JP2006196353A - Accelerator neutron source and boron neutron acquisition treatment system using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an accelerator neutron source capable of generating neutron stably by performing cooling of a metal target excellently and a boron neutron acquisition treatment system using this. <P>SOLUTION: The accelerator neutron source 6 generates neutrons using a proton beam 10 accelerated by a linear accelerator such as an RFQ linac 2 and a drift tube linac 3. The accelerator neutron source has a metal target 11 of a plate shape on which the proton beam 10 is irradiated and a cooling device 15 which has cooling water passages 12a-12e inside and on one side surface 13 of which the metal target 11 is jointed and in which the one side surface 13 has an area larger than that of the jointing part 14 with the metal target 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an accelerator neutron source that generates neutrons by irradiating a metal target with a charged particle beam accelerated by an accelerator, and a boron neutron capture therapy system using the accelerator neutron source.

Boron neutron capture therapy differs from radiotherapy such as X-rays and charged particle beams in that the nuclear reaction ( ¹⁰ B (n) between boron ( ¹⁰ B) that has been administered in advance and localized inside the tumor and neutrons irradiated from the outside. , α) ⁷ Li) is a treatment method that uses α rays and lithium nuclei ( ⁷ Li) to kill tumor cells. Since the range of α rays and lithium nuclei ( ⁷ Li) is about one cell, the tumor can be killed without damaging normal cells. As a system for performing such boron neutron capture therapy, there is a system that uses neutrons generated from a nuclear reactor (for example, see Non-Patent Document 1). However, it is difficult to establish a new nuclear reactor, and even when an existing nuclear reactor is used, the use of the nuclear reactor is subject to various regulations, which has a problem that it imposes a heavy burden on doctors who perform treatment. .

Thus, an inexpensive and simple accelerator system for boron capture therapy using an accelerator is desired. In this accelerator system, neutrons are generated by irradiating a metal target with a charged particle beam accelerated by the accelerator. As an accelerator for boron capture therapy, conventionally, an acceleration energy of protons using lithium ( ⁷ Li) as a target and a ⁷ Li (p, n) ⁷ Be reaction is about 2.5 MeV or less, or tungsten or Protons whose accelerating energy is 50 MeV or higher using tantalum or the like as a target and utilizing these nuclear fragmentation reactions have been proposed (for example, see Non-Patent Document 2). However, the former accelerator using lithium has a problem that it is difficult to withstand the heat load of accelerated protons because the melting point of ⁷ Li is as low as 179 ° C. Further, in the latter accelerator using tungsten, tantalum, etc., high energy neutrons are generated by the spallation reaction, and a large amount of moderators and shielding materials are required for the deceleration or shielding. However, there was a problem that it would be large and expensive.

From this point of view, in recent years, an accelerator system for generating neutrons by the nuclear reaction ⁹ Be (p, n) ⁹ B using beryllium ( ⁹ Be: melting point 1287 ° C.), which is a high melting point material, is used as a target. Has been advocated.

The Institute of Electrical Engineers of Japan, “Advanced Radiation Medical Technology and Measurement”, first edition, Corona Co., Ltd., November 15, 2001, p. 40-57 Shin Inoue, “Accelerator for Neutron Capture Medical”, [online], September 18, 1996, [December 5, 2004], Internet <URL: http://www.rada.or.jp:8180/member /detail/040016.html>

However, there are the following problems in the above-described prior art.
That is, when using the accelerator system targeting beryllium and applying neutrons generated by the nuclear reaction ⁹ Be (p, n) ⁹ B between protons and beryllium to boron neutron capture therapy, the necessary incident proton beam Is estimated to be as large as about 30 kW. At this time, since the proton beam has a diameter of 50 to 60 mm at most, the beam output density is about 10 MW / m ² . Thus, when the heat load of the target reaches 10 MW / m ² , the cooling water itself boils immediately with a simple heat sink using ordinary cooling water, making it difficult to remove heat. As a result, there has been a problem that neutrons cannot be generated stably.

  The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide an accelerator neutron source capable of stably generating neutrons and a boron neutron capture therapy system using the same. is there.

  (1) In order to achieve the above object, the first invention of the present application is a plate-like metal target irradiated with the charged particle beam in an accelerator neutron source that generates neutrons using a charged particle beam accelerated by an accelerator. And a cooling device having a cooling water flow path therein, wherein the metal target is bonded to one side surface, and the one side surface has an area larger than an area of a joint portion with the metal target. It is characterized by that.

  In the accelerator neutron source of this embodiment, neutrons are generated by irradiating a plate-shaped metal target with a charged particle beam accelerated by the accelerator. This metal target is cooled by a cooling device having a cooling water channel therein.

Here, for example, when proton is used as a charged particle beam and beryllium ( ⁹ Be) is used as a metal target, for example, it is necessary to generate neutrons by nuclear reaction ⁹ Be (p, n) ⁹ B between proton and beryllium. It is estimated that the output of a large incident proton beam will be as large as about 30 kW. At this time, since the diameter of the proton beam is normally 50 to 60 mm at most, the beam output density is about 10 MW / m ² . Thus, when the heat load of the metal target reaches 10 MW / m ² , the cooling water itself boils immediately with a simple heat sink using ordinary cooling water, making it difficult to remove heat. As a result, there has been a problem that neutrons cannot be generated stably.

On the other hand, in this invention, it has a cooling water flow path in the inside, a metal target is joined to the surface of one side, and the surface of the one side has an area larger than the area of a junction part with a metal target. The metal target is cooled using a cooling device. By adopting such a structure, the surface area (that is, the effective heat transfer area) on the side facing the metal target in the surface area of the cooling water flow path in the cooling apparatus is joined to the surface on one side of the cooling apparatus (that is, the metal target and the joint). It is possible to make it approximately equal to or more than the area of the surface to be provided). As a result, the effective heat transfer area can be significantly increased compared to the conventional case, and heat can be removed well even when the heat load of the metal target is 10 MW / m ² as described above. . As a result, neutrons can be generated stably.

  (2) The second invention of the present application is the above-described first invention, wherein the cooling water passage has a surface area on the side facing the metal target of the surface area substantially equal to an area of one surface of the cooling device, or It is provided in the said cooling device so that it may become larger.

  (3) According to a third invention of the present application, in the first or second invention, the cooling water flow path is provided in the cooling device so that a minimum distance from the metal target is about the thickness of the metal target. It is characterized by.

  Generally, the cooling efficiency is improved as the distance between the metal target and the cooling water flow path is smaller. However, when the metal target is directly cooled with cooling water at a distance of zero, there is a concern about the corrosion of the metal target due to the cooling water, and the strength to support the metal target is also necessary. A certain amount of thickness (distance) is required between the road.

  In the present invention, the cooling water flow path is provided in the cooling device so that the minimum distance from the metal target is about the thickness of the metal target. This makes it possible to properly balance the above-described support strength and cooling efficiency, prevent corrosion due to cooling water and ensure support strength, and maintain good cooling efficiency. It is.

  (4) In the fourth invention of the present application, in any one of the first to third inventions, the metal target has a thickness substantially equal to or slightly larger than a range of the charged particle beam in the metal target. It is characterized by having.

  If the thickness of the metal target is too large, the accelerator neutron source will be increased in size and the cooling efficiency will be reduced. However, for example, when the thickness of the metal target is thinner than the range of the charged particle beam in the metal target, a part of the charged particle beam irradiated to the metal target passes through the metal target without being used for the nuclear reaction. As a result, the amount of neutron generation decreases.

  In the present invention, the thickness of the metal target is approximately equal to or slightly larger than the range of the charged particle beam in the metal target. Thereby, while suppressing the enlargement of an accelerator neutron source and the fall of cooling efficiency to the minimum, almost all of the charged particle beam irradiated to the metal target can be used for a nuclear reaction, and a neutron can be taken out effectively.

  (5) According to a fifth invention of the present application, in any one of the first to fourth inventions, the metal target and the cooling device are joined by high-temperature isotropic pressure joining or high-temperature brazing joining. And

  By adopting such a joining method, it is possible to sufficiently cope with a high heat load. In particular, high-temperature isotropic pressure bonding has an effect that not only heat resistance but also uniformity of the bonding surface is superior to that of high-temperature brazing, and bubbles or the like are hardly generated on the bonding surface.

(6) The sixth invention of the present application is characterized in that, in any one of the first to fifth inventions, the charged particle beam is a proton beam, and the metal target is beryllium ( ⁹ Be).

  (7) In order to achieve the above object, the seventh invention of the present application is an accelerator neutron source for generating neutrons by irradiating a metal target with a charged particle beam accelerated by an accelerator, wherein the metal target is the charged particle. The surface on which the beam is irradiated has an inclined surface inclined with respect to the traveling direction of the charged particle beam, and a cooling water flow path is provided inside.

  In the present invention, a metal target having an inclined surface inclined with respect to the traveling direction of the charged particle beam on the surface irradiated with the charged particle beam and having a cooling water channel inside is used. Thus, the effective irradiation area can be increased by using a metal target having an inclined surface inclined with respect to the traveling direction of the charged particle beam on the irradiation side. Thereby, since an effective heat load can be reduced, the heat of the metal target can be favorably removed by the cooling water flow path provided inside. As a result, neutrons can be generated stably.

  (8) The eighth invention of the present application is characterized in that, in the seventh invention, the metal target can be divided into a plurality of pieces.

  (9) In order to achieve the above object, the ninth invention of the present application is accelerated by a charged particle source for generating charged particles, an accelerator for accelerating the charged particles generated by the charged particle source, and the accelerator. A beam transport system that transports a charged particle beam, and an accelerator neutron source according to any one of claims 1 to 8 that generates neutrons using the charged particle beam transported by the beam transport system. It is characterized by that.

  In the boron neutron capture therapy system of the present invention, as described in the above (1) to (8), an accelerator neutron source that can stably generate neutrons is provided, and as a result, stable treatment is performed for a long time. Is possible.

  According to the present invention, heat removal from a metal target can be performed satisfactorily and neutrons can be generated stably.

  Hereinafter, an embodiment of an accelerator neutron source of the present invention and a boron neutron capture therapy system using the same will be described with reference to the drawings.

  FIG. 1 is a diagram showing an overall schematic structure of the boron neutron capture therapy system of the present embodiment.

In FIG. 1, protons (charged particles) generated by an ion source (charged particle source) 1 are sequentially accelerated by a linear accelerator such as an RFQ linac (accelerator) 2 or a drift tube linac (accelerator) 3. Thereby, the proton beam 10 (see FIG. 2 to be described later) accelerated to high energy of MeV class or higher passes through a beam transport system such as a beam adjuster 4 composed of various magnetic field coils, and then the accelerator neutron source in the target system 5 6 (refer to FIG. 2 to be described later) is incident on a metal target (here, beryllium ( ⁹ Be)) 11 (refer to FIG. 2 to be described later), and a nuclear reaction between proton and beryllium ⁹ Be (p, n) ⁹ B To generate fast neutrons. The generated fast neutrons are further decelerated in the target system 5 by a moderator (not shown) to generate epithermal neutrons or thermal neutrons necessary for treatment, and the affected area of the patient 8 on the bed 7 (for example, in the head brain) Tumor). A shield structure (not shown) is provided around the accelerators 2 and 3, the target system 5, the patient 8, and the like in consideration of the respective levels.

  FIG. 2 is a perspective view showing the entire structure of the accelerator neutron source 6 provided in the target system 5.

  In FIG. 2, an accelerator neutron source 6 includes a plate-shaped metal target 11 irradiated with a proton beam 10 generated by the ion source 1 and accelerated by a linear accelerator such as the RFQ linac 2 and the drift tube linac 3, and a plurality of A heat sink (cooling device) 15 having (in this embodiment, five) cooling water flow paths 12a to 12e therein and the metal target 11 joined to one side surface (upper surface in FIG. 2) 13 And.

The metal target 11 is made of beryllium ( ⁹ Be) as described above, and its plate thickness Dt is approximately equal to or slightly larger than the range of the protons irradiated in the metal target 11. For example, since the range of 11 MeV protons in beryllium is 0.94 mm, the thickness of the metal target 11 in this case may be 1 mm to 2 mm.

  The heat sink 15 bonded to the back surface of the metal target 11 (the surface opposite to the irradiated surface, the lower surface in FIG. 2) is made of a metal (for example, copper) having excellent thermal conductivity, and is a block. It has a shape (other shapes may be used). In the heat sink 15, as described above, five cooling water flow paths 12a, 12b,... 12e are formed. In each of the cooling water passages 12a to 12e, cooling water having a necessary flow rate is forcibly circulated by a cooling system auxiliary machine including a forced circulation pump, a cooler (chiller), a flow rate adjusting valve, a flow meter and the like (not shown). . In addition, the flow direction of this cooling water is a parallel direction as shown in FIG. Further, the joint 14 between the metal target 11 and the heat sink 15 is formed by high-temperature isostatic pressing or high-temperature brazing.

  Here, a feature of the present embodiment is that the one surface 13 of the cooling device 15 is configured to have an area larger than the area of the joint 14 with the metal target 11. That is, it is configured to satisfy the following formula (1).

Sh = k1 · St (k1> 1) (1)
Here, Sh is the area of the surface 13 on one side of the cooling device 15, St is the area of the joint 14, and k1 is a magnification constant. The value of the magnification constant k1 is preferably 2-4.

  As a second feature, of the surface areas (that is, heat transferable area) of the cooling water flow paths 12a, 12b,... 12e in the heat sink 15, the surface area Sw (on the side facing the metal target 11 (in other words, the heat source)) Hereinafter, it is referred to as an effective heat transfer area Sw. In the case of the structure as in the present embodiment, it is usually about 40 to 60% of the heat transferable area), but the area Sh of the surface 13 on one side of the cooling device 15. It can be mentioned that it is configured to be substantially equal to or larger than. That is, it is configured to satisfy the following expression (2).

Sw = k2 · Sh (k2 = 1 to 1.2) (2)
In addition, although k2 is a magnification constant, the effective heat transfer area Sw is the cooling water flow paths 12a, 12b,... When the cooling water flow paths 12a, 12b,. Since it can be regarded as about 1/2 of the surface area of 12e (that is, the heat transferable area), about 1 to 1.2 can be expected even if the gap between the cooling water flow paths is taken into consideration.

  The third feature is that the minimum distance Ltw between the metal target 11 and the cooling water flow paths 12a, 12b,... 12e in the cooling device 15 is set to about the target plate thickness Dt.

  In the present embodiment configured as described above, the following effects can be obtained. Hereinafter, each item will be described.

(I) Effect of improving heat removal function of target That is, in the present embodiment, as described above, compared with the beam irradiation area of the metal target 11 serving as a heat source (equal to the area St of the bonding portion 14), The area Sh of the surface 13 is sufficiently large, and the effective heat transfer area Sw of the cooling water flow paths 12a, 12b,... 12e in the heat sink 15 is almost as large as the area Sh of the surface 13 on one side of the heat sink 15. Therefore, the effective heat transfer area Sw of the cooling water flow paths 12a, 12b,... 12e can be increased by an order of magnitude as compared with that conventionally considered. As a result, the nucleate boiling state in which bubbles are generated discretely on the surfaces (heat transfer surfaces) of the cooling water flow paths 12a, 12b,... 12e can be stably maintained, and the heat transfer coefficient can be increased. Thereby, even if the heat load of the metal target 11 is large, it is possible to remove heat satisfactorily, and as a result, neutrons can be generated stably.

The improvement effect of the above heat removal function will be specifically verified below.
Heat input Pe (kW) in forced convection cooling with cooling water, effective heat transfer area Sw (m ² ) of cooling water, temperature Tw (K) at the cooling water interface, cooling water average temperature Tc (K), cooling water The relationship with the heat transfer coefficient α (kW / m ² K) is given by the following equation (3).

Pe = α · Sw · (Tw−Tc) (3)
It is known that the heat transfer coefficient α increases in a form proportional to the 0.8th power of the cooling water flow velocity v (m / s) in a turbulent flow region where the flow velocity is sufficiently large (Dittus-Boelter equation). ).

FIG. 3 shows the calculation result based on the above equation. FIG. 3 shows that α = 27 kW / m ² K can be obtained at a cooling water flow rate of 5 m / s in, for example, a cooling water passage having a diameter of 1 cm. Here, when Pe = 30 kW, as a temperature condition in which the cooling water in the cooling water flow paths 12a, 12b,... 12e does not undergo film boiling (a boiling state in which the heat transfer surface and the cooling water are not in direct contact with each other). Assuming that ΔT = Tw−Tc <50K, it is understood from the above formula (3) that Sw> 220 cm ² and the effective heat transfer area Sw should be about 220 cm ² .

That is, according to the present embodiment, the area Sh of the surface 13 on one side of the cooling device 15 is set to about 220 cm ² ≈15 cm × 15 cm, and the effective heat transfer area Sw of the cooling water flow paths 12a, 12b,. ^By setting it to about ² or more, heat removal can be performed satisfactorily even in a state where the heat load of the metal target 11 is 10 MW / m ² as described above.

(Ii) Effect of improving generation efficiency of neutrons The metal target 11 is preferably as thin as possible because it leads to an increase in the size of the accelerator neutron source 6 when the thickness Dt is too large and the cooling efficiency also decreases. However, for example, when the thickness Dt of the metal target 11 is thinner than the range of the proton beam in the metal target 11, a part of the proton beam irradiated to the metal target 11 is not used for the nuclear reaction, and the metal target is used. 11, the amount of neutron generation decreases.

  In the present embodiment, as described above, the thickness Dt of the metal target 11 is set to be approximately equal to or slightly larger than the proton range. This makes it possible to effectively extract neutrons by using almost all of the proton beam irradiated to the metal target 11 for the nuclear reaction while minimizing the increase in size and cooling efficiency of the accelerator neutron source 6 described above. The effect that you can do it.

(Iii) Effect of preventing corrosion of metal target, securing support strength, and improving cooling efficiency Generally, the cooling efficiency is improved as the distance between the metal target 11 and the cooling water channel 12 is smaller. However, in the case of a structure in which the distance is set to zero and the metal target 11 is directly cooled with cooling water, there is a concern that the metal target 11 is corroded by the cooling water. Moreover, since the strength for supporting the metal target 11 is also necessary, a certain amount of thickness (distance) is required between the metal target 11 and the cooling water channel 12.

In the present embodiment, as described above, the minimum distance Ltw between the cooling water flow paths 12a, 12b,... 12e and the metal target 11 is configured to be about the thickness Dt of the metal target 11. Thereby, it is possible to appropriately balance the above-described support strength and cooling efficiency, prevent the metal target 11 from being corroded by the cooling water, and ensure the support strength of the metal target 11, and then the cooling efficiency. Can be maintained well. As a result, the surface temperature and the backside temperature of the metal target 11 (i.e. the temperature of the junction 14), melting point ⁽⁹ Be melting point: 1287 ° C.) of the metal target 11 can be suppressed sufficiently lower than that.

(Iv) Effect by Bonding Method In this embodiment, as described above, the metal target 11 and the surface 13 on one side of the cooling device 15 are bonded by high-temperature isotropic pressure bonding or high-temperature brazing bonding. These bonding methods have a high heat resistance temperature (high temperature isotropic pressure bonding has a heat resistance temperature of about 800 ° C., and high temperature brazing bonding has a heat resistance temperature of about 500 ° C.), and can sufficiently cope with a high heat load. In particular, when high-temperature isotropic pressure bonding is used, compared to high-temperature brazing, not only heat resistance but also uniformity of the bonding surface is obtained, and there is an effect that bubbles and the like are hardly generated on the bonding surface.

(V) Treatment stability improvement effect As a result of obtaining the effects described in (i) to (iv) above, according to the boron neutron capture therapy system of the present embodiment, stable required neutrons can be obtained over a long period of time. Can occur and a stable treatment can be carried out over a long period of time.

  In addition to the above, the above embodiment can be further modified in various ways without departing from the scope of the gist and technical idea. Hereinafter, such modifications will be sequentially described.

(1) Structure in which the flow of cooling water is in series FIG. 4 is a top view showing the overall structure of the accelerator neutron source 6A in the present modification. As shown in FIG. 4, in the above embodiment, the flow direction of the cooling water in the plurality of cooling water flow paths 12a, 12b,... The flow direction is in the series direction. As a result, the cooling water flow rates in all the cooling water flow paths 12a, 12b,... 12e become the same, and there is an effect that the problem of the above-described embodiment in which the flow speed may vary between the respective flow paths can be improved. .

(2) Structure in which the flow direction of the cooling water is partially in series FIG. 5 is a diagram showing only information relating to the flow of each cooling water flow path of the accelerator neutron source 6B in the present modification. As shown in FIG. 5, the cooling water flowing from the central cooling water channel inlet C1 branches to B2 and D2 at the outlet C2, and thereafter flows in series. Since the flow path after branching at C2 is a flow path with a large pressure loss including reversal of the flow direction, the flow rate balance at the time of branching is better than in the above-described embodiment in which all flow paths are parallel. Moreover, since the partial parallel flow path is formed, there is an effect that the burden on the circulation pump is smaller than that of the modification (1) in which all the flow paths are parallel.

(3) Structure in which the metal target is fitted in the recess of the cooling device Although not specifically illustrated and described in detail, in the above embodiment, the metal target 11 is joined on the surface 13 on one side of the cooling device 15. However, the present invention is not limited to this, and a recess having a shape matching the metal target 11 may be formed on the surface 13 on one side of the cooling device 15, and the metal target 11 may be fitted therein. At this time, the upper surface of the metal target 11 may protrude (or be recessed) from the one side surface 13 of the cooling device 15, or may be flush with the one side surface 13. In this case, the area Sh of the surface 13 on one side of the cooling device 15 is an area obtained by adding the area of the bottom of the recess to the area of the peripheral portion of the metal target 11. Also in this modification, the same effect as the above embodiment is obtained.

(4) Structure in which splittable metal target has cooling water flow path inside FIG. 6 is a side view showing the entire structure of accelerator neutron source 6C in the present modification. As shown in FIG. 6, in this modification, the metal target 16 is configured so as to be capable of being divided, and each of the divided small targets 16a, 16b, 16c, 16d has cooling water channels 17a, 17b, 17c, 17d. Each of the small targets 16a, 16b, 16c, and 16d has a substantially triangular prism shape with a base angle θ, and each beam irradiation surface (inclined surface) 18 has a predetermined angle (inclination) with respect to the beam incident direction. The effective irradiation area is set to be larger than the corresponding beam cross-sectional area. Each small target 16a, 16b, 16c, 16d is connected to the target support plate 19 by mechanical fastening such as bolt fastening.

  In the present modification configured as described above, the effective beam irradiation area can be set to 1 / cos θ of the corresponding beam cross-sectional area. For example, when θ = 60 degrees, the effective irradiation area is twice the beam cross-sectional area. Thus, since an effective heat load can be reduced, the heat of the metal target 16 can be well removed by the cooling water flow paths 17a, 17b, 17c, and 17d that are provided inside. As a result, neutrons can be generated stably.

It is a figure showing the whole schematic structure of one embodiment of the boron neutron capture therapy system of the present invention. It is a perspective view showing the whole structure of one embodiment of the accelerator neutron source of the present invention. It is a figure showing the relationship between the heat transfer coefficient of cooling water, and the flow velocity. It is a top view showing the whole structure of the accelerator neutron source in the modification at the time of making the flow direction of a cooling water into a serial direction. It is the figure which showed only the information regarding the flow of each cooling water flow path of the accelerator neutron source in the modification at the time of making the flow direction of cooling water partially into a serial direction. It is a side view showing the whole structure of the accelerator neutron source in the modification in which the metal target which can be divided has a cooling water channel inside.

Explanation of symbols

1 Ion source (charged particle source)
2 RFQ linac (accelerator)
3 Drift tube linac (accelerator)
4 Beam conditioner (beam transport system)
6 Accelerator Neutron Source 6A Accelerator Neutron Source 6B Accelerator Neutron Source 6C Accelerator Neutron Source 11 Metal Target 12 Cooling Water Channel 13 One Side 14 Joint 15 Heat Sink (Cooling Device)
16 Metal target 17 Cooling water flow path 18 Beam irradiation surface (inclined surface)

Claims (9)

In an accelerator neutron source that generates neutrons using a charged particle beam accelerated by an accelerator,
A plate-like metal target irradiated with the charged particle beam;
A cooling device having a cooling water flow path therein, wherein the metal target is bonded to one side surface, and the one side surface has an area larger than the area of the bonding portion with the metal target. Accelerator neutron source characterized by   The cooling water channel is provided in the cooling device so that a surface area of the surface area facing the metal target is substantially equal to or larger than an area of one surface of the cooling device. The accelerator neutron source according to claim 1.   The accelerator neutron according to claim 1 or 2, wherein the cooling water flow path is provided in the cooling device so that a minimum distance from the metal target is about the thickness of the metal target. source.   The accelerator neutron according to any one of claims 1 to 3, wherein the metal target has a thickness that is substantially equal to or slightly larger than a range of the charged particle beam in the metal target. source.   The accelerator neutron source according to any one of claims 1 to 4, wherein the metal target and the cooling device are bonded by high-temperature isotropic pressure bonding or high-temperature brazing bonding. The charged particle beam is a proton beam, accelerator neutron source according to any one of claims 1 to 5 wherein the metal target is characterized by a beryllium ⁽⁹ Be). In an accelerator neutron source that generates neutrons by irradiating a metal target with a charged particle beam accelerated by an accelerator,
The accelerator neutron source characterized in that the metal target has an inclined surface inclined with respect to the traveling direction of the charged particle beam on the surface on which the charged particle beam is irradiated, and has a cooling water flow path therein. .   The accelerator neutron source according to claim 7, wherein the metal target can be divided into a plurality of pieces. A charged particle source for generating charged particles;
An accelerator for accelerating the charged particles generated by the charged particle source;
A beam transport system for transporting a charged particle beam accelerated by the accelerator;
A boron neutron capture therapy system comprising the accelerator neutron source according to any one of claims 1 to 8, wherein the neutron is generated using the charged particle beam transported by the beam transport system. .

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