Neutron detector for performance testing of boron neutron capture therapy

Abstract

The present invention relates to a neutron detector, and the neutron detector of the present invention is configured so that the relative position of the moderator to the sensor is variable, allowing measurements to be made while the position of the moderator or the sensor is moved.The neutron detector of the present invention is configured so that a number of cylindrical structures are concentrically stacked in the axial direction, and the diameter of each cylindrical structure becomes smaller from the rear to the front along the axial direction, making it possible to detect neutrons having high energy to neutrons having low energy.

Description

[Technical Field]

[0001] The present invention relates to a neutron detector, and more particularly to a neutron detector that measures the neutron energy spectrum over a wide energy range from thermal neutrons to fast neutrons generated in boron neutron capture therapy. [Background technology]

[0002] Boron Neutron Capture Therapy (BNCT) is a new radiation therapy method that involves injecting drug-treated boron into the patient, then selectively killing only cancer cells with epithermal neutrons, and a single treatment can achieve the same effect as 20 to 30 conventional radiation treatments. BNCT requirements are stated in the IAEAL23-01601 technical document (Advances in Boron Neutron Capture Therapy), and require that the epithermal neutron (0.5 eV to 10 keV) flux of a BNCT treatment facility must be 5 x 10 8 cm -2 s -1 The BNCT neutron flux measurement method uses a fission chamber or gold foil. The former method is incapable of measuring high flux, and the latter method is passive and therefore incapable of real-time monitoring. Neutron spectrum measurement methods include the multi-foil activation method and the Bonner sphere measurement method using a proportional counter. These two methods have the disadvantages of being passive and incapable of measuring high flux, respectively.

[0003] Figure 1 shows photographs of conventional Bonner sphere spectrometers of various sizes and a diagram illustrating the response function for neutron energy. Referring to Figure 1(a), a Bonner sphere spectrometer consists of moderators of various sizes (usually spherical or cylindrical) and a thermal neutron detector (usually a 3He proportional counter or BF3 proportional counter). The thermal neutron detector, called a Bonner sphere, is inserted inside each moderator. Hereinafter, each Bonner sphere is placed in the neutron field whose energy spectrum is to be measured, and the count rate of the thermal neutron detector is measured. The response of each Bonner sphere to neutron energy is calculated using Monte Carlo computer simulation, and the response function is obtained, as shown in Figure 1(b). The neutron energy spectrum can be calculated using the measured neutron count rate and response function, which is called unfolding.

[0004] Previously, Japanese Patent No. 5798724 (issued August 28, 2015) disclosed a neutron spectrum measurement device using Bonner spheres. However, as shown in Figure 1(a), a Bonner sphere spectrometer typically consists of polyethylene moderators ranging from 2 to 12 inches. When approximately ten polyethylene moderators are used, the device weighs more than 50 kg. Furthermore, because the same thermal neutron detector is used, the thermal neutron detector must be replaced when measuring Bonner spheres of different sizes. Therefore, the measurement time is extended by the time required to replace the Bonner sphere. Furthermore, when using a Bonner sphere spectrometer, it is impossible to perform measurements in a space smaller than the radius of the Bonner sphere when the largest Bonner sphere is installed. The epithermal neutron flux required for BNCT is usually measured at the beam output port surface of the BNCT treatment room (usually a circle with a diameter of approximately 12 cm). Therefore, Bonner spheres with a diameter larger than 12 cm cannot be used for Bonner sphere spectrometry, which makes them difficult to use for measuring BNCT neutron flux, unlike general measurements.

[0005] There are two points to consider when designing a high-performance neutron spectrometer using a moderator. First, the neutron energies to be measured usually span a very wide energy range, so the neutron spectrometer must operate in the meV to tens of MeV range and accurately measure the neutron energy spectrum. Second, because there are no detectors that can simultaneously measure a very wide neutron energy range, the neutron count rate must be measured using moderators of various sizes, and the reactivity depending on the energy must be carefully calculated.

[0006] Furthermore, neutron spectrometers that use moderators are basically designed to slow down neutrons and convert them into thermal neutrons, and then measure them with a thermal neutron detector inserted inside. In order to slow down neutrons with a neutron energy of 1 MeV or more, a polyethylene moderator of 10 cm or more is usually used to reach the thermal neutron detector, which poses the problem that the neutron spectrometers based on moderators are heavy, weighing more than 50 kg. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been derived to solve the above-mentioned problems of the prior art, and relates to a neutron detector that measures a neutron energy spectrum over a wide energy range from thermal neutrons to fast neutrons. [Means for solving the problem]

[0008] The device includes a sensor for detecting neutrons, a detection unit including a moderator provided around the sensor, and a moving unit for moving the detection unit or the sensor, wherein the moving unit moves the moderator or sensor of the detection unit, thereby fixing the sensor or the moderator at a preset position and varying the relative position of the moderator with respect to the sensor. [Effects of the Invention]

[0009] The neutron detector of the present invention is configured such that the sensor is fixed at a predetermined position in the moderator, and the moderator is moved or the sensor is moved within the fixed moderator, and the relative position of the moderator to the sensor is variable, and has the effect of being able to detect neutrons with a wide range of energies, from thermal neutrons with energies of 0.025 eV or less that are incident from a specific direction to fast neutrons with energies greater than 1 MeV.

[0010] In addition, the neutron detector of the present invention is configured in a form in which a number of cylindrical structures are concentrically stacked in the axial direction, and the diameter of each cylindrical structure decreases from the rear to the front along the axial direction, thereby having the effect of being able to detect neutrons having a wide range of energies from high to low.

[0011] In addition, the neutron detector of the present invention has a sensor scintillator made of LiCAF, and has a scintillation rate of 1 × 10 9 cm -2 s -1 This has the effect of making it possible to measure the above-mentioned flux. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows conventional Bonner sphere spectrometer photographs with various sizes and reaction functions with neutron energy. [Figure 2] Schematic diagram of boron neutron capture therapy (BNCT). [Figure 3] This is a conceptual diagram of thermal neutrons elastically scattering with a moderator and reaching a thermal neutron detector. [Figure 4] This is a photo of a conventional Bonner sphere with a polyethylene moderator and metal skin. [Figure 5] FIG. 1 is a schematic diagram of a conventional long counter measuring device. [Figure 6] FIG. 2 is a schematic diagram showing the inside of the neutron detector of the present invention. [Figure 7] 1 is a schematic diagram of a neutron detector of the present invention. [Figure 8]1 is a schematic diagram of a moderator of the present invention. [Figure 9] 1 is a schematic diagram showing the inside of a moderator according to the present invention; [Figure 10] FIG. 2 is a cross-sectional view of the inside of a detection unit of the present invention. [Figure 11] 3 is a schematic diagram of a sensor provided in a detection unit of the present invention. FIG. [Figure 12] 1 is an actual photograph of a sensor provided in a detection unit of the present invention. [Figure 13] 1 is a graph showing a response function according to the position of a sensor provided inside the moderator of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The neutron detector of the present invention includes a sensor for detecting neutrons, a detection unit including a moderator provided around the sensor, and a moving unit for moving the detection unit, wherein the moving unit moves the moderator of the detection unit or the sensor, thereby fixing the sensor or the moderator at a predetermined position and varying the relative position of the moderator with respect to the sensor.

[0014] The moderator is formed in a structure in which the center of the moderator is penetrated in the axial direction, and the sensor is disposed in the hollow of the moderator.

[0015] The moderator is configured in a form in which a number of cylindrical structures are concentrically stacked in the axial direction, and the diameter of each cylindrical structure decreases from rear to front along the axial direction.

[0016] The detection unit further includes a reference sensor.

[0017] The moderator further includes a blocking cap for blocking the hollow of the moderator.

[0018] The moving unit is configured to move the detecting unit in forward and backward directions.

[0019] The detection unit further includes an inner moderator surrounding an outer circumferential surface of the moderator.

[0020] The detection unit further includes a cover surrounding an outer circumferential surface of the inner moderator.

[0021] The moderator may be made of any one of polystyrene, polyethylene, and boron-containing polyethylene.

[0022] The sensor is 1×10 9 cm -2 s -1 The above-mentioned flux measurement is possible.

[0023] MODE FOR CARRYING OUT THE INVENTION The present invention relates to a neutron flux measurement device that measures the neutron energy spectrum in a wide energy range from thermal neutrons to fast neutrons generated in boron neutron capture therapy. Fig. 2 is a diagram illustrating a schematic diagram of boron neutron capture therapy (BNCT). Referring to Fig. 2, (1) a proton beam is incident on a Be (beryllium) target, (2) neutrons are generated, (3) the neutrons are incident on cancer cells that have been injected with drug-treated boron, and (4) 10 B(n, α) 7 Li nuclear reaction occurs, and the charged particles produced during this reaction are (5) α particles and 7 The kinetic energy of Li is transferred to cancer cells, killing them. In order for BNCT to treat cancer cells, sufficient epithermal neutrons (0.5 eV to 10 keV) must be generated so that the neutron energy reaches the cancer cells.

[0024] Also, referring to Figure 2, in the case of BNCT, the direction of neutron incidence is fixed so that the treatment area of ​​the patient to be irradiated with neutrons is closely attached to the beam output port of the BNCT treatment chamber. Unlike a general Bonner sphere spectrometer that must consider all incident directions, the BNCT neutron spectrometer targets neutron beams incident from one direction.

[0025] The requirements for BNCT treatment facilities stated in the IAEAL 23-01601 technical document (Advances in Boron Neutron Capture Therapy) are that the epithermal neutron (0.5 eV - 10 keV) flux is 5 × 10 8 cm -2 s -1 The thermal neutron / epithermal neutron ratio must be 0.05 or less, and there must be no fluctuation in the neutron flux and energy distribution during treatment. The Bonner sphere spectrometer for detecting neutrons can measure neutrons with various energies, from thermal neutrons to fast neutrons, and low-energy thermal neutrons can be measured, but as shown in Figure 3, high-energy thermal neutrons must undergo elastic scattering with the hydrogen that makes up the moderator 130 inside the Bonner sphere in order to reach the thermal neutron detector, making it possible to determine the energy distribution.

[0026] Therefore, various sizes of Bonner spheres are required to moderate high-energy neutrons. When measuring neutrons of 100 MeV or more, as shown in Figure 4, a polyethylene moderator and metal shell are used to expand the measurement range to 1 GeV or more, making it possible to measure neutrons with energies of 1 GeV or more. Therefore, in order to measure neutrons with various energy distributions, Bonner sphere spectrometers must use various sizes of Bonner spheres, which results in long measurement times and complexity.

[0027] Figure 5 is a schematic diagram of a conventional long counter measurement device. Another method of detecting neutrons besides the Bonner sphere spectrometer mentioned above is to use a long counter measurement device. A long counter measurement device allows neutrons to be incident in only one direction, and can measure neutron energy when the neutron position and target cancer cell are known in advance. However, there is a problem in that it is not possible to measure various neutron energy distributions.

[0028] As mentioned above, BNCT equipment can measure the energy of neutrons emitted from the beam port using a Bonner sphere spectrometer and a long counter measurement device. However, the Bonner sphere spectrometer must be changed in size to measure various neutron energies, and the long counter measurement device can only measure the energy of neutrons incident from one direction.

[0029] Therefore, in the present invention, a Bonner sphere spectrometer and a long counter measurement device are combined to obtain a 1 × 10 9 cm -2 s -1 The neutron detector 1000 capable of detecting neutrons from different positions so as to enable the above-described flux measurement and simultaneous measurement of the entire energy range will be described in more detail with reference to specific examples or embodiments including the accompanying drawings. However, the following specific examples or embodiments are merely references for describing the present invention in detail, and the present invention is not limited thereto and can be realized in various forms.

[0030] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The terms used for the purpose of description in this specification are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0031] Also, as used in the specification and the appended claims, the singular forms "a," "an," and "the" can be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0032] Furthermore, when a part is described as "comprising" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified to the contrary.

[0033] 6 is a diagram illustrating a schematic internal view of a neutron detector according to the present invention. Referring to FIG. 6, a neutron detector 1000 according to the present invention includes a sensor 120, a detection unit 100, and a moving unit 200. The sensor 120 is for detecting neutrons and includes a moderator 130 provided around the sensor 120. The moderator 130 has a structure in which its center is axially penetrated, and the sensor 120 is disposed in the hollow of the moderator 130. The detection unit 100 further includes a reference sensor 121.

[0034] 7 is a schematic diagram of a neutron detector according to the present invention. Referring to FIG. 7, the detection unit 100 is coupled to the moving unit 200, and the moving unit 200 moves the detection unit 100 or the sensor 120. Specifically, the moving unit 200 moves the moderator 130 or the sensor 120 of the detection unit 100. Thus, the sensor 120 or the moderator 130 is fixed at a predetermined position, and the relative position of the moderator 130 with respect to the sensor 120 is variable. The moving unit 200 may be formed of an actuator that can be driven by a motor, and the detection unit 100 can be moved forward and backward by the actuator. Therefore, while the sensor 120 is fixed, the position of the moderator 130 inside the detection unit 100 can be measured by moving the moving unit 200, and neutrons with various energies, from thermal neutrons with energies of 0.025 eV or less incident from a specific direction to fast neutrons with energies greater than 1 MeV, can be detected.

[0035] 8 is a schematic diagram of a moderator according to the present invention. Referring to FIG. 8, the moderator 130 according to the present invention is configured in the form of a plurality of cylindrical structures concentrically stacked in the axial direction, with the diameter of each cylindrical structure decreasing from rear to front along the axial direction. The moderator 130 may include a plurality of cylindrical structures, each with a diameter decreasing from rear to front, enabling detection of neutrons with a range of energies. Specifically, the moderator 130 is configured as a cylindrical structure and includes a cylindrical first moderator 131, a second moderator 132 having a diameter smaller than that of the first moderator 131 and formed inside side walls defining one and the other sides of the first moderator 131, a third moderator 133 having a diameter smaller than that of the second moderator 132 and formed on one side of the second moderator 132, and a fourth moderator 134 having a diameter smaller than that of the third moderator 133 and formed on one side of the third moderator 133. In the conventional neutron detection method using Bonner spheres, a large diameter Bonner sphere must be used to increase the reactivity of neutrons in order to detect high-energy neutrons, and a small diameter Bonner sphere must be used to detect low-energy neutrons. Therefore, in order to measure reactivity using Bonner spheres from the thermal neutron region to the fast neutron region, Bonner spheres with high reactivity must be used for each neutron region. However, in the neutron detector 1000 of the present invention, the neutron detecting sensor 120 is configured to move within the detection unit 100, which is composed of moderators 130 of various sizes, so that neutrons of various energies can be easily and quickly detected using only the neutron detector 1000 of the present invention.

[0036] The cylindrical structure is configured in an axially stacked configuration of a first moderator, a second moderator, a third moderator 133, and a fourth moderator 134, with the moderator 130 being made of one of polystyrene, polyethylene, and boron-doped polyethylene. The moderator 130 serves to moderate incident neutrons and convert them into thermal neutrons. Here, polyethylene, polystyrene, and boron-doped polyethylene can moderate neutrons. Polystyrene has the structural formula (CH)n, and polyethylene has the structural formula (CH2)n. The more hydrogen there is, the more neutrons lose energy due to elastic scattering between neutrons and hydrogen, and are converted into thermal neutrons. Therefore, polyethylene has a higher neutron moderation effect than polystyrene. Therefore, the first moderator 131 of the neutron detector 1000 of the present invention is made of polyethylene (PE). Since the first moderator 131 is made of polyethylene, which has high neutron moderation efficiency, it can effectively moderate high-energy fast neutrons. In addition, the second moderator 132, the third moderator 133, and the fourth moderator 134 are made of polystyrene (PS). By making the second moderator 132, the third moderator 133, and the fourth moderator 134 out of polystyrene, it is possible to moderate low-energy slow neutrons and prevent excessive moderation of neutrons. In addition, the outer peripheral surface of the fourth moderator 134 is made of polyethylene containing boron. Here, boron can serve to capture and remove thermal neutrons, and since the outer peripheral surface of the fourth moderator 134 is made of polyethylene containing boron, it is possible to block thermal neutrons from directly penetrating into the sensor 120 that detects neutrons.

[0037] FIG. 9 is a schematic diagram illustrating the interior of a moderator according to the present invention. Referring to FIG. 9, the moderator 130 includes an inner moderator 111 surrounding the outer periphery of the moderator 130, and the inner moderator 111 further includes a cover 110 surrounding the outer periphery of the inner moderator 111. The outer periphery of the inner moderator 111, which abuts against the first moderator 131, is made of boron-containing polyethylene. The inner moderator 111 is made of boron-containing polyethylene, which can block thermal neutrons entering from the outside. Boron-containing polyethylene has the property of removing moderated thermal neutrons, which can prevent thermal neutrons from entering the moderator 130 and separate the neutron detection area according to neutron energy. The cover 110 can also be made of aluminum. The aluminum cover 110 serves to protect the inner moderator 111. Specifically, this is to obtain accurate and reliable results by blocking neutrons incident from undesired directions among neutrons incident from outside.

[0038] 10 is a view illustrating an internal cross section of the detection unit 100 of the present invention. Referring to FIG. 10, the detection unit 100 of the present invention includes a cover 110, an inner moderator 111, and a moderator 130 provided in the inner moderator, and the moderator 130 has a hollow formed therein through which the sensor 120 passes. In addition, a reference sensor 121 may be further provided inside the moderator 130, and a blocking cap 135 may be further provided to block the hollow formed inside the moderator 130. The moderator 130 has a plurality of cylindrical structures and is configured in a shape in which the diameter decreases from the rear to the front. The reactor is made up of a first moderator 131, a second moderator 132 that is smaller in diameter than the first moderator 131 and is formed inside the side walls that form one side and the other side of the first moderator 131, a third moderator 133 that is smaller in diameter than the second moderator 132 and is formed on one side of the second moderator 132, and a fourth moderator 134 that is smaller in diameter than the third moderator 133 and is formed on one side of the third moderator 133. The moderator 130 serves to moderate incident neutrons and convert them into thermal neutrons, and is made of one of polystyrene, polyethylene, or boron-doped polyethylene. Polystyrene has the structural formula (CH)n, and polyethylene has the structural formula (CH2)n, so it contains hydrogen atoms. Neutrons lose energy through elastic scattering between neutrons and hydrogen, converting them into thermal neutrons, thereby moderating the neutrons.

[0039] Fig. 11 is a schematic diagram of a sensor provided in the detection unit 100 of the present invention, and Fig. 12 is an actual photograph of the sensor provided in the detection unit of the present invention. Referring to Fig. 11(a), a central sensor 120 of the present invention includes a scintillator made of LiCA and a blocking cap 20 made of boron carbide. Also, referring to Fig. 11(b), a reference sensor 121 of the present invention includes a scintillator made of LiCA and a blocking cap 30 made of boron carbide.

[0040] The blocking caps 20 and 30 in Fig. 11 may be configured to block the hollow of the moderator 130, and the boron contained in the blocking caps 20 and 30 can block thermal neutrons moderated by the moderator 130 from reaching the central sensor 120 and the reference sensor 121. When the blocking caps 20 and 30 are used, the thermal neutron reactivity of the central sensor 120 and the reference sensor 121 can be reduced to 1 / 10 or less compared to when the blocking caps 20 and 30 are not used. Therefore, the present invention is applicable to a case where the epithermal neutron (10 eV to 10 keV) flux is 1 x 10 9 cm -2 s -1 Neutron measurement is possible even in a high flux environment.

[0041] The scintillator of the sensor 120 in (a) of Fig. 11 is made of LiCAF. Here, the requirement of a BNCT treatment facility is that the epithermal neutron (10 eV to 10 keV) flux is 1 × 10 9 cm -2 s -1 Since the scintillator of the sensor 120 is made of LiCAF, the 9 cm -2 s -1 The above-described effect is achieved by enabling measurement of the radiation flux. In addition, the sensor 120 is configured to be connected to an optical fiber, and a signal of neutrons detected by the sensor 120 can be extracted. The extracted signal can be output to an external signal processing device, and neutron energy can be calculated based on the number of counted neutrons. As shown in FIG. 11(b), the detector further includes a reference sensor 121 in addition to the sensor 120. The reference sensor 121 is configured by fixing the sensor 120 to a position on the moderator 130 that is different from a preset position. The reference sensor 121 serves to monitor and correct the measured value of neutrons detected and counted by the sensor 120. Therefore, the reference sensor 121 allows correction of the count value of neutrons detected by the sensor 120 in real time, thereby obtaining an accurate count value.

[0042] Figure 13 is a graph showing a response function graph according to the position of a sensor provided inside the moderator of the present invention, and is a graph showing the response function of neutrons when the sensor 120 of the present invention is moved to various positions inside the moderator 130. Referring to Figure 12, it is possible to obtain a difference in reactivity depending on the size of the moderator, as in the Bonner sphere spectrometer of Figure 1(b).

[0043] The present invention is not limited to the above-described embodiments, and it goes without saying that the scope of application is varied, and that various modifications can be made without departing from the gist of the present invention as claimed in the claims. [Industrial Applicability]

[0044] The present invention relates to a neutron detector that can measure the neutron energy spectrum over a wide energy range from neutrons to fast neutrons, and is capable of detecting neutrons with a wide range of energies, from thermal neutrons with energies of 0.025 eV or less that are incident from a specific direction to fast neutrons with energies greater than 1 MeV.

Claims

1. a detection unit including a sensor for detecting neutrons and a moderator provided around the sensor; a moving unit that moves the detection unit or the sensor, the moving unit moves a moderator or a sensor of the detection unit, This allows the relative position of the moderator with respect to the sensor to be varied, thereby providing a neutron detector.

2. The moderator is The neutron detector according to claim 1 , wherein the moderator has a structure penetrating the center in the axial direction, and the sensor is disposed in the hollow of the moderator.

3. The moderator is 3. The neutron detector according to claim 2, wherein a plurality of cylindrical structures are stacked concentrically in the axial direction, and the diameter of each cylindrical structure decreases from rear to front along the axial direction.

4. The detection unit The neutron detector of claim 1 further comprising a reference sensor.

5. The moderator is The neutron detector of claim 2 further comprising a blocking cap that blocks the hollow moderator.

6. The moving unit is The neutron detector according to claim 1 , wherein the detection unit is moved forward and backward.

7. The detection unit The neutron detector of claim 1 further comprising an inner moderator surrounding an outer periphery of the moderator.

8. The detection unit The neutron detector of claim 7 , further comprising a cover surrounding an outer periphery of the inner moderator.

9. The moderator is 4. The neutron detector of claim 3, wherein the moderator is made of one of polystyrene, polyethylene, and boron-doped polyethylene.

10. The sensor is 1 x 10 ９ cm －２ s －１ 2. The neutron detector according to claim 1, wherein the above-mentioned flux measurements are possible.

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