled, so that the evaporated metal is easily adsorbed on the inner surface. This makes it difficult for the liquid metal vapor to enter the beam duct 3 through the first space 31. The cooling means 60 may be configured, for example, by winding a tube around the outer peripheral surface of the beam duct 3 and allowing cooling water to pass therethrough, or a cooling device having a simple structure such as a Peltier element. The cooling means 60 may be provided outside the beam duct 3 and around the second space 32 (not shown). In this case, the liquid metal vapor is trapped in the second space 32. Furthermore, the cooling means 60 may be provided over the entire outer circumference of the beam duct 3 (not shown).

(Embodiment 3)
FIG. 5 is a configuration diagram showing a modification of the neutron generator according to the second embodiment. This neutron generator 250 is provided with a gas introduction duct 65 in the first space 31 of the neutron generator 200 according to the second embodiment, and gas that inhibits the movement of Li molecules such as helium and argon from the gas generator 66. This is a configuration to be introduced. The pressure of the first space 31 increases due to gas scattering, and liquid metal molecules can be prevented from entering from the orifice plate 71. This makes it difficult for the metal vapor to move to the electromagnet 4 side of the beam duct 3. Further, the gas generating means 66 can be provided in the second space 32.

  If the gas introducing means (65, 66) and the cooling means 60 are used in combination, the liquid metal can be more effectively prevented from adhering to the upstream of the beam duct 3 or the accelerator.

DESCRIPTION OF SYMBOLS 100 Neutron generator 1 Target formation part 2 Reaction tank 3 Beam duct 4 Electromagnets 5 and 6 Vacuum pump 7 Orifice plate 8 Entrance hole T Target B Proton beam Bs Focusing part

Claims (6)

A neutron generator for generating a neutron by irradiating a liquid metal target with a proton beam transported from an accelerator ,
A reaction vessel that defines a region where the liquid metal target and the proton beam react; and
A beam duct connected to the reaction vessel and guiding the proton beam into the reaction vessel;
An electromagnet for focusing the proton beam provided around the beam duct;
An orifice plate provided between the beam duct and the reaction vessel and provided with an entrance hole having a diameter smaller than the diameter of the proton beam before focusing and having a size through which the focusing portion focused by the electromagnet can pass;
A cooling means disposed between the orifice plate and the accelerator and disposed on an outer peripheral surface of the beam duct for cooling the beam duct;
A neutron generator characterized by comprising: Furthermore, the neutron generator of Claim 1 which connected the vacuum pump to the said reaction tank or beam duct. The neutron generator according to claim 2, further comprising a plurality of orifice plates provided in a beam duct, wherein the vacuum pump is provided in a part or all of a space defined by the orifice plates. 4. The neutron generator according to claim 3, wherein the diameter of the entrance hole of the orifice plate is set in accordance with the shape of the converging part focused by the electromagnet. The neutron generator according to claim 3 or 4 , further comprising gas introduction means for introducing gas into a space partitioned by the orifice plate. The neutron generator according to claim 1, further comprising a heating unit that heats the orifice plate.