JP2014115123A - Neutron generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the generation amount of secondary γ-rays is large due to the irradiation curing and irradiation by neutrons.SOLUTION: A flow path 2 provided inside a chamber 3 is formed of a carbon material or its compound, preferably a CIP material of graphite particles. A rectification part 1 is connected to this flow path 2. An end part of the rectification part 1 is formed with a nozzle 11, and a discharge port is positioned upper side by a prescribed distance from the same face or the bottom face as the flow path 2. The bottom face of the rectification part is arranged with a thin-plate like liner made of a low activation ferrite steel or a general metal material. Liquid lithium is changed into a film flow and discharged from the discharge port. Proton beams are irradiated from a proton beam incident pipe 4. When the proton beams are irradiated, neutrons are generated at a target region and pass through the flow path 2 and a chamber 3 though being irradiated in all directions, and are sufficiently irradiated downward with some directivity. Consequently, the generation amount of the secondary γ rays can be suppressed by forming the flow path 2 using a carbon material or a compound thereof.

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 the liquid lithium circulation device, a technique described in Patent Document 1 is known.

  The liquid lithium circulation device described in Patent Document 1 has a structure in which a jet of liquid lithium is flowed from a two-stage contraction nozzle onto a substantially horizontal flow path. And is housed in an airtight chamber. These chambers and flow paths are made of SUS304, but when they are actually used in BNCT, it is planned to use a metal material that is co-supporting with lithium, such as low activation ferritic steel. Since the liquid lithium circulation device described in Patent Document 1 is an experimental device, no neutron irradiation device is provided.

Experimental study on IFMIF liquid metal lithium target flow Horiike, Kondo, Kanamura et al. J. Plasma Fusion Res. Vol.84, No.9 (2008) 600-605

  However, when neutrons are irradiated to liquid lithium flowing through the flow path in a conventional liquid lithium circulation system, metallic materials such as ferritic steel and stainless steel generate many secondary gamma rays due to the neutron irradiation stopping power due to the neutron irradiation stopping power. There was a problem of doing. The present invention has been made to solve such problems.

  In the neutron generator according to the present invention, a proton beam irradiation position is set at a predetermined position, and at least a certain region including the irradiation position is a carbon material, a carbon fiber composite material, SiC, a SiC fiber composite material or a mixture thereof, or aluminum It is made of a light element material such as an aluminum alloy, titanium, or titanium alloy (hereinafter referred to as “carbon-based material”) and has a bowl-shaped flow path through which a liquid metal flows.

  According to the present invention, since the portion including the irradiation position of the proton beam is composed of at least a carbon material or a compound thereof, the generation amount of secondary γ rays accompanying neutron irradiation is suppressed. It is also included that the entire channel is made of a carbon-based material or the like. The irradiation position includes, for example, a region having a radius of about 0.2 m through which neutron rays are transmitted and scattered. The discharge port of the nozzle may be disposed on the same plane as the bottom surface of the flow path, or the discharge port may be disposed slightly above the bottom surface. Further, it is assumed that the neutron generator can be installed from a substantially horizontal direction to a substantially vertical direction.

  Further, in the neutron generator, when the liquid metal is discharged from the bottom surface of the flow path at a predetermined speed, the liquid metal discharge port extends from the proton beam irradiation position to a downstream region. It is preferable to provide it at a position where the jet can be blown off.

  In this way, since the liquid metal jet is in the air at the proton beam irradiation position, even if the irradiation position of the flow path is made of a carbon-based material or the like, the flow state of the liquid metal target is It does not depend on the surface condition.

  In the neutron generator, the flow path and the nozzle are housed in an airtight chamber, and the chamber is a carbon material, a carbon fiber composite material, SiC, a SiC fiber composite material or a mixture thereof, aluminum, aluminum alloy, titanium. It is preferable to use a light element material such as a titanium alloy.

  Furthermore, in the neutron generator, it is preferable that the flow path is provided with a thin plate liner made of a metal material compatible with lithium, such as a low activation metal. The liner is preferably installed to be slidable with respect to the flow path.

  Furthermore, in the neutron generator, the carbon material or the compound constituting the flow path is preferably formed by sintering graphite particles.

It is a block diagram which shows the neutron generator concerning embodiment of this invention. It is AA sectional drawing of FIG. It is an enlarged view of the discharge outlet of the neutron generator shown in FIG. FIG. 4 is a partially enlarged view of FIG. 3. It is BB sectional drawing of FIG.

  FIG. 1 is a block diagram showing a neutron generator according to an embodiment of the present invention. 2A is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 2B is a partial cross-sectional view thereof. FIG. 3 is an enlarged view of the discharge port, and FIG. 4 is an enlarged view of FIG. 5 is a cross-sectional view taken along the line BB in FIG. The neutron generator 100 includes a rectifying unit 1 having a honeycomb plate or a plurality of porous plates, a flow channel 2 connected to the rectifying unit 1 and through which a discharged liquid lithium jet flows, and a chamber 3 that houses the flow channel 2. With.

  The downstream end 31 of the chamber 3 is squeezed in a funnel shape, and its tip is connected to a tank (not shown) through a pipe. A proton beam incident tube 4 that receives a proton beam is provided at a substantially upper center portion of the chamber 3. Further, the chamber 3 is provided with a vacuum exhaust port 5 for sucking internal air and gas. The vicinity of the downstream end 31 of the chamber 3 has a stretchable structure with a bellows 7 attached to absorb expansion and contraction caused by heat. Further, since the inside of the chamber 3 is evacuated from the evacuation port 5, a portion where the rectifying unit 1 is engaged is processed with high airtightness. Further, as shown in FIGS. 2 and 5, the chamber 3 has a semicircular cross section or a rectangular cross section with rib reinforcement.

  The chamber 3 is formed from a light element material such as C / C composite, graphite sheet, SiC, SiC fiber composite material, carbon fiber reinforced plastic, aluminum, aluminum alloy, titanium, titanium alloy, or the like. By configuring the chamber 3 with a carbon-based material or the like, it is possible to suppress the generation amount of secondary γ rays and achieve low radiation. In particular, since the chamber 3 is close to the patient to be treated, it is preferable to use a structural material that suppresses the generation amount of secondary gamma rays. In addition, it is composed of a double structure material in which corrugated sheets or honeycomb structures made of similar materials are disposed between two steel sheets, a corrugated cardboard structure material in which a corrugated core is sandwiched between two steel sheets, or a combination thereof. It may be done (not shown).

  The channel 2 has a bowl shape with a rectangular channel cross section, one end 21 connected to the rectifying unit 1 on the one end 32 side of the chamber 3, and the other end 22 positioned near the downstream end 31 of the chamber 3. To do. The flow path 2 is supported by the bottom 33 in the chamber 3 by a support member (not shown). The flow path 2 is slightly inclined with respect to the horizontal direction as shown in FIGS. 2 to 4 so that liquid lithium finally flows down from the flow path 2 when the circulation is stopped. In the flow path 2, the position immediately below the proton beam incident tube 4 is the proton beam irradiation position.

  The flow path 2 is composed of a carbon material, a carbon fiber composite material, SiC, a SiC fiber composite material, or a mixture thereof, or a light element material such as aluminum, aluminum alloy, titanium, or titanium alloy. In particular, it is preferable to use a material having a small neutron stopping ability and a small absorption cross section. Specifically, the flow path 2 is preliminarily molded into a bowl shape by a cold isostatic press (CIP: Cold Isostatic Press) and heated for a predetermined time at 1400 ° C. in a furnace. It is manufactured by sintering. Alternatively, a SiC fiber composite material is used, and the bottom surface 23 of the flow path 2 is smoothed to a predetermined surface roughness by machining. The side wall 24 is also preferably smoothed to a predetermined surface roughness by machining. By comprising these carbon-based materials, the effect of suppressing the generation of secondary gamma rays by neutrons can be obtained. By configuring the flow path 2 with a carbon-based material, irradiation hardening and irradiation embrittlement, which are problems with the low activation ferritic steel, do not occur, and maintenance load such as replacement of the flow path 2 is reduced.

  A liner 8 may be provided on the surface of the flow path 2. The liner 8 is made of a thin metal plate that has high coexistence with lithium, such as low activation ferritic steel, and is difficult to be activated, and is covered on the bottom surface 23, the side wall portion 24, and the upper end surface 25 of the flow path 2. It is preferable to use a thin liner 8 in order to suppress the generation of secondary gamma rays. Specifically, it is good to set it as 0.2 mm-1.0 mm. Since the liner 8 prevents the lithium particles from entering the carbon structure, the flow path 2 can be prevented from cracking. Further, the surface roughness of the liner 8 is set to about Ra0.4 to Ra1.6 so that liquid lithium flows smoothly. In addition, the liner 8 is not fixed to the flow path 2 but is configured to slide relative to the flow path 2 in the longitudinal direction of the flow path 2.

  The tip of the rectifying unit 1 is a two-stage contraction nozzle 11. The nozzle 11 is made of low activation ferritic steel. The nozzle 11 rides on the end of the flow path 2 and absorbs a difference in thermal expansion such as a slight gap between the nozzle 11 and the bottom surface 23 of the flow path 2 due to a difference in linear expansion coefficient with the flow path 2. Provide structure. The gap S is about 0.5 mm in the vertical direction and about 1 mm to 3 mm in the horizontal direction depending on the length of the rectifying unit 1. Further, the discharge port 12 of the nozzle 11 has a band shape, and a mountain-shaped groove 13 is formed in the lower portion thereof. The groove 13 makes the lower edge portion 12a of the discharge port 12 have an acute angle, thereby suppressing the disturbance of the free surface after the discharge of liquid lithium. Further, the end edge portion 12 b of the nozzle 11 also protrudes at an acute angle with respect to the bottom surface 23 of the flow path 2. For example, the slope angle α of the mountain-shaped groove 13 is 45 ° with respect to the bottom surface 23.

  The end portion 81 of the liner 8 is bent from the bottom surface 23 of the flow path 2 and is inclined upward to reach the top portion 13 b of the mountain-shaped groove 13. Since the end portion 81 of the liner 8 covers the gap S between the nozzle 11 and the bottom surface 23, the discharged liquid lithium is prevented from entering the gap S. Further, by fixing the end portion of the liner 8 only to the groove 13, the end portion of the liner 8 is not separated from the discharge port 12, and the liner 8 is thermally expanded on the channel 2 with the end portion as a base point. Will slide.

  The height h of the lower edge portion 12a of the discharge port 12 is such that when liquid lithium is discharged from the nozzle 11 at a predetermined flow rate (high flow rate of 10 m / s or more), the jet of liquid lithium is in the air at the proton beam irradiation position. The height that can be achieved. For example, the height h is 3 mm for a flow rate of 20 m / s. The position of the proton beam injection tube 4 is 50 mm to 350 mm from the discharge port 12 of the nozzle 11. In this positional relationship, when liquid lithium is ejected from the nozzle 11 at a flow velocity of 20 m / s, the main stream portion of the liquid lithium is ejected as a film flow in a state where it floats from the bottom surface 23, and the liquid lithium film is ejected at the proton beam irradiation position. A target consisting of a stream is formed.

  Further, even if a minute deformation occurs in the metal liner 8 due to the thermal cycle, the liquid lithium is flying in the air, and since it has already been irradiated with the proton beam at the landing point, it is not affected by the minute deformation.

  Next, operation | movement of this neutron generator 100 is demonstrated. When liquid lithium is introduced into the rectifying unit 1 by a pump (not shown), the flow of liquid lithium is adjusted by the honeycomb and the porous plate, and is discharged from the discharge port 12 of the nozzle 11. The speed of the liquid lithium jet when discharging from the nozzle 11 is increased to a predetermined value. Further, since the lower end portion 12a of the discharge port 12 of the nozzle 11 is located, for example, 3 mm above the bottom surface 23 of the flow path 2, the jet of liquid lithium becomes a film and floats from the bottom surface 23 of the flow path 2 Fly through the air in a state. The jet of liquid lithium ejected at this speed flies further downstream than the position of the proton beam incident tube 4 while freely falling by gravity, and approaches the bottom surface 23 of the flow path 2 at the end, and finally reaches the bottom surface 23. It reaches and flows on the flow path.

  At this time, a liner 8 is disposed on the bottom surface 23, and a jet of liquid lithium hits the surface of the liner 8 and does not hit the surface made of the carbon-based material below the liner 8. It is possible to prevent liquid lithium from being impregnated and causing the flow path 2 to crack due to expansion and contraction. Moreover, the liner 8 is a metal, the flow path 2 is a carbonaceous material, and these have different linear expansion coefficients. The liner 8 and the bottom surface 23 are not in a structure that restrains each other, but are in a slide structure in which no stress is generated even by a thermal cycle due to temperature rise / fall of the device, so that the liner 8 is not deformed, There is no crack in the path 2. Further, since the liner 8 prevents the jet of liquid lithium from being directly sprayed onto the bottom surface 23, the effect of preventing the carbon-based material portion from being cracked by the liner 8 is ensured even if the liner 8 is peeled off. Furthermore, since the liner 8 is not a structure fixed to the flow path 2, it can be easily replaced.

  Further, when the liquid lithium jet is ejected to the flow path 2, the jet is hollow and does not directly contact the bottom surface 23, but the liquid lithium jet is always sprayed on the side wall 24. . However, since the side wall 24 is also covered with the liner 8, liquid lithium is prevented from entering between the carbon-based particles, and the side wall 24 is prevented from cracking. In particular, by preventing the side wall 24 from cracking, it is possible to prevent liquid lithium from leaking from the flow path 2 and spilling to the outside.

  Furthermore, since the liner 8 is also disposed on the upper end surface 25, the crack of the flow path 2 and spilling to the outside are also prevented on the upper end surface 25. In addition, when the flow velocity at the time of discharge is low, such as at the start of operation, the liquid lithium jet gradually flies into the air gradually from the discharge port 12 while hitting the liner 8 on the bottom surface 23. As described above, even if liquid lithium spills out before discharge port 12 due to liquid lithium spillage and ejection in the initial stage, liquid lithium can be prevented from impregnating into the carbon particles.

  In addition, a liquid lithium jet is formed in a state of floating from the bottom surface 23 of the flow path 2 and becomes a target for proton beam irradiation. When this target is irradiated with a proton beam, neutrons are generated, and the neutrons are emitted from the target. The liner 8 located below is irradiated. Here, secondary gamma rays are generated slightly, but since the liner 8 itself is formed of a thin plate, the amount of secondary gamma rays generated is extremely low compared to the case where the entire flow path is made of a structural metal. . This is preferable for patients receiving neutron irradiation.

  Moreover, since carbon materials are difficult to be activated, there is an effect of reducing the amount of waste. And since the irradiation hardening and the irradiation embrittlement which were the subject with low activation ferritic steel are hard to occur, the flow path 2 is easy to maintain an initial mechanical characteristic, and maintenance frequency, such as replacement | exchange, also decreases. Further, although a metal material is used for the liner 8, the liner 8 is not a member having mechanical strength. Therefore, there is no need for replacement unless a crack occurs even if irradiation hardening or irradiation embrittlement occurs. Moreover, if it is only the liner 8, since the volume as a radioactive waste after replacement | exchange is small, it is easy to dispose.

  Neutrons generated at the target pass through the flow path 2 and the chamber 3 and travel downward.

  As described above, according to the neutron generator 100 of the present invention, the amount of secondary γ rays generated due to generation and irradiation of neutrons can be minimized. Also, safety risks associated with irradiation hardening and irradiation embrittlement can be minimized. For this reason, the frequency of maintenance such as replacement is reduced, and the running cost is reduced.

  In addition, you may comprise only a part including the irradiation position of a proton beam among the flow paths 2 with a carbon material (illustration omitted). For example, a CIP material of graphite particles may be provided in a flow path made of low activation ferritic steel. The position where the CIP material is fitted may be in a range of 350 mm from the end of the flow path 2 on the discharge port 12 side. Further, the liner 8 may be omitted. In this case, even if liquid lithium is impregnated between the graphite particles and micro unevenness or the like is generated on the surface, if the liquid lithium film flow is flying at the proton beam irradiation position, the state of the target surface is It will not be affected.

  It is also possible to eliminate the height h of the lower edge portion 12a of the discharge port 12 and make it the same height as the bottom surface 23 (the surface of the liner 8) (not shown). In this case, the liquid lithium flows using the bottom surface 23 of the flow path 2 as a back wall.

  In the above embodiment, the configuration example in which the entire neutron generator 100 is installed in the horizontal direction is shown, but the entire apparatus may be installed in a substantially vertical direction. Specifically, when the flow path 2 is an upright vertical flow path, the function of maintaining the flatness of the lithium jet and the function as a proton beam penetration prevention wall are the main functions of the flow path 2. .

  Then, neutrons are generated by irradiating the target with a proton beam. This neutron is irradiated to the affected part of the patient standing near the target. Thus, when the neutron generator 100 is installed in a substantially vertical direction, the patient can receive treatment in a standing posture or a sitting posture.

DESCRIPTION OF SYMBOLS 100 Neutron generator 1 Rectification part 2 Flow path 23 Bottom face 24 Side wall part 3 Chamber 4 Proton beam injection tube 5 Vacuum exhaust port 8 Liner

Claims (6)

A discharge port of a nozzle that discharges liquid metal is disposed at the end, and an irradiation position of the proton beam is set at a predetermined position, and at least a certain region including the irradiation position is a carbon material, a carbon fiber composite material, SiC, A neutron generator characterized by comprising an eaves-like channel made of a SiC fiber composite material or a mixture thereof, or a light element material such as aluminum, aluminum alloy, titanium, or titanium alloy, and through which a liquid metal flows. Further, the discharge port is provided at a position above the bottom surface of the flow path so that the liquid metal jet can be blown from the proton beam irradiation position to the downstream area when the liquid metal is discharged at a predetermined speed. The neutron generator according to claim 1. The flow path and the nozzle are housed in an airtight chamber, and the chamber is a carbon element, a carbon fiber composite material, SiC, a SiC fiber composite material or a mixture thereof, or a light element material such as aluminum, aluminum alloy, titanium, or titanium alloy. The neutron generator according to claim 1 or 2, characterized by comprising: The neutron generator according to any one of claims 1 to 3, wherein a thin plate liner made of a metal material excellent in coexistence with lithium is provided in the flow path.   The neutron generator according to claim 1, wherein the liner is slidably installed with respect to the flow path. The neutron generator according to any one of claims 1 to 5, wherein the carbon material constituting the flow path is formed by sintering graphite particles.

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