CN111045073B

CN111045073B - Detector capable of simultaneously measuring low-energy neutrons and high-energy neutrons

Info

Publication number: CN111045073B
Application number: CN201911260685.2A
Authority: CN
Inventors: 张显鹏; 田耕; 何世熠; 张忠兵; 陈亮
Original assignee: Northwest Institute of Nuclear Technology
Current assignee: Northwest Institute of Nuclear Technology
Priority date: 2019-12-10
Filing date: 2019-12-10
Publication date: 2021-08-31
Anticipated expiration: 2039-12-10
Also published as: CN111045073A

Abstract

The invention belongs to the field of neutron detection, and particularly relates to a detector capable of simultaneously measuring low-energy neutrons and high-energy neutrons. The defect that the conventional neutron detector can only measure high-energy neutrons is overcome, the detection characteristic of the novel CLYC scintillator on low-energy neutrons and good n-gamma discrimination capability are utilized, and the novel sandwich type neutron detector is provided. CLYC crystals and organic scintillators with n-gamma discrimination are used as detection media, and different particles are discriminated by using different light-emitting times and a pulse shape discrimination method. Low-energy neutrons and high-energy neutrons can be measured simultaneously. Meanwhile, the device has the capability of removing gamma photons, protons and electrons, and has the advantages of miniaturization, simple structure and the like.

Description

Detector capable of simultaneously measuring low-energy neutrons and high-energy neutrons

Technical Field

The invention belongs to the field of neutron detection, and particularly relates to a detector capable of simultaneously measuring low-energy neutrons and high-energy neutrons.

Background

With the development of aerospace technology, especially manned aerospace technology, the measurement of space radiation environment is urgently needed. The space radiation environment is very complex, and only in a near earth orbit (LEO), a plurality of radiation particles including protons, neutrons, electrons, heavy ions, X-rays, gamma-rays and the like are distributed. Among these particles, neutrons are mostly secondary neutrons generated by interaction of energetic primary particles with nuclei of the spacecraft's own material. Their energy ranges from thermal neutrons to several gevs. On the near earth orbit, the influence of the Galaxy Cosmic Rays (GCRs) is small, so that the energy of neutrons is mostly below 200 MeV. The hazards of neutrons are mainly manifested as: (1) neutrons are even far more damaging to astronauts than to materials. Because neutrons are uncharged, the penetration force to human tissues is very strong, and therefore, internal tissues or cells of the human body are more easily diseased. In an International Space Station (ISS) type orbit, the contribution range of neutrons to the total dose equivalent of astronauts is estimated to be between 30% and 60%, and the quality factor of the orbit is about 4 to 5 times that of charged particles; (2) neutrons are the most main factors for inducing the electronic device to generate single event effect in the near space, and form extra charges through direct or indirect ionization in the device material, so that the problems of single event effect, displacement damage and the like are caused, and the precision, the service life and the normal operation of the instrument are directly influenced.

Therefore, the spatial neutron detection has extremely important significance in the aspects of personnel safety of manned and spaceflight, the aspects of exploration of space environment and resources, and research in the fields of space physics, astronomical observation, life exploration and the like.

A sandwich detector consisting of scintillators with different decay times or different types of detected particles is a more common active detector, e.g. NE102A + csi (tl), NE115+ NE102A, BC454+ BGO, etc. In the nineties of the last century, M.Takada et al, Japan, developed a sandwich scintillator neutron detector for the resolution of neutrons in complex charged particle fields, which was able to detect neutrons with energies below 130MeV, reference M.Takada, S.Taniguchi, et al, neutron spectrometry in a mixed field of neutrons and protons with a photoswitch neutron detector, Nuclear Instruments and Methods in Physics Research A465: 511 (2001).

A typical structure is shown in fig. 1, the middle shaded part is a liquid scintillator NE213 (same as the current EJ-301) 11 with n-gamma discrimination capability, which emits light faster and has a decay time of 3.2 ns; while the plastic scintillator NE115 (same as the current EJ-240) 12, around which the middle scintillator is "wrapped", emits light slower with a decay time of 225 ns; the luminescence of both scintillators is coupled into a photomultiplier tube. The detection result of the detector in the mixed field test is shown in fig. 2, and the regions corresponding to different rays can be clearly distinguished from the figure: gamma-rays are the a region, which has only one fast component; neutrons correspond to the B, C region, with two components, one fast and one slow; the proton corresponds to D, E two parts. The detector skillfully designs two different luminous scintillators into one detector, eliminates the influence of charged particles and greatly saves space cost. The principle is shown in fig. 3a, 3b and 3c, when neutrons or gamma rays enter the inner layer liquid flash, the neutrons or the gamma rays are distinguished by utilizing the n-gamma discrimination capability (luminescence decay time difference). The charged particles such as proton act in the outer layer scintillator firstly, then enter the inner layer scintillator to act, because of the difference of the luminescence decay time of the scintillator, the signal of the proton forms a higher peak and a longer tail, and when the neutron or gamma ray acts in the outer layer scintillator only, the pulse shape is different from the proton signal, thus the charged particles can be removed by the anti-coincidence method. The neutron, the gamma ray and the charged particle can be effectively distinguished by adopting a special electronic circuit and a pulse shape discrimination method. And (4) obtaining a surrounding neutron energy spectrum by resolving the spectrum of the neutron pulse amplitude spectrum measured by the inner layer liquid scintillation.

However, this detector has a significant disadvantage: the detection medium is all organic material, and is sensitive to high-energy neutrons (neutrons with energy greater than 0.1MeV), and the scintillator on the outer layer only has the functions of anti-coincidence with charged particles. Can not meet the requirements of neutrons with various energies in the space, and can not effectively detect gamma rays.

Therefore, the method expands the measurement energy range and the detection ray types of the conventional spatial neutron detector, and has the characteristics of miniaturization and simple structure, thereby being one of the key directions of spatial neutron detection research.

Disclosure of Invention

The invention provides a detector capable of measuring low-energy neutrons and high-energy neutrons simultaneously, aiming at solving the defect that the conventional neutron detector can only measure high-energy neutrons and being inspired by the principle structure of a sandwich detector. The novel sandwich type neutron detector is provided by utilizing the detection characteristic of the novel CLYC scintillator to low-energy neutrons and good n-gamma discrimination capability. CLYC crystals and organic scintillators with n-gamma discrimination are used as detection media, and different particles are discriminated by using different light-emitting times and a pulse shape discrimination method. The detector overcomes the defect that the existing detector can not measure low-energy neutrons, and can measure the low-energy neutrons and the high-energy neutrons simultaneously. Meanwhile, the device has the capability of removing gamma photons, protons and electrons, and has the advantages of miniaturization, simple structure and the like.

Novel elpasolite crystal CLYC (Cs)₂LiYCl₆) Has better n-gamma resolution capability and is better than the common EJ-301 scintillator. Due to inclusion of⁶Li element can be used for detecting slow neutrons (neutrons with energy lower than 0.1MeV, such as thermal neutrons, low-energy neutrons and the like), response can reach 70000ph/n (3.2MeVee), detection efficiency reaches 85% (thickness of 1cm,⁶CLYC crystals with a Li content of 95%). And due to the inclusion of³⁵Cl has certain response to fast neutrons (neutrons with energy higher than 0.1MeV, such as high-energy neutrons) and good linearity of response, and is expected to be used as a material of a fast neutron spectrum detector. It also has better resolution (4% FWHM @662KeV) and moderate light yield (about 20000 ph/gamma) when it reacts with gamma rays, and is therefore promising as an n-gamma dual-mode detector.

The technical scheme of the invention is to provide a detector capable of simultaneously measuring low-energy neutrons and high-energy neutrons, which is characterized in that: comprises a CLYC crystal, an organic scintillator, a light guide and a photomultiplier;

the CLYC crystal is an elpasolite crystal; the organic scintillator has neutron-gamma pulse shape discrimination capability; the elpasolite crystals and the organic scintillator form a sandwich structure;

the light guide is used for coupling the light emission of incident particles in the organic scintillator and the CLYC crystal;

the photomultiplier is used for detecting the coupled light detection.

Further, the elpasolite-like crystals are Cs₂LiYCl₆、CLLC(Cs₂LiLaCl₆)、CLLB(Cs₂LiLaBr₆) Or CLYB (Cs)₂LiYBr₆)。

Further, the organic scintillator is a liquid scintillator or a plastic scintillator.

Further, the above organic scintillator includes a first organic scintillator;

the sandwich structure comprises:

the CLYC crystal forms a wrapping layer and wraps the outer surface of the first organic scintillator, and the CLYC crystal and the first organic scintillator form a whole.

Further, the thickness of the wrapping layer corresponds to the range of the energy of the proton to be reflected. Such as: 20. the range of 30, 40, 50MeV protons in the CLYC crystal is 3.56, 7.21, 11.93, 17.64mm, respectively, and can be selected accordingly. Since the electrons do not have a fixed range, part of the electrons can be partially blocked by the outer layer crystals.

Further, the organic scintillator includes a first organic scintillator and a second organic scintillator; the second organic scintillator has a light emission decay time faster than that of the CLYC crystal but slower than that of the first organic scintillator;

another sandwich structure may be formed:

the first organic scintillator forms a first wrapping layer which wraps the outside of the CLYC crystal;

the second organic scintillator forms a second wrapping layer wrapping the outer surface of the first organic scintillator, and the second organic scintillator, the first organic scintillator and the second organic scintillator form a whole.

Further, the thickness of the second wrapping layer corresponds to the range of the energy of the proton to be reflected. The range of protons of 20, 30, 40 and 50MeV in the outer layer crystal is 3.8, 7.89, 13.3 and 19.92mm respectively. The size of other scintillators is determined by the type of particles that need to be detected with emphasis in the radiation field environment, such as: if more low-energy neutrons need to be detected, the size of the CLYC crystal is properly increased, and if more fast neutrons need to be detected, the size of the intermediate scintillator is increased.

The invention has the beneficial effects that:

1. the detector has a large energy measurement range;

the existing detector mainly uses an organic scintillator to measure neutrons, and the detection range of the existing detector is fast neutrons with energy larger than 0.1 MeV. The invention is based on CLYC (Cs)₂LiYCl₆:Ce³⁺) The elpasolite crystal and organic scintillator form a sandwich-type neutron detector, because the CLYC crystal contains⁶Li has higher detection efficiency on low-energy neutrons, so the invention can detect neutrons from thermal neutrons (neutrons with energy lower than 0.1MeV) to-100 MeV; the defect that the conventional detector can only measure fast neutrons (more than 0.1MeV) is overcome; the energy measurement range of the existing detector is expanded.

2. The invention can effectively distinguish neutrons and gamma rays;

the novel elpasolite crystal CLYC (Cs2LiYCl6) (or other types of elpasolite crystals) is combined with the fast and slow plastic scintillators to form a whole, so that neutrons and gamma rays can be effectively distinguished, and meanwhile, the influence of high-energy charged particles such as protons and electrons can be eliminated.

3. Besides detecting neutrons, the inorganic scintillator CLYC also has the capability of detecting gamma rays;

since the CLYC crystal is an inorganic crystal, it can be mainly used for detecting gamma rays. The method can be combined with other organic scintillations with neutron-gamma discrimination capability to effectively detect gamma rays.

4. Through reasonable design, the detection efficiency of the detector for neutrons with different energies is close to the neutron fluence-dose conversion factor, and the detector is expected to be designed into a detector with approximate equivalent dose.

5. The structure is simple;

only one detector is needed to enable measurement of neutron gamma and even proton electrons.

Drawings

Fig. 1 is a schematic diagram of an m.takada sandwich detector configuration;

fig. 2 is a detection result of the m.takada sandwich detector in the mixed field test;

fig. 3a is a schematic diagram of the detection of gamma rays by the m.takada sandwich detector;

fig. 3b is a schematic diagram of a m.takada sandwich detector detecting neutrons;

fig. 3c is a schematic diagram of the m.takada sandwich detector detecting protons;

FIG. 4 is a schematic diagram of a detector according to an embodiment of the present invention;

the reference numbers in the figures are: 1-CLYC crystal, 2-organic scintillator (with neutron-gamma discrimination), 3-light guide, 4-photomultiplier tube, 5-light guide shell (shading material);

FIG. 5 is a schematic diagram of a second embodiment of the present invention;

the reference numbers in the figures are: 5-CLYC crystal, 6-first organic scintillator (with neutron-gamma discrimination), 7-second organic scintillator (with slower luminescence time than the first type of scintillator, e.g., EJ-240), 8-light guide, 9-photomultiplier;

FIG. 6 is a representative measured waveform for several types of scintillators in an embodiment of the invention;

Detailed Description

The principles and features of this invention are described in conjunction with the accompanying drawings and the embodiments, which are set forth merely for purposes of illustration and are not intended to limit the scope of the invention.

The sandwich type detector structure provided by the invention is based on different scintillator luminescence decay time, so that the scintillator luminescence decay time and the scintillator luminescence decay time form a detector, and the judgment of different particles is realized by a particle waveform discrimination method. Fig. 6 is a typical measured waveform for several types of scintillators used in the present invention, where the waveform for the CLYC crystal is wider, the EJ-299-33A scintillator emits light more narrowly, and the EJ-240 scintillator has a waveform in between the first two. The scintillator type in the figure is only selected from its representative type, and does not limit the scintillator type of the present invention and must be employed.

Example one

As shown in fig. 4, the detector of the present embodiment includes a CLYC crystal 1, an organic scintillator 2, a light guide 3, and a photomultiplier tube 4. The CLYC crystal 1 is potassium cryolite crystal Cs₂LiYCl₆Other types of elpasolite-like crystals are also possible, including: CLLC (Cs)₂LiLaCl₆)、CLLB(Cs₂LiLaBr₆)、CLYB(Cs₂LiYBr₆) And the like. The organic scintillator 2 is an organic scintillator with neutron-gamma pulse shape discrimination capability, and comprises a liquid scintillator EJ-301 (or BC501A) and the like, and can also be a similar plastic scintillator, such as EJ-299-33A, stilbene crystal and the like.

The external surface of the organic scintillator 2 is wrapped with the CLYC crystal 1, the two are integrated, and the light emitted by the incident particles in the organic scintillator 2 or the CLYC crystal 1 is coupled by the light guide 3 and then enters the photomultiplier tube 4 for detection.

The CLYC crystal 1 functions to detect neutrons, especially low-energy neutrons below 0.1MeV, in addition to anticounterfeiting charged particles (i.e., charged particles with too low an energy cannot enter the organic scintillator 2). Due to neutrons and in CLYC⁶The Li effect produces α and T, which can be distinguished from the charged particles p, e around the detector by pulse shapingAnd (5) realizing shape discrimination. The neutron energy spectrum is realized by the spectrum resolution of the organic scintillator 2 with n-gamma discrimination capability in the inner layer.

Refer to events (r) -events (c) in fig. 4, and CLYC crystal, EJ-299-33A, and waveforms in fig. 6. The event (i) is that protons only act in the CLYC crystal 1, and the event (iii) is that electrons only act in the CLYC crystal 1, the two events cannot enter the organic scintillator 2, and the luminescence in the CLYC crystal 1 alone can be distinguished by waveform discrimination after being recorded by a photomultiplier. The higher energy proton event (r) and electron event (c) may also penetrate the CLYC crystal 1, becoming a superposition of event (r) and event (r) for proton events, and event (r) for electron events. For the two processes, because the two scintillators have slow response to protons and fast response to electrons, the scintillators can be distinguished by waveform discrimination. For neutron events, due to strong penetrability, the neutron events can only act in the outer-layer CLYC crystal 1 (event [ ]), can also only act in the inner-layer organic scintillator 2 (event [ ]), and can also be superposition of event [ ], and event [ ]. Especially, the action of neutrons in the organic scintillator 2 has a waveform similar to that of protons, and cannot be distinguished, but the difference is that protons need to act with the organic scintillator 2 in the inner layer and must first act with the CLYC crystal 1 in the outer layer, so that different waveform discrimination signals are formed. In addition, if the neutron event occurs, only the proton event occurs, that is, both the neutron and the proton only act on the CLYC crystal 1, and if the neutron event occurs in the (n, α) reaction and the proton only in the p reaction, the situation can be distinguished from the waveform discrimination. If the neutron is generated by (n, p) reaction, the waveform is distinguished according to the energy of the proton, and the proton with different energy is also distinguished according to the difference of the waveforms acted in the CLYC crystal. However, if the (n, p) reaction of the neutron occurs, the energy of the incident neutron is equivalent, the event is difficult to distinguish, but the probability of the event occurrence is small and can be ignored. For an energy less than 0.1MeV, which can emit light only in the external CLYC crystal 1, even if it enters the internal organic scintillator 2, its light emission signal is weak and light output effectively detected by the photomultiplier tube cannot be performed. Thus, this feature can be exploited to detect lower energy neutrons.

Example two

As shown in fig. 5, the detector of the present embodiment includes a CLYC crystal 5, a first organic scintillator 6, a second organic scintillator 7, a light guide 8, and a photomultiplier tube 9. The CLYC crystal 5 is the same type of CLYC crystal material as in example one. The first organic scintillator 6 is the same in material type as the organic scintillator 2 in embodiment one. The second organic scintillator 7 is a plastic scintillator, such as EJ-240, which has a faster luminescence decay time than the CLYC crystal but a slower luminescence decay time than the first organic scintillator 6. The light emission waveforms of the three scintillators are shown in figure 6.

A first organic scintillator 6 is surrounded on the outer layer of the CLYC crystal 5, and a second organic scintillator 7 is surrounded on the outer layer of the first organic scintillator 6. The three components form a whole, and the light emitted by the incident particles in the second organic scintillator 7, the first organic scintillator 6 or the CLYC crystal 5 is coupled by the light guide 8 and then enters the photomultiplier 9 for detection.

The second organic scintillator 7 on the outer layer emits light slowly and is used for reflecting charged particles; the middle first organic scintillator 6 has fast luminescence and neutron n-gamma discrimination capability and is used for solving a fast neutron energy spectrum; the CLYC scintillator 5 is arranged at the innermost layer and is mainly used for detecting thermal neutrons or gamma rays. The structure has the advantages that the outer layer organic scintillator can be used as a luminescent material and also can be used as a moderating material of the inner layer CLYC scintillator, and the low-energy neutron detection efficiency is improved.

Referring to fig. 5, event a is the action of protons only in the second organic scintillator 7, event b is the action of protons on the second organic scintillator 7 and then on the first organic scintillator 6, and event c is the action on the CLYC crystal 5 based on the action of the first two scintillators. The events d, e, f of electrons correspond to proton events a, b, c. For event a or d, protons or electrons only act in the second organic scintillator 7, and this event cannot be distinguished because the second organic scintillator 7 does not have neutron-gamma resolving power. But due to the large difference in range between electrons and protons, the probability of such an event is low and negligible. Two other events, the first organic scintillator 6 or the second organic scintillator 7, which have different neutron-gamma waveforms, are passed by protons and electrons, and can be distinguished by waveform discrimination. For neutrons, since the first organic scintillator in the middle part has a large volume, most of the neutrons should react with the first organic scintillator 6 (event g), and a neutron energy spectrum can be obtained by a method of spectrum decomposition. The waveform of event j, where neutrons directly interact with the CLYC crystal 5, is different from the waveform of protons, which generate different signals because they interact with the scintillator of the outer layer to reach the CLYC crystal 5. Neutron events g + h and g + i, wherein the waveforms of the two events are the same in the ClYC crystal 5, but the h event is a fast organic scintillator event, the i event is a slow scintillator event, and the waveforms are different after the two events are mutually superposed.

In the two examples, the neutron is measured by the accelerator, and the detection efficiency of the detector for neutrons with different energies can be obtained by distinguishing different events, so that the fluence of the neutrons can be back-inferred through the measured spectrum. The fast neutron part (with energy greater than 0.1MeV) is unscrambled mainly for the event of the effect of the organic scintillator 2 in fig. 4, and a relatively accurate neutron spectrum can be obtained. For low-energy neutrons, use is made of⁶And (3) under the action of Li, generating alpha particles or tritium particles, and realizing the measurement of low-energy neutrons. By adjusting the size of each part of the scintillator, the anti-coincidence measurement of protons and electrons with different energies and the measurement of neutron fluence or energy spectrum are realized.

Furthermore, since both structures contain CLYC crystal and organic crystal, the probability of the gamma ray acting on the organic crystal is low, and the probability of the gamma ray acting on the inorganic crystal is high, and meanwhile, because the gamma ray acting on the scintillator mainly emits Compton electrons, the gamma ray can be distinguished by the neutron-gamma resolution capability of the scintillator. For events that cannot be distinguished, such as: events that electrons directly act on the CLYC scintillator and events that gamma acts on the CLYC scintillator only have small probability and can be ignored. In the detection of gamma rays, a gamma energy spectrum can also be obtained by a spectrum solution method.

Claims

1. A detector capable of simultaneously measuring low-energy neutrons and high-energy neutrons is characterized in that: comprises a CLYC crystal, an organic scintillator, a light guide and a photomultiplier;

the photomultiplier is used for detecting the coupling light;

the organic scintillator comprises a first organic scintillator and a second organic scintillator; the second organic scintillator has a luminescence decay time faster than the CLYC crystal but slower than the first organic scintillator;

the sandwich structure is as follows:

the first organic scintillator forms a first wrapping layer and wraps the outer surface of the CLYC crystal;

2. The detector of claim 1, wherein the detector is capable of simultaneously measuring low-energy and high-energy neutrons, and further comprising: the elpasolite-like crystals are Cs₂LiYCl₆、Cs₂LiLaCl₆、Cs₂LiLaBr₆Or Cs₂LiYBr₆。

3. The detector of claim 1, wherein the detector is capable of simultaneously measuring low-energy and high-energy neutrons, and further comprising: the organic scintillator is a liquid scintillator or a plastic scintillator.

4. The detector of claim 1, wherein the detector is capable of simultaneously measuring low-energy and high-energy neutrons, and further comprising: the thickness of the second wrapping layer corresponds to the range of the energy of the proton which needs to be reflected.