Neutron detector

Abstract

To solve the problem in which, in conventional neutron detectors, a peak value of a pulse signal, which is an output signal of the detector, differed depending on whether an incident position of a neutron was near both ends or the center of a scintillator, that is, the peak value when the incident position is near both ends of the scintillator was smaller than the peak value when the incident position is near the center of the scintillator.SOLUTION: A neutron detector comprises: a housing 3; a detection unit 1 including a neutron scintillator 14 provided inside the housing, composed of a ZnS phosphor and a neutron converter including 6 Li or 10B, and emitting fluorescent light when a neutron is detected, a photomultiplier tube 5 provided inside the housing and detecting fluorescent light from the neutron scintillator, a light guide 15 provided inside the housing, supporting the neutron scintillator by optical bonding, and guiding fluorescent light from the neutron scintillator to the photomultiplier tube, and a reflective material 13 provided inside the housing and surrounding the periphery of the light guide; and a signal processing unit 2 provided outside the detection unit and taking out a signal from the photomultiplier tube as a detection signal of a neutron.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This application relates to neutron detectors. [Background technology]

[0002] Conventionally, neutron detectors used for power output monitoring or criticality detection in nuclear power plants or nuclear fuel reprocessing plants have included BF3 counters or 3 Gas-filled detectors such as He proportional counters have been used for their gamma-ray discrimination properties, wide operating range, and long-term stability.

[0003] Among gas-filled detectors 3 He proportional counters are the most widely used neutron detectors due to their excellent detection sensitivity and the highest sensitivity for thermal neutrons. 3 Helium gas is currently difficult to obtain worldwide, and it may become unavailable in the near future. 3 The development of neutron detectors to replace He gas is being undertaken worldwide, and among these, the most promising alternative detector is one that uses a scintillator.

[0004] 3 As a neutron detector using a scintillator as a detection medium instead of He gas, n S phosphor and 6 Li or 10 A plate-shaped semi-transparent neutron scintillator that is made up of a neutron converter containing B and has a structure that allows fluorescence to be emitted from both sides is placed inside the detector housing, and when neutrons are incident on this scintillator, the emitted fluorescence is detected by a photomultiplier tube placed on one end of the semi-transparent neutron scintillator, and the signal output from this photomultiplier tube is processed and extracted as a neutron signal (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-20860 A (Figs. 1, 2, and 3) Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional 3 A neutron detector using a scintillator as a detection medium instead of He gas is configured as described above, and since the photomultiplier tubes arranged at both ends of the plate-shaped scintillator have different light collection rates for the scintillation light generated by interaction with neutrons, the peak value of the pulse signal obtained as the detector output signal differs between when a neutron is incident near both ends of the scintillator, which is close to the photomultiplier tube, and when the neutron is incident near the center of the scintillator, away from the photomultiplier tube, and the pulse peak value when a neutron is incident near the center of the scintillator is smaller than when the neutron is incident near both ends of the scintillator.

[0007] In neutron detectors that use scintillators, the pulse signals generated by interactions with gamma rays become noise signals, so a pulse height discrimination level is set to distinguish between pulse signals due to neutrons and pulse signals due to gamma rays.

[0008] Here, since the pulse height value due to neutrons is greater than the pulse height value due to gamma rays, pulse signals with pulse height values ​​below the set pulse height discrimination level are regarded as pulse signals due to gamma rays and are not counted in the downstream counting circuit. However, in the case of a plate-shaped scintillator, if the pulse height value when a neutron is incident near the center is lower than the pulse height discrimination level, it is not processed as a signal due to a neutron, resulting in low counting efficiency.

[0009] Furthermore, in the case of conventional gas-filled detectors, the sensitive area of ​​the detector is filled with gas, so the directionality of the detector is not an issue. However, in the case of detectors that use plate-shaped scintillators, there is a problem in that the detection sensitivity differs depending on whether neutrons are incident on the plate-shaped scintillator from the front or the side.

[0010] moreover, 3 In the case of using it as an alternative detector for He gas, the following have been actually applied in nuclear power plants and nuclear fuel reprocessing plants: 3 Since it is necessary to be able to handle periodic replacement of He proportional counters, 3 The external dimensions are the same as or smaller than those of a He proportional counter. 3 There is a constraint that the detection sensitivity must be equal to or greater than that of a He proportional counter.

[0011] The present application discloses a technique for solving the above problems, 3 Without using He gas, 3 The objective is to obtain a small neutron detector with high neutron detection efficiency that can replace the He proportional counter. [Means for solving the problem]

[0012] The neutron detector disclosed in the present application comprises: A housing and A ZnS phosphor is provided inside the housing. 6 Li or 10 The neutron scintillator is made up of a neutron converter containing B, which emits fluorescence when it detects neutrons, and a photomultiplier tube provided inside the housing for detecting the fluorescence from the neutron scintillator; a light guide provided inside the housing, supporting the neutron scintillator by optical bonding and guiding fluorescence from the neutron scintillator to the photomultiplier tube; The light guide is provided inside the housing. and the neutron scintillator Surrounding the Of light Reflective material; A detection unit having a signal processing unit provided outside the detection unit and configured to extract a signal from the photomultiplier tube as a neutron detection signal; Equipped with It is characterized by the above. Effect of the Invention

[0013] According to the neutron detector disclosed in the present application, 3 Without using He gas, 3 It is possible to obtain a small neutron detector with high neutron detection efficiency that can replace a He proportional counter. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an example of a neutron detector according to a first embodiment. [Diagram 2] FIG. 4 is a diagram showing an example of a measurement result measured by the neutron detector according to the first embodiment. [Diagram 3] FIG. 11 is a diagram showing an example of a neutron detector according to a second embodiment. [Figure 4] FIG. 11 is a diagram showing an example of a neutron detector according to a third embodiment. [Diagram 5] FIG. 13 is a diagram showing an example of a neutron detector according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present application relates to a radiation detector that measures a radiation dose rate in a measurement target field in a high radiation exposure environment such as a nuclear power plant or a nuclear fuel reprocessing plant, and in particular to a neutron detector using a scintillator.

[0016] Embodiment 1 Fig. 1 is a diagram showing an example of the configuration of a neutron detector according to embodiment 1. In Fig. 1, the neutron detector is composed of a detection unit 1 and a signal processing unit 2. In Fig. 1, Fig. 1(a) is a schematic configuration diagram showing the entire neutron detector according to embodiment 1, and Fig. 1(b) is a cross-sectional view showing a cross-section of the center of a scintillator (see dashed dotted line AA in Fig. 1(a)) of the detection unit 1, which will be described in detail below.

[0017] The detection unit 1 has a structure in which a scintillator unit 4 that reacts to neutrons and emits light, a photomultiplier tube 5, and a photomultiplier tube bleeder circuit 6 are incorporated into a detector housing 3 (hereinafter simply referred to as "housing 3") that has light-shielding and electromagnetic shielding effects.

[0018] The scintillator section 4 is provided on the side surface of the rectangular light guide 15. 6 Li or 10 A neutron scintillator 14 containing B is attached by optical bonding, and the periphery is covered with a reflecting material 13. The reflecting material 13 may be white paint or a fluororesin tape.

[0019] The signal processing unit 2 is composed of an amplifier circuit 7 that amplifies the output charge, which is the signal from the detection unit 1, a pulse height discrimination circuit 8 that discriminates neutron pulses from noise or gamma ray pulses, a waveform shaping circuit 9 that shapes the output waveform into a rectangular wave, a counter 10 that counts the number of pulses, and a high-voltage power supply 11 that supplies a high voltage to the detection unit 1.

[0020] When a neutron beam (neutrons) enters the detection section 1, light is emitted from the neutron scintillator 14, and the light is efficiently reflected inside the scintillator section 4 by the reflector 13 and light guide 15, and transmitted to the photomultiplier tube 5, which is expected to improve sensitivity.

[0021] FIG. 2 shows the results of measuring the irradiation position dependency of the count rate related to neutron detection by the neutron detector in order to confirm the detection performance of the neutron detector according to the first embodiment. Two types of detectors were prepared: one with a light guide 15 and one without a light guide 15. The count rate of the neutron detector according to embodiment 1 was measured for each detector while changing the position at which radiation was irradiated.

[0022] The source of radiation is 60 Co was used and collimated to a width of 5 mm and irradiated from the side of the detector. As a result, at the center position of the detector (approximately 45 mm away from the photomultiplier tube), the count rate measurement result with the detector with a light guide was approximately five times higher than the count rate measurement result with the detector without a light guide, and near the tip of the detector (80 mm from the photomultiplier tube), the detector with a light guide showed an approximately eight-fold improvement in sensitivity compared to the detector without a light guide.

[0023] The light guide is made of acrylic and is 10 mm x 10 mm x 92 mm in size. The neutron scintillator is 6 A Li-containing glass scintillator (6.6 mm × 90 mm × t1.3 mm) was used.

[0024] Embodiment 2 Next, a neutron detector according to embodiment 2 will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the configuration of a neutron detector according to embodiment 2. In Fig. 3, the neutron detector is also composed of a detection section 1 and a signal processing section 2. The features of the neutron detector according to embodiment 2 will be described in detail below, focusing on the differences from embodiment 1. In Fig. 3, Fig. 3(a) is a schematic configuration diagram showing the entire neutron detector according to embodiment 2, and Fig. 3(b) is a cross-sectional view showing a cross-section of the center of the scintillator section 4 of the detection section 1 (see dashed line BB in Fig. 3(a)).

[0025] In the neutron detector of embodiment 1 above, a structure has been described in which neutron scintillator 14 is bonded to one of the side surfaces of light guide 15. However, in the neutron detector of embodiment 2, as shown in FIG. 3, a structure has neutron scintillators 141, 142, 143, and 144 bonded to four of the side surfaces of light guide 15, so that further improvement in sensitivity can be expected compared to the neutron detector of embodiment 1.

[0026] In addition, the neutron detector of embodiment 1 has the drawback of providing high sensitivity to neutrons incident perpendicularly to the surface of the neutron scintillator, but reducing sensitivity to neutrons incident horizontally. However, the neutron detector of embodiment 2 provides uniform sensitivity in all circumferential directions, and is expected to provide improved directional characteristics.

[0027] Embodiment 3 Next, a neutron detector according to embodiment 3 will be described with reference to Fig. 4. Fig. 4 is a diagram showing an example of the configuration of a neutron detector according to embodiment 3. In Fig. 4, the neutron detector is also composed of a detection section 1 and a signal processing section 2. The features of the neutron detector according to embodiment 3 will be described in detail below, focusing on the differences from embodiments 1 and 2. In Fig. 4, Fig. 4(a) is a schematic configuration diagram showing the entire neutron detector according to embodiment 3, and Fig. 4(b) is a cross-sectional view showing a cross-section of the center of the scintillator section 4 of the detection section 1 (see dashed line CC in Fig. 4(a)).

[0028] The neutron detectors according to the above-mentioned embodiments 1 and 2 have a structure in which a photomultiplier tube 5 is combined with one end face of the scintillator section 4, but the neutron detector according to embodiment 3 is significantly different in structure in that it has photomultiplier tubes 51, 52 on both end faces of the scintillator section 4 as shown in Fig. 4. And, by combining these photomultiplier tubes 51, 52 in the neutron detector according to embodiment 3, further improvement in sensitivity can be expected.

[0029] That is, as shown in FIG. 4, photomultiplier tube 51 is combined with a photomultiplier tube bleeder circuit 61, an amplifier circuit 71 that amplifies electric charge, and a high-voltage power supply 111, while photomultiplier tube 52 is combined with a photomultiplier tube bleeder circuit 62, an amplifier circuit 72 that amplifies electric charge, and a high-voltage power supply 112.

[0030] In addition, the amplifier circuit 71, which amplifies the charge output through the photomultiplier tube 51 of the detection unit 1, is connected to a pulse-height discrimination circuit 81 that discriminates neutron pulses from noise or gamma ray pulses, a waveform shaping circuit 91 that shapes the output waveform into a square wave, and a counter 101 that counts the number of pulses. The amplifier circuit 72, which amplifies the charge output through the photomultiplier tube 52 of the detection unit 1, is connected to a pulse-height discrimination circuit 82 that discriminates neutron pulses from noise or gamma ray pulses, a waveform shaping circuit 92 that shapes the output waveform into a square wave, and a counter 102 that counts the number of pulses.

[0031] In other words, the neutron detector of embodiment 1 has a light guide, and therefore has higher sensitivity than one without a light guide, as shown in Figure 2, but has the disadvantage of having low sensitivity for reactions far from the photomultiplier tube (the same is true for the neutron detector of embodiment 2).

[0032] In contrast, the neutron detector according to embodiment 3 has photomultiplier tubes 51, 52 combined with both end faces of the scintillator section 4 as described above, and is therefore characterized in that high sensitivity can be obtained at both ends.

[0033] Embodiment 4 Next, a neutron detector according to the fourth embodiment will be described with reference to FIG. 5. FIG. 5 is a diagram showing an example of the configuration of the neutron detector according to the fourth embodiment. In FIG. 5, the neutron detector is also composed of a detection unit 1 and a signal processing unit 2, as in the above-mentioned first to third embodiments. Also, as in the neutron detector according to the third embodiment, the neutron detector has photomultiplier tubes 51 and 52 on both end faces of the scintillator unit 4. Therefore, the features of the neutron detector according to the fourth embodiment will be described in detail below, focusing on the differences from the third embodiment. In FIG. 5, FIG. 5(a) is a schematic configuration diagram showing the entire neutron detector according to the fourth embodiment, and FIG. 5(b) is a cross-sectional view showing a cross section of the center of the scintillator unit 4 of the detection unit 1 (see the dashed line DD in FIG. 5(a)).

[0034] In the neutron detector according to the third embodiment, a structure in which output is provided from both ends of the detection unit 1 has been described above, but when measuring the inside of a pipe, etc., the detector output may only be obtained from one side. Even in such a case, as shown in Fig. 5, by folding back the wiring on the tip side of the detector, storing it inside the housing 3, and drawing it out from one side, it is possible to obtain a neutron detector according to the fourth embodiment, which has an even wider range of application than the neutron detector according to the third embodiment.

[0035] Furthermore, since the neutron detector of embodiment 4 employs the structure described above, even if it has photomultiplier tubes 51, 52 on both end faces of the scintillator section 4, only one high-voltage power supply 113 is required to supply voltage to the detection section 1, and not two as in embodiment 3 (see Figure 5).

[0036] Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not exemplified are assumed within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0037] 1 detection section, 2 signal processing section, 3 housing (detector housing), 4 scintillator section, 5, 51, 52 photomultiplier tube, 6, 61, 62 photomultiplier tube bleeder circuit, 7, 71, 72 amplifier circuit, 8, 81, 82 pulse height discrimination circuit, 9, 91, 92 waveform shaping circuit, 10, 101, 102 counter, 11, 111, 112, 113 high voltage power supply, 13 reflector, 14, 141, 142, 143, 144 neutron scintillator, 15 light guide

Claims

1. A housing and A ZnS phosphor is provided inside the housing. 6 Li or 10 A neutron scintillator that is composed of a neutron converter containing B and emits fluorescence when it detects neutrons; a photomultiplier tube provided inside the housing for detecting the fluorescence from the neutron scintillator; a light guide provided inside the housing, supporting the neutron scintillator by optical bonding and guiding fluorescence from the neutron scintillator to the photomultiplier tube; a light reflecting material provided inside the housing and surrounding the light guide and the neutron scintillator; A detection unit having a signal processing unit provided outside the detection unit and configured to extract a signal from the photomultiplier tube as a neutron detection signal; Equipped with A neutron detector comprising:

2. 2. The neutron detector according to claim 1, wherein the neutron scintillator is configured in a plate shape, the light guide is configured in a rectangular prism shape, and the plate-shaped neutron scintillator is optically joined to all side surfaces of the light guide.

3. 3. The neutron detector according to claim 1, wherein the photomultiplier tubes are disposed on both ends of the neutron scintillator in the longitudinal direction.

4. The neutron detector according to claim 3, characterized in that, of the output terminals of the detection section provided on both sides of the longitudinal ends of the detection section, the terminal on one side is structured to be pulled out to the outside of the detection section together with the terminal on the other side.

Images