JP6632338B2 - Neutron chopper and neutron irradiation equipment - Google Patents

Description

  The present invention relates to a neutron chopper and a neutron irradiation device.

  The neutron beam irradiation device accelerates the charged particles and emits the charged particle beam, the target that generates the neutron beam by irradiating the charged particle beam emitted from the accelerator, and decelerates the neutron beam generated by the target And a speed reducer that performs the operation. The neutron beam irradiation device is used for a device that measures an internal state of an irradiation target. Specifically, a neutron beam is irradiated on the irradiated object by a neutron beam irradiation device, and a neutron beam transmitted through the irradiated object is detected using a neutron detector to obtain a transmission image of the irradiated object. There is a device.

  In the neutron beam irradiation device, as a device to select the timing or speed of the neutron beam irradiating the object to be irradiated or the neutron beam reaching the detector, the neutron beam is transmitted for a part of the time, the neutron beam for the remaining time Some use a chopper to shut off. In some neutron beam irradiation devices, a charged particle beam is irradiated in a pulse form from an accelerator.

  Patent Literature 1 discloses a device that controls the movement of a chopper by synchronizing the timing of a charged particle beam generated from an accelerator and the movement timing of a slit of a neutron chopper. Patent Literature 2 discloses a neutron disk chopper that rotates a disk having a passing portion that passes a neutron beam and a blocking portion that includes a neutron absorbing material that blocks the neutron beam. Further, it is described that the neutron disk chopper is formed such that the thickness of the disk is gradually reduced from the rotation center side toward the outer peripheral side.

U.S. Pat. No. 6,418,194 JP 2005-300487 A

  Here, the neutron chopper described in Patent Literature 2 has different thicknesses at the outer peripheral portion and the inner peripheral portion of the disk, so that the neutron shielding performance has a distribution. Further, the neutron chopper is required to pass more neutron rays of necessary components in order to operate the neutron beam irradiation device efficiently.

  Further, the device described in Patent Document 1 requires a mechanism for controlling the rotation of the neutron chopper. In addition, since the movement of the chopper, specifically the rotation, is adjusted by a mechanical mechanism, there is a gap between the input control command and the actual operation due to air resistance, frictional resistance of the bearing, bias of the chopper structure, etc. And rotation may become unstable, or there may be a limit in increasing control accuracy.

  An object of the present invention is to provide a neutron chopper and a neutron beam irradiation device capable of increasing energy efficiency by allowing more necessary neutron beams to pass therethrough.

  In a first aspect of the present invention, a plate-shaped disk in which a slit for passing a neutron beam is formed in a shielding portion for shielding a neutron beam, and a direction in which the disk intersects a surface having the largest area of the disk is defined as A neutron having a drive unit for rotating as a shaft, wherein the slit has a rotation axis of the disk and a wall surface in a cross section parallel to a radial direction of the rotation axis is inclined with respect to the rotation axis; Provide a chopper.

  In a second aspect of the present invention, a plate-shaped disk in which a slit for passing a neutron beam is formed in a shielding portion for shielding a neutron beam, and a direction in which the disk intersects a surface having the largest area of the disk is defined as There is provided a neutron chopper having a drive unit for rotating as a shaft, wherein the disk has a rotation axis inclined with respect to a traveling direction of the neutron beam.

  A third aspect of the present invention is directed to a plate-shaped disk in which a neutron beam shielding slit is formed in a shielding portion that shields a neutron beam, and the disk intersects a direction intersecting a surface having the largest area of the disk. A neutron chopper, characterized in that the neutron chopper includes a drive unit that rotates the disk, and the drive unit includes an angle varying device that changes an angle between a rotation axis of the disk and a traveling direction of the neutron beam.

  A fourth aspect of the present invention is directed to a neutron chopper according to any one of the above, wherein the charged particle beam converted to a neutron beam is irradiated in a pulsed manner, and the irradiation timing is adjustable. A position detection unit that detects the position of the slit of the chopper, and a detection result of the position detection unit, and an irradiation timing of the charged particle beam irradiated from the accelerator is determined based on the detection result of the position detection unit. And a radiation control device that generates a pulse for irradiating the charged particle beam to the accelerator based on the determined timing.

  ADVANTAGE OF THE INVENTION According to this invention, since a required neutron beam can be passed more, energy efficiency can be improved.

FIG. 1 is a schematic diagram illustrating an example of a neutron transmission imaging apparatus having a neutron beam irradiation apparatus. FIG. 2 is a front view showing a schematic configuration of the neutron chopper. FIG. 3 is a flowchart showing an example of the operation of the neutron irradiation device. FIG. 4 is an explanatory diagram for explaining an example of the operation of the neutron beam irradiation device. FIG. 5A is a sectional view taken along line AA of FIG. FIG. 5B is a cross-sectional view illustrating a schematic configuration of another example of the neutron chopper. FIG. 5C is a cross-sectional view illustrating a schematic configuration of another example of the neutron chopper. FIG. 6 is a side view showing a schematic configuration of another example of the neutron chopper. FIG. 7 is a top view showing a schematic configuration of another example of the neutron chopper. FIG. 8 is a front view showing a schematic configuration of another example of the neutron chopper.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings, but the present invention is not limited thereto. Components of each embodiment described below can be appropriately combined. In some cases, some components may not be used. The components in the following embodiments include those that can be easily replaced by those skilled in the art, or those that are substantially the same.

  In the following embodiments, the neutron beam irradiation device 1 is applied to an inspection device that irradiates a neutron beam N to an inspection target such as an apparatus or a structure and non-destructively inspects the inside of the inspection target. Will be described.

  FIG. 1 is a schematic diagram illustrating an example of a neutron transmission imaging apparatus having a neutron beam irradiation apparatus. As shown in FIG. 1, the neutron transmission imaging apparatus 100 includes a neutron beam irradiation device 1, a detector 12, a position detection device 13, and a control device 14.

  The neutron beam irradiation device 1 includes an acceleration device 2 that accelerates charged particles to emit a charged particle beam P, an adjustment device 3 that adjusts an irradiation state of the charged particle beam P emitted from the acceleration device 2, and a charged particle beam. A target 5 for generating a neutron beam N by irradiation of P, a speed reducer 6 for reducing the neutron beam N generated at the target 5, a collimator 7 for parallelizing the neutron beam N emitted from the speed reducer 6, and a chopper ( A neutron chopper) 10. The irradiation target S is irradiated with the neutron beam N emitted from the collimator 7. Further, the neutron beam irradiation device 1 switches between a state in which the irradiated neutron beam N is shielded by the chopper 10 and a state in which the irradiated neutron beam N is passed in a time-division manner.

  The accelerator 2 includes a circular accelerator or a linear accelerator. The accelerator 2 accelerates charged particles (protons, electrons, or heavy particles) to generate and emit a charged particle beam (proton beam, electron beam, or heavy particle beam) P. The accelerator 2 irradiates the charged particle beam P with a pulse, and can change the timing of the irradiating pulse. As the accelerator 2, for example, a linac accelerator can be used.

  The adjusting device 3 includes a plurality of electromagnets, and adjusts the irradiation state of the charged particle beam P emitted from the accelerator 2. The irradiation state of the charged particle beam P includes adjustment of the traveling direction of the charged particle beam P and shaping of the charged particle beam P. The adjusting device 3 suppresses the divergence of the charged particle beam P and focuses the charged particle beam P. The adjusting device 3 guides the charged particle beam P emitted from the acceleration device 2 to the scanning device 4.

  In the present embodiment, the neutron beam irradiation device 1 includes a scanning device 4 that scans the charged particle beam P. The scanning device 4 scans the charged particle beam P and adjusts the irradiation position of the charged particle beam P on the target 5. Further, the scanning device 4 shapes the charged particle beam P irradiated to the target 5. Note that the scanning device 4 may not be provided.

  The charged particle beam P emitted from the acceleration device 2 and having passed through the adjusting device 3 and the scanning device 4 is irradiated on the target 5. The target 5 generates a neutron beam N by irradiation of the charged particle beam P. The target 5 may be referred to as a neutron beam generating member 5. The target 5 includes a liquid or solid plate-shaped member formed of, for example, beryllium (Be), lithium (Li), or a compound containing them. The target 5 may be a circular or rectangular plate-like solid member, or may be heated liquid lithium. For example, liquid lithium continuously flowed so as to have a constant thickness may be used as the target 5.

  The speed reducer 6 reduces the speed of the neutron beam N generated at the target 5. The reduction gear 6 is disposed between the target 5 and the irradiation target S on the path of the neutron beam N. The target 5 generates high energy fast neutrons. The speed reducer 6 reduces the energy of fast neutrons and generates low-speed, low-energy neutrons (thermal neutrons, cold neutrons, or epithermal neutrons).

  The collimator 7 collimates the neutron beam N emitted from the reduction gear 6. The neutron beam N collimated by the collimator 7 and emitted from the collimator 7 is irradiated on the irradiation target S.

  The chopper 10 is disposed on a path to be irradiated with the neutron beam N, in this embodiment, between the collimator 7 and the irradiation target S. The chopper 10 includes a rotating unit (disk 20) having a shielding unit for shielding the neutron beam N and a passage unit (slit 26) for passing the neutron beam N, and a driving unit (driving unit 22) for rotating the rotating unit (disk 20). ), By switching the position of the passing portion, switching between a state in which the irradiated neutron beam N is shielded and a state in which the irradiated neutron beam N is allowed to pass. The state of reaching the body S is switched.

  FIG. 2 is a front view showing a schematic configuration of the neutron chopper. The chopper 10 has a disk 20 and a drive unit 22, as shown in FIGS. The disk 20 is a disk-shaped plate formed of a material or a mixture containing a neutron absorbing material such as lead or boron, which shields the neutron beam N. The drive unit 22 rotates the disk 20 about a rotation shaft 24. Here, the rotation shaft 24 is formed substantially at the center of the disk 20. The rotation axis 24 is in a direction parallel to the neutron beam irradiation direction.

  The disk 20 has a slit 26 extending in the radial direction of the disk, that is, in a direction away from the rotation shaft 24. The slit 26 has a shape in which a straight line passing through the rotation shaft 24 is the center line. In the slit 26 of the present embodiment, the width W on the surface of the disk 20, that is, the plane orthogonal to the rotation axis 24 is constant. In the disk 20, a portion where the slit 26 is formed corresponds to a passage portion that allows the neutron beam N to pass therethrough, and other portions correspond to a shielding portion that blocks the neutron beam N. The shape of the slit 26 of the disk 20 of the chopper 10 will be described later.

  The chopper 10 can rotate the position of the slit 26 by rotating the disk 20 by the drive unit 22. Accordingly, depending on the position of the slit 26 in the rotation direction, the position where the neutron beam N passes and the slit 26 overlaps and the state where the neutron beam N passes, and the position where the neutron beam N passes and the position where the slit 26 is not formed are as follows. The state in which the overlapping neutron beam N is shielded is switched.

  Here, the disk 20 has a diameter of 50 mm or more and 1000 mm or less. The thickness of the disk 20 varies depending on the material to be formed, but has a thickness necessary for shielding the neutron beam N, and is, for example, 10 mm or more and 500 mm or less. Further, the drive unit 22 exemplifies that the disk 20 is rotated at a frequency of 10 Hz or more and 1000 Hz or less (at least 10 rotations per second and at most 1000 rotations per second). The width W is preferably 0.5 mm or more and 100 mm or less. Further, it is preferable that the angle range of the slit 26 in the rotation direction be 0.05 degrees or more and 10 degrees or less. By setting the width W of the slit 26 to the above range or the angle range in the rotation direction to the above range, the chopper 10 can make the time required for the neutron beam N to pass through a predetermined range, thereby increasing the measurement accuracy. Can be.

  Next, the detector 12 is arranged in a direction in which the neutron beam N is irradiated from the neutron beam irradiation device 1. The detector 12 is arranged at a position facing the neutron irradiation device 1 with the irradiation target S interposed therebetween. In the detector 12, a detection element for detecting the neutron beam N is arranged on a surface facing the neutron beam irradiation device 1. The detector 12 detects a neutron beam N irradiated from the neutron beam irradiation device 1 and passed through a region where the irradiation target S is arranged, with a detection element. The detection elements are arranged in a matrix on the surface of the detector 12. The detector 12 sends the detection result to the control device 14.

  The position detection device 13 detects the position of the slit 26 of the disk 20 of the chopper 10, specifically, the position (phase) in the rotation direction. The position detecting device 13 may directly detect the position of the slit 26, or may detect the position of a marker provided on the disk 20, and may detect the position of the slit 26 from the relative position between the detected marker and the slit 26. Alternatively, the position of the slit 26 may be detected from the rotation operation of the drive unit 22. As the position detection device 13, an encoder using light transmission, a resolver using a rotary transformer, or an eddy current sensor capable of monitoring in a non-contact manner can be used. The position detecting device 13 sends the detected position information to the control device 14.

  The control device 14 controls the operation of each part of the neutron transmission imaging device 100. The control device 14 has an arithmetic processing function and a storage function. Further, the control device 14 has a function of an irradiation control device that controls the irradiation operation of the neutron beam irradiation device 1. The control device 14 includes a phase detection unit 14a that realizes the function of the irradiation control device, a comparison unit 14b, a trigger generation unit 14c, and a pulse generation unit 14d. Although the control device 14 of the present embodiment has shown the case where each unit is arranged in one block, each control function may be provided separately. For example, the control device 14 includes the phase detection unit 14a and the comparison unit 14b as one device inside the position detection device 13, and the trigger generation unit 14c and the pulse generation unit 14d as one device inside the acceleration device 2. May be provided.

  The phase detection unit 14a acquires the detection result of the position detection device 13 and detects the position of the slit 26 of the chopper 10. The phase detector 14a detects the timing at which the neutron beam N irradiated from the accelerator 2 and passed through the collimator 7 passes through the slit 26 based on the detected position of the slit 26 of the chopper 10. The comparison unit 14b compares the timing at which the neutron beam N detected from the position in the rotation direction of the slit 26 detected by the phase detection unit 14a passes through the slit 26 with the timing at which the accelerator 2 generates the charged particle beam P. Then, the difference between the two is detected. The trigger generation unit 14c generates a trigger signal serving as a trigger for generating a pulse for generating the charged particle beam P in the accelerator 2 based on the detected difference. The pulse generation unit 14d generates a pulse for generating the charged particle beam P based on the trigger signal. The control device 14 generates a pulse for generating the charged particle beam P and sends the generated pulse to the acceleration device 2 so that the pulsed charged particle beam P is emitted from the acceleration device 2.

  Next, the operation of the neutron irradiation apparatus 1 will be described with reference to FIGS. FIG. 3 is a flowchart showing an example of the operation of the neutron irradiation device. FIG. 4 is an explanatory diagram for explaining an example of the operation of the neutron beam irradiation device. The operations in FIGS. 3 and 4 can be realized by executing the operations in each unit of the control device 14.

  The control device 14 detects the current timing of the irradiation trigger of the charged particle beam (the timing of irradiating the charged particle beam) (step S12). The control device 14 may obtain the information from the information stored therein or the information from the accelerator 2. Next, the control device 14 detects the phase of the chopper (step S14). The detection result of the position detection device 13 is acquired, the position of the slit 26 of the chopper 10 is detected, and the neutron beam N irradiated from the accelerator 2 and passed through the collimator 7 based on the detected position of the slit 26 of the chopper 10. Is detected at the timing of passing through the slit 26.

  The controller 14 detects a difference between the phase of the chopper and the timing at which the beam passes through the slit (Step S16). That is, the timing at which the neutron beam N detected from the position in the rotation direction of the slit 26 detected by the phase detection unit 14a passes through the slit 26 and the timing at which the accelerator 2 generates the charged particle beam P are compared. The difference between the two.

  The control device 14 generates a trigger signal serving as a trigger for generating a pulse for generating a charged particle beam in the accelerator based on the detected difference (step S18). The control device 14 generates a pulse for generating the charged particle beam P based on the trigger signal (Step S20). The control device 14 generates a pulse for generating the charged particle beam P and sends the generated pulse to the acceleration device 2 so that the pulsed charged particle beam P is emitted from the acceleration device 2.

  As shown in FIG. 4, in the neutron beam irradiation device 1, a pulse 30 for generating an initial charged particle beam is shifted from a pulse 34 indicating a timing at which the slit 26 of the chopper is in a region where the neutron beam N passes. In this case, the timing for generating the charged particle beam is corrected to the pulse 32 for generating the charged particle beam. As described above, the neutron beam irradiation device 1 adjusts the generation timing of the charged particle pulse based on the phase of the slit of the chopper, so that the charged particle beam is emitted at the timing at which the desired neutron beam N passes through the slit 26. It can be generated by the acceleration device 2. In FIG. 4, the pulses 30 and 32 and the slit are used as the same timing with the pulse for generating the charged particle beam and the time when the neutron beam emitted and converted based on the charged particle pulse reaches the disk 20. Although the relation between the pulse 26 and the pulse 34 indicating the timing in the area where the neutron beam N passes is shown in an easy-to-understand manner, the relation is not limited to this. The pulses 30, 32 are the times at which the emitted and converted neutrons reach the disk 20 based on the charged particle pulse, and the actual charged particle pulse may be at another timing.

  The neutron beam irradiator 1 controls the timing of irradiating the charged particle beam from the accelerator 2 so that the neutron beam irradiator 1 can perform synchronous control without controlling hardware, specifically, a rotating device, and achieve high precision. Synchronization control becomes possible. Specifically, in order to adjust the movement of the chopper by a mechanical mechanism, specifically, the rotation, the input control command and the actual operation are controlled by air resistance, frictional resistance of the bearing, bias of the chopper structure, etc. It is possible to suppress the occurrence of a gap between them and the unstable rotation. In addition, since synchronization can be performed by electrical timing control, the control device can be simplified. In addition, the neutron beam irradiation device 1 can control the timing or speed of the neutron beam irradiating the irradiation target or the neutron beam arriving at the detector with high accuracy by enabling highly accurate synchronous control. . Thereby, the wavelength of the neutron beam reaching the detector 12 or the object S can be controlled with high accuracy, and the neutron beam whose energy is close to the peak can be applied to the detector 12 or the object S. Can be reached.

  In addition, the neutron beam irradiation device 1 uses a linac accelerator as the accelerator 2 and irradiates the charged particle beam with a pulse whose timing can be adjusted, so that the time for irradiating the charged particle beam can be shortened. Efficiency can be increased. Further, by shortening the irradiation time of the charged particle beam, the load on the member that shields the charged particle beam and the neutron beam can be reduced, and the energy of the charged particle beam at the time of irradiation can be increased.

  Here, it is preferable that the neutron beam irradiation device 1 irradiates the charged particles having a time t1 (pulse width) of 0.01 μsec or more and 1000 μsec or less from the accelerator 2, and the time t2 at which the chopper 10 passes the neutron beam is set. It is preferable that the period be 1 μsec to 100 μsec. As a result, the irradiated neutron beam can be converted into a shorter pulse neutron beam by the chopper 10. Thereby, the measurement accuracy can be further increased. Here, the neutron beam irradiation device 1 distributes the charged particle beam irradiated by the acceleration device 2 during the time t1 into a neutron beam at the target 5 and then passes through the speed reduction device 6 to distribute the neutron beam speed. Occurs. For this reason, the time during which the neutron beam passes through the area where the chopper 10 is disposed is longer than the time t1 during which the accelerator 2 irradiates the charged particle beam, and is, for example, 10 μsec or more and 100 μsec or less. As described above, even when the time t1 during which the charged particle beam is irradiated from the accelerator 2 is shorter than the time t2 during which the chopper 10 passes the neutron beam, the irradiated neutron beam is used as a neutron beam with a shorter pulse by the chopper 10. be able to. When the accelerator 2 is a proton accelerator, it is preferable that the accelerator 2 emits a charged particle beam having a time t1 of 10 μsec or more and 1000 μsec or less.

  Further, in the neutron beam irradiation device 1 of the present embodiment, the chopper 10 is disposed between the collimator 7 and the irradiation target S in the neutron beam N passage path, but the present invention is not limited to this. In the neutron beam irradiation device 1, the chopper 10 may be arranged between the speed reducer 6 and the collimator 7.

  Next, the shape of the slit 26 of the disk 20 of the neutron chopper 10 will be described. FIG. 5A is a sectional view taken along line AA of FIG. 5B and 5C are cross-sectional views each showing a schematic configuration of another example of the neutron chopper. The disk 20 of the neutron chopper (chopper) 10 shown in FIG. 5A has a slit 26 having a width w. The slit 26 has a rotating shaft 24 of the disk 20 and a wall surface 27 in a cross section parallel to the radial direction of the rotating shaft 24 is inclined with respect to the rotating shaft 24. The angle between the wall surface 27 and a line parallel to the rotation axis 24 is θ. Here, with respect to the rotation direction 29 of the disk 20 at the cross section at the position where the neutron beam N passes, the disk 20 moves in a direction in which the wall surface 27 on the front side (upstream side) in the rotation direction advances in the traveling direction of the neutron beam N. It is inclined in the direction toward the rear. With respect to the rotation direction 29 of the disk 20 at the cross section at the position where the neutron beam N passes, the disk 20 moves rearward as the wall surface 27 on the rear side (downstream side) in the rotation direction advances in the traveling direction of the neutron beam N. It is inclined in the direction toward.

  The neutron chopper (chopper) disk 20a shown in FIG. 5B has a slit 26a having a width w. In the slit 26a, the rotation axis 24 of the disk 20a and a wall surface 27a in a cross section parallel to the radial direction of the rotation axis 24 are inclined with respect to the rotation axis 24. The angle between the wall surface 27 and a line parallel to the rotation axis 24 is θa. The disk 20a has the same structure except that the angle θa is different from the angle θ of the disk 20.

  In contrast, a neutron chopper (chopper) disk 20b shown in FIG. 5C has a slit 26b having a width w. The wall surface of the slit 26 b in a section parallel to the rotation axis 24 of the disk 20 b and the radial direction of the rotation axis 24 is parallel to the rotation axis 24.

  The disks 20, 20a have a shape in which the slits 26, 26a are inclined with respect to the rotation axis 24, so that the neutron beam (more specifically, the neutron beam that has entered the slits 26, 26a on the entrance side of the slits 26, 26a). Among the neutron beams at the velocity to be passed), the neutron beams that collide with the wall surfaces 27 and 27a of the slit on the way can be reduced. In addition, the neutron beam to be shielded can be shielded by portions other than the slits 26 and 26a. As a result, the disks 20, 20a collide with the wall surfaces 27, 27a of the slits 26, 26a of the neutron beam of energy (velocity) used for measurement, as compared with the case where the neutron beam passes through the slit 26b of the disk 20b. The amount of the neutron beam can be reduced, and the neutron beam energy (velocity) used for measurement after passing through the chopper can be increased. Further, the disks 20, 20a are formed such that the slits 26, 26a are inclined with respect to the rotation shaft 24, so that even if the rotation speed of the disks 20, 20a is increased, the thickness is increased, Even when the depth of 26a (the length in the direction in which the neutron beam travels) is long, the amount of neutron beam that collides with the wall surfaces 27 and 27a of the slits 26 and 26a can be reduced, and the number of neutrons passing through the chopper 10 can be reduced. You can do more. Further, the disks 20, 20a have a shape in which the slits 26, 26a are inclined with respect to the rotation axis 24, so that the neutron beam entering the slits 26, 26a at a predetermined speed and the wall surfaces 27, Since it is possible to make the shape hard to collide with 27a, the range of the neutron energy passing through the slits 26, 26a can be widened. In addition, the disks 20, 20a do not need to be changed in the arrangement of the entire disks, so that they do not affect the installation space. Thereby, it is possible to efficiently pass the neutron beam while increasing the degree of freedom in designing the entire apparatus.

  In the disk 20, the angle (inclination angle) θ between the wall surface 27 of the slit 26 and a line parallel to the rotation axis 24 is preferably 3 degrees or more and 45 degrees or less. By setting the angle to 3 degrees or more, it is possible to suppress absorption of neutron beams having a low speed, and to set the angle to 45 degrees or less, it is possible to suppress absorption of neutrons having a high speed. Thereby, a neutron beam to be passed at a speed in the range of about 300 m / s or more and about 1000 m / s or less, specifically, a cold neutron beam (energy range of about 0.5 meV or more and about 5 meV or less) or about 1000 m / s or more Specifically, a thermal neutron beam (energy range of about 5 meV or more and about 100 meV or less) at a speed of about 5000 m / s or less can easily pass through the slit 26. The moving speed of the disk 20 at a radial position where the neutron beam passes through the slit 26 is, for example, 300 m / s, but the disk 20 is rotated within a range of the moving speed of the disk 20 at a radial position at which a general neutron passes through the slit 26. In this case, by adjusting the angle θ in the range of 3 degrees or more and 45 degrees or less, it is possible to allow more neutron rays to pass through in a desired range of speed and energy.

  Further, in the present embodiment, in a cross section orthogonal to the radial direction of the rotating shaft 24 of the disk 20, the width of the slit 26 is formed to be constant in the traveling direction of the neutron beam N, but is not limited thereto. The disk 20 may have a shape in which the width w decreases or increases as the neutron beam N advances in the traveling direction.

  With respect to the rotation direction 29 of the disk 20 at the cross section at the position where the neutron beam N passes, the disk 20 moves rearward as the wall surface 27 on the rear side (downstream side) in the rotation direction advances in the traveling direction of the neutron beam N. Of the neutron beam N that has entered the slit 26, it is possible to suppress the neutron beam N of the speed to be passed from colliding with the wall surface 27 on the rear side in the rotation direction. Therefore, as the disk 20 moves in the direction in which the neutron beam N travels, the wall surface 27 on the rear side (downstream side) in the rotation direction with respect to the rotation direction 29 of the disk 20 at the cross section at the position where the neutron beam N passes. Preferably, it is inclined in the direction toward the rear side.

  In the above embodiment, the direction of the wall surface 27 of the slit 26 of the disk 20 is inclined with respect to the traveling direction of the neutron beam N, but is not limited to this. FIG. 6 is a side view showing a schematic configuration of another example of the neutron chopper. FIG. 7 is a top view showing a schematic configuration of another example of the neutron chopper. The neutron chopper 10a shown in FIGS. 6 and 7 includes a disk 20, a drive unit 22, and an angle varying device 80. The disk 20 and the drive unit 22 are the same as in the above embodiment. The disk 20 has a slit 26 formed in parallel with the rotating shaft 24.

  The angle varying device 80 rotates the drive unit 22 about the rotation axis 90. The rotation axis 90 passes through the rotation axis 24 of the disk 20, passes through a center line CL parallel to the traveling direction of the neutron beam N, and passes through the center of the disk 20 in a cross section orthogonal to the radial direction of the disk 20. The angle varying device 80 includes a rotating plate 81 that rotates around a rotating shaft 90, a connecting portion 82 that connects the rotating plate 81 and the driving unit 22, and a driving unit 84 that rotates the rotating plate 81. The angle varying device 80 rotates the rotating unit 22 a around the rotation axis 90 by rotating the rotation plate 81 around the rotation axis 90 by the driving unit 84. Thereby, the disk 20 rotates around the rotation axis 90 (direction R). As the disk 20 rotates around the rotation axis 90, the wall surface of the slit 26 is inclined with respect to the traveling direction of the center line CL and the neutron beam N.

  As described above, the disk 20 is inclined with respect to the traveling direction of the neutron beam N, the rotation axis 24 of the disk 20 is inclined with respect to the traveling direction of the neutron beam N, and the slit 26 of the disk 20 is oriented in the traveling direction of the neutron beam N. The amount of the neutron beam N that collides with the wall surface 27 of the slit 26 can be reduced by inclining the neutron beam N, and the yield of the energy (speed) neutron beam N used for measurement after passing through the chopper can be increased. .

  In FIG. 7, assuming that the angle (inclination angle) between the traveling direction of the neutron beam N and the center of the slit 26 is ρ, it is preferable that the angle ρ is not less than 3 degrees and not more than 45 degrees like the angle θ. By setting the angle to 3 degrees or more, it is possible to suppress absorption of neutron beams having a low speed, and to set the angle to 45 degrees or less, it is possible to suppress absorption of neutrons having a high speed. The angle ρ is also an angle at which the disk 20 rotates with respect to a direction orthogonal to the center line CL.

  Further, in the present embodiment, the angle ρ formed by the angle varying device 80 can be adjusted, so that the angle ρ formed can be adjusted according to the conditions of the neutron beam that has passed through the slit. Thereby, the amount of the neutron beam to be passed can be controlled as needed. For this reason, it is preferable that the disk 20 be capable of adjusting the angle ρ formed by the angle varying device 80. However, the disk 20 has a structure in which the disk 20 is fixed at a fixed angle while being inclined with respect to the traveling direction of the neutron beam N. Is also good.

  FIG. 8 is a front view showing a schematic configuration of the neutron chopper. The disc 20c of the neutron chopper 10b shown in FIG. 8 includes a first portion 40 including a portion in which the slit 26 is formed, a second portion 41 provided with a rotation shaft rotated by the driving unit, A fixing portion for fixing the portion to the second portion in a detachable manner. The first portion 40 is preferably an area smaller than the second portion 41. Specifically, the first portion 40 is preferably 10% or less of the second portion 41. The fixing portion 42 is a mechanism that can fix the first portion 40 to the second portion 41 and supports the first portion 40 so as not to come off from the second portion 41 even when the disk 20c is rotated. For the fixing portion 42, for example, a fastening member such as a bolt or a nut for fastening the first portion 40 to the second portion 41 or a bolt fastened to at least one of the first portion 40 and the second portion 41 is used. Can be.

  The neutron chopper 10b is provided with a plurality of types of first portions 40 having slits formed at different angles θ between the rotation axis and the wall surfaces of the slits. Different choppers can be installed. As a result, it is possible to reduce the material cost for manufacturing the disc and the time required for replacement.

DESCRIPTION OF SYMBOLS 1 Neutron irradiation apparatus 2 Accelerator 3 Adjuster 4 Scanner 5 Target 6 Reduction gear 7 Collimator 10 Chopper (neutron chopper)
12 Detector 13 Position detection device 14 Control device (irradiation control device)
14a Phase detection unit 14b Comparison unit 14c Trigger generation unit 14d Pulse generation unit 20 Disk 22 Drive unit 24 Rotation axis 26 Slit 28 Outer shielding unit N Neutron beam P Charged particle beam S Irradiated object

Claims (7)

A plate-shaped disk in which a slit for passing a neutron beam is formed in a shielding portion for shielding a neutron beam,
A drive unit that rotates the disk around an axis that intersects a plane having the largest area of the disk,
A neutron chopper, wherein the slit has a rotation axis of the disk and a wall surface in a cross section parallel to a radial direction of the rotation axis inclined with respect to the rotation axis.   2. The neutron chopper according to claim 1, wherein an inclination angle of the wall of the slit with respect to a rotation axis of the disk is 3 degrees or more and 45 degrees or less. 3. A first portion including a portion in which the slit is formed;
A second portion provided with a rotation shaft that is rotated by the driving portion;
Neutron chopper according to claim 1 or 2, characterized in that it has a, a fixing portion for fixing in a state capable of detachably said first portion to said second portion. An accelerator that irradiates a charged particle beam converted to a neutron beam in a pulse shape, and that can adjust the irradiation timing;
A neutron chopper according to any one of claims 1 to 3 ,
A position detection unit that detects the position of the slit of the neutron chopper,
Detecting the detection result of the position detection unit, based on the detection result of the position detection unit, determines the irradiation timing of the charged particle beam irradiated from the acceleration device, based on the determined timing, the acceleration device A radiation control device that generates a pulse for irradiating the charged particle beam. The irradiation control device detects a passage timing at which the neutron beam passes through the slit of the neutron chopper based on a detection result of the position detection unit, and detects the detected passage timing and the current irradiation timing of the charged particle beam. 5. The neutron beam irradiation apparatus according to claim 4 , wherein the irradiation timing of the charged particle beam is determined based on the comparison result. The accelerator, the pulse width is irradiated with charged particles of 0.01 μsec or more and 1000 μsec or less,
The neutron chopper, neutron beam irradiation apparatus according to claim 4 or 5, characterized in that between the inclusive 1μ seconds 100μ seconds, passing said neutron beam. The accelerator is a neutron beam irradiation apparatus according to any one of claims 4 6, characterized in that it comprises a linac accelerator.

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