CN109143316B - Neutron detection method and equipment for reducing gamma-ray interference by utilizing NaI (TI) scintillator - Google Patents
Neutron detection method and equipment for reducing gamma-ray interference by utilizing NaI (TI) scintillator Download PDFInfo
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- CN109143316B CN109143316B CN201710455265.4A CN201710455265A CN109143316B CN 109143316 B CN109143316 B CN 109143316B CN 201710455265 A CN201710455265 A CN 201710455265A CN 109143316 B CN109143316 B CN 109143316B
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- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T3/00—Measuring neutron radiation
- G01T3/06—Measuring neutron radiation with scintillation detectors
Abstract
The invention belongs to the technical field of radiometry, in particular to a neutron detection method and equipment for reducing gamma-ray interference by utilizing a NaI (TI) scintillator, which uses 6 When LiI scintillator detector detects neutrons in mixed radiation field, the LiI scintillator detector and the mixed radiation field are combined 6 A first voltage amplitude discrimination threshold is set in a first comparison circuit connected with the LiI scintillator, and the first voltage amplitude discrimination threshold is set 6 The method for detecting neutrons comprises the following steps of: (S1) at 6 A NaI (TI) scintillator detector which adopts a NaI (TI) scintillator is arranged near the LiI scintillator; (S2) setting a second voltage amplitude discrimination threshold in a second comparison circuit connected with the NaI (TI) scintillator; (S3) record employed 6 A first signal measured by the LiI scintillator; recording a second signal measured using a NaI (TI) scintillator; (S4) multiplying the second signal by a correction factor, and subtracting the second signal multiplied by the correction factor from the first signal to obtain a net neutron count rate.
Description
Technical Field
The invention belongs to the technical field of radiation measurement, and particularly relates to a neutron detection method and equipment for reducing gamma-ray interference by utilizing a NaI (TI) scintillator.
Background
It is well known that the space particle radiation environment includes not only charged particles such as protons and electrons, but also uncharged particles such as neutrons (n) and X-rays. Neutrons have been a major uncharged particle, and neutron-related detection techniques have been a focus of research. Because a large amount of gamma rays are often accompanied in the presence of neutrons, the removal of interference of gamma rays on neutron signals is a research hotspot and difficulty in the field of neutron detection. The screening of neutrons and gamma rays is the basis of neutron detection technologies such as contraband detection, environmental radiation detection, military and deep space detection, and has extremely important theoretical and practical significance.
The neutron detector is selected with the exception of various performance metrics and parameters such as efficiency of neutron detection, energy or time-resolved performance, lifetime, etc. There is also a concern about whether it has good gamma-ray discrimination or poor gamma-ray response. 6 LiI scintillators are an important detector in neutron detection technology (is a high efficiency detector for detecting slow neutrons, especially thermal neutrons; e.g. 10mm thickness, enrichment) 6 The detection efficiency of the Li lithium iodide scintillator for thermal neutrons reaches 100 percent, the material density is high, the stopping power is strong, the detection sensitivity is high, and the material is sensitive to gamma rays (see figure 2). The experiment shows that the preparation method has the advantages of, 6 the LiI scintillator has better gamma radiation resistance under the irradiation of low-energy gamma rays. But for high energy gamma rays with energies greater than 1MeV, the detection sensitivity is high, which is extremely detrimental to its mid-detection. Thus using 6 How to reduce or eliminate the gamma-ray response of LiI scintillators when detecting neutron rays is one of the key issues that they have to solve. At present, using 6 When the LiI scintillator is used as a detector of the neutron dose equivalent rate instrument, the gamma ray signals are removed mainly by adopting a pulse amplitude discrimination technology, namely, neutron rays and gamma rays are utilized in the process of 6 Generation in LiI scintillatorsThe difference of the signal pulse amplitude is that 6 And a voltage amplitude discrimination threshold is set in a comparison circuit connected with the LiI scintillator, and gamma pulses with lower amplitude are blocked, so that only neutron signals are recorded. This method works well with lower gamma energy, but ignores the high energy gamma rays at 6.0MeV 6 The energy deposited in the LiI scintillator can be summed 6 Li (α, n) reacts as much. The actual n-gamma ratio drops from 1000:1 at 1.0MeV to 1:1 at 6.0 MeV. The gamma-ray induced response will severely interfere with the neutron dose measurement, so that the usual pulse amplitude discrimination technique will produce a large deviation in the case of a mixed radiation field with high energy gamma rays.
Disclosure of Invention
For effective use 6 The LiI scintillator detects neutron rays, and gamma ray interference is extremely necessary to be reduced through a gamma ray signal discrimination technology. Considering that NaI (TI) scintillators have the advantage of being sensitive to gamma particle radiation and relatively insensitive to neutron radiation, this characteristic is very significant in improving the effective shielding of gamma radiation interference when measuring neutron rays in an n, gamma mixed radiation field, and therefore, will 6 The two scintillators, liI and NaI (TI), combine to detect neutron radiation. In detecting a mixed radiation field, from 6 And the output signal of the NaI (TI) scintillator is buckled according to the corresponding proportion in the output signal of the LiI scintillator, so that the net neutron signal in the mixed radiation field can be obtained.
In order to achieve the aim, the invention adopts the technical proposal that the NaI (TI) scintillator is utilized to reduce the neutron detection method of gamma-ray interference, and the invention adopts 6 LiI scintillator 6 When the LiI scintillator detector detects neutron rays in the mixed radiation field, the LiI scintillator detector and the neutron rays in the mixed radiation field are detected 6 Setting a first voltage amplitude discrimination threshold in a first comparison circuit connected with the LiI scintillator, and carrying out the steps 6 The method for detecting neutrons by utilizing the NaI (TI) scintillator to reduce gamma ray interference comprises the following steps of:
(S1) in the process 6 A NaI (TI) scintillator detector which adopts a NaI (TI) scintillator is arranged near the LiI scintillator;
(S2) setting a second voltage amplitude discrimination threshold in a comparison circuit connected with the NaI (TI) scintillator, and filtering out the signals of the low-energy gamma rays detected by the NaI (TI) scintillator;
(S3) recording the first signal and the second signal; the first signal includes the 6 Counting rates of the neutron rays and the high-energy gamma rays measured by the LiI scintillator; the second signal is the count rate of the high-energy gamma rays measured by the NaI (TI) scintillator;
(S4) calculating a net neutron count rate, multiplying the second signal by a correction coefficient, and obtaining the net neutron count rate by subtracting the second signal multiplied by the correction coefficient from the first signal.
Further, the first voltage amplitude discrimination threshold is that the gamma ray energy is 662keV 6 The voltage amplitude value obtained by detection of the LiI scintillator;
the second voltage amplitude discrimination threshold is the voltage amplitude detected by the NaI (TI) scintillator when the energy of the gamma rays is 662 keV;
the low-energy gamma rays refer to gamma rays with energy less than or equal to 662 keV; the high-energy gamma rays refer to gamma rays with energy greater than 662 keV.
Further, in said step (S1), also included in said 6 A neutron response layer is arranged outside the LiI scintillator; the NaI (TI) scintillator is arranged in the middle of the neutron response layer; the neutron response layer is a polyethylene moderating body; the thickness of the polyethylene moderated body is 8-10cm.
Further, the method comprises the steps of,
the obtaining of the correction coefficient in the step (S4) includes the steps of:
(S4.1) a gamma radiation source having an energy of 662keV-3MeV is disposed at a distance from the 6 The LiI scintillator and the NaI (TI) scintillator are arranged on an irradiation position with a linear distance of 60 cm;
(S4.2) generating a different energy between 662keV-3MeV using said gamma radiation sourceGamma-ray irradiation of the measuring section 6 LiI scintillator, naI (TI) scintillator, and recording the same 6 The counting rates of the LiI scintillator and the NaI (TI) scintillator measured under the gamma ray irradiation of different energy sections;
(S4.3) calculating the gamma-ray irradiation of the same energy segment 6 Ratios of count rates measured for LiI scintillators, naI (TI) scintillators;
(S4.4) averaging the ratio measured under gamma irradiation of each of the energy segments in step (S4.3), the average being the correction factor.
Further, the calculation formula of the net neutron counting rate is as follows:
H (n) ＝H (n,γ) -H (γ) *K
wherein:
H (n) -the net neutron count rate resulting;
H (n,γ) -from said 6 Neutron rays measured by LiI scintillators and methods of use thereof 6 A count rate of the high energy gamma rays having an energy measured by the LiI scintillator higher than 662 keV;
H (γ) -the count rate of the high energy gamma rays measured by the NaI (TI) scintillator is higher than 662 keV;
k—correction coefficient for subtracting the count rate of the high energy gamma rays measured by the NaI (TI) scintillator with energies above 662 keV.
To achieve the above object, the present invention also discloses a neutron detection apparatus for reducing gamma-ray interference using NaI (TI) scintillator for the neutron detection method described above, comprising 6 LiI scintillator detector, the 6 The LiI scintillator detector comprises the following components which are connected in sequence 6 LiI scintillator, PIN emitting diode with bias voltage, first pre-amplifier circuit, first comparison circuit, first shaping circuit, SCM system, wherein a first voltage amplitude discrimination threshold is set in the first comparison circuit to make the first voltage amplitude discrimination threshold 6 Filtering out signals of low-energy gamma rays detected by the LiI scintillator; wherein, it also comprisesAnd a NaI (TI) scintillator detector which is connected with the singlechip system and adopts a NaI (TI) scintillator is included, a second voltage amplitude discrimination threshold value is set in a comparison circuit which is connected with the NaI (TI) scintillator, and signals of low-energy gamma rays which are measured by the NaI (TI) scintillator are filtered.
Further, the NaI (TI) scintillator detector comprises an NaI (TI) scintillator, a photomultiplier provided with high voltage, a second pre-amplifying circuit, a second comparing circuit and a second shaping circuit which are sequentially connected, wherein the second shaping circuit is connected with the singlechip system;
the second voltage amplitude discrimination threshold is set in the second comparison circuit.
Further, the first voltage amplitude discrimination threshold is that the gamma ray energy is 662keV 6 The voltage amplitude value obtained by detection of the LiI scintillator;
the second voltage amplitude discrimination threshold is the voltage amplitude detected by the NaI (TI) scintillator when the energy of the gamma rays is 662 keV;
the low-energy gamma rays refer to gamma rays with energy less than or equal to 662 keV; the high-energy gamma rays refer to gamma rays with energy greater than 662 keV.
Still further, in the described 6 A neutron response layer is arranged outside the LiI scintillator, and the NaI (TI) scintillator is arranged close to the LiI scintillator 6 The position of the LiI scintillator; the neutron response layer is used for slowing down the neutron rays to be detected into thermal neutrons, so that the neutron rays are convenient to use 6 And measuring the neutron rays by the LiI scintillator.
Further, the NaI (TI) scintillator is disposed at the 6 The neutron response layer outside the LiI scintillator is in the middle.
Further, the neutron response layer is a polyethylene moderated body, and the thickness of the polyethylene moderated body is 8-10cm.
The invention has the beneficial effects that:
the monitoring of the mixed radiation field of neutrons with gamma rays is facilitated, and more favorable conditions are provided for radiation protection work, wherein:
1. by and at 6 A first voltage amplitude discrimination threshold is set in a first comparison circuit connected with the LiI scintillator, so that interference of low-energy gamma rays on neutron measurement is solved; by at least one of 6 A NaI (TI) scintillator detector adopting a NaI (TI) scintillator is arranged near the LiI scintillator, and a second voltage amplitude discrimination threshold is arranged in a comparison circuit connected with the NaI (TI) scintillator, so that interference of high-energy gamma rays on neutron measurement is solved;
2. by definitely defining the first voltage amplitude discrimination threshold and the second voltage amplitude discrimination threshold, the method ensures 6 The LiI scintillator and the NaI (TI) scintillator filter the signals of the low-energy gamma rays, so that the accuracy of the final net neutron counting rate is ensured; accurately distinguish low-energy gamma rays and high-energy gamma rays by taking 662keV energy as boundary, ensure 6 The LiI scintillator filters the signals of the low-energy gamma rays, so that the accuracy of the NaI (TI) scintillator for measuring the high-energy gamma rays is ensured;
3. by at least one of 6 The neutron response layer arranged outside the LiI scintillator can increase the response of neutrons (neutron rays) and improve 6 The detection effect of the LiI scintillator on neutrons (neutron rays); the NaI (TI) scintillator is arranged in the middle of the neutron response layer, so that the detection effect of the NaI (TI) scintillator on the high-energy gamma rays can be ensured to be more accurate;
4. the material and thickness of the mesoresponsive layer are optimized (the material is polyethylene moderated body, the thickness is 8-10 cm) 6 The LiI scintillator has more accurate detection effect on neutrons (neutron rays);
5. the accuracy of calculating the net neutron count rate can be further improved by optimizing the numerical range of the correction coefficient.
Drawings
FIG. 1 is a schematic diagram of a peripheral circuit configuration of a neutron detection device utilizing NaI (TI) scintillators to reduce gamma-ray interference, according to an embodiment of the present invention;
FIG. 2 is a schematic illustration of the prior art 6 A response curve graph of the LiI scintillator to thermal neutrons (neutron rays after moderation by the neutron response layer) and gamma rays;
FIG. 3 is a graph of the energy response of a NaI (TI) scintillator to gamma rays in accordance with an embodiment of the present invention; wherein the abscissa represents the energy of the gamma rays and the ordinate represents the response of the NaI (TI) scintillator to the gamma rays;
in the figure: 1- 6 LiI scintillator, 2-PIN light emitting diode, 3-bias voltage, 4-first pre-amplifier circuit, 5-first comparator circuit, 6-first shaping circuit, 7-singlechip system, 8-NaI (TI) scintillator, 9-photomultiplier, 10-second pre-amplifier circuit, 11-second comparator circuit, 12-second shaping circuit, 13-high voltage.
Detailed Description
The invention is further described below with reference to the drawings and examples.
The NaI (TI) scintillator has the characteristics of strong blocking capability to charged particles, higher luminous efficiency, good energy linearity, high sensitivity and high detection efficiency to gamma rays, the energy response of the NaI (TI) scintillator is not linear, the NaI (TI) scintillator needs to be subjected to corresponding energy compensation in order to obtain better energy response, the energy response of the NaI (TI) scintillator after the energy compensation is good, and the response of gamma rays in the energy range from more than 100 keV to 3MeV tends to be stable (see the energy response curve of the NaI (TI) scintillator to the gamma rays in FIG. 3). Meanwhile, naI (TI) scintillators are insensitive to neutron ray response, and 6 the response of the LiI scintillator to the sub-rays is negligible compared, and therefore, in 6 A NaI (TI) scintillator detector is arranged near the LiI scintillator 6 The count rate measured by the LiI scintillator is subtracted from the count rate measured by the NaI (TI) scintillator in a corresponding proportion to obtain a more accurate net neutron count rate.
The neutron detection method for reducing gamma-ray interference by utilizing the NaI (TI) scintillator provided by the invention adopts 6 LiI scintillator 6 When the LiI scintillator detector detects neutron rays in the mixed radiation field, the LiI scintillator detector is used for solving the influence of low-energy gamma rays on the measurement effect 6 A first voltage amplitude discrimination threshold is set in a first comparison circuit connected with the LiI scintillator, and the first voltage amplitude discrimination threshold is set 6 Signal filtering of low-energy gamma rays measured by LiI scintillatorDropping; thereby recording only the signal of the detected neutron ray; in order to solve the influence of high-energy gamma rays on the measurement effect, the method comprises the following steps:
step S1, in 6 A NaI (TI) scintillator detector which adopts a NaI (TI) scintillator is arranged near the LiI scintillator;
step S2, setting a second voltage amplitude discrimination threshold in a comparison circuit connected with the NaI (TI) scintillator, and filtering out signals of low-energy gamma rays detected by the NaI (TI) scintillator;
step S3, recording adoption 6 A first signal measured by the LiI scintillator, the first signal including 6 Counting rates of neutron rays and high-energy gamma rays measured by the LiI scintillator; recording a second signal measured by using a NaI (TI) scintillator, wherein the second signal is the counting rate of the high-energy gamma rays measured by the NaI (TI) scintillator;
and S4, calculating a net neutron count rate, multiplying the second signal by a correction coefficient, and subtracting the second signal multiplied by the correction coefficient from the first signal to obtain the net neutron count rate.
The obtaining of the correction coefficient in step S4 includes the steps of:
step S4.1, the gamma radiation source with the energy of 662keV-3MeV is arranged at a distance 6 The LiI scintillator and the NaI (TI) scintillator are arranged on an irradiation position with a linear distance of 60 cm;
step S4.2, generating gamma-ray irradiation of different energy segments between 662keV-3MeV by gamma-ray source 6 LiI scintillator, naI (TI) scintillator, and recording 6 The counting rates of the LiI scintillator and the NaI (TI) scintillator measured under the gamma ray irradiation of different energy sections;
step S4.3, calculating the gamma-ray irradiation under the same energy section 6 Ratios of count rates measured for LiI scintillators, naI (TI) scintillators;
and step S4.4, averaging the ratio measured under the gamma-ray irradiation of each energy segment in the step S4.3, wherein the average value is the correction coefficient.
The specific values of the correction factors will vary depending on the type, size, etc. of NaI (TI) scintillator selected.
In order to enhance the response of neutrons (neutron rays), the method is also included in step (S1) 6 LiI scintillator detector 6 A neutron response layer is arranged outside the LiI scintillator; disposing a NaI (TI) scintillator in a middle portion of the neutron response layer; the neutron response layer is a polyethylene moderating body; the thickness of the polyethylene moderated body is 8-10cm
Wherein when the first voltage amplitude discrimination threshold is 662keV of gamma rays energy 6 The voltage amplitude value obtained by detection of the LiI scintillator;
the voltage amplitude detected by the NaI (TI) scintillator when the second voltage amplitude discrimination threshold is 662keV of gamma rays;
the low-energy gamma rays refer to gamma rays with energy less than or equal to 662 keV; high energy gamma rays refer to gamma rays having energies greater than 662 keV. In the present invention, the high energy gamma rays are specifically gamma rays between 662keV and 3 MeV.
The calculation formula of the net neutron count rate is as follows:
H (n) ＝H (n,γ) -H (γ) *K
wherein:
H (n) -the net neutron count rate resulting;
H (n,γ) -by 6 The counting rate of neutron rays and high-energy gamma rays with energy higher than 662keV measured by the LiI scintillator;
H (γ) -a count rate of high energy gamma rays with an energy higher than 662keV measured by a NaI (TI) scintillator;
k-correction factor for subtracting the count rate of high energy gamma rays measured by NaI (TI) scintillators above 662 keV.
Thus, the method provided by the invention can give the net neutron count rate of the mixed radiation field for the mixed radiation field with unknown energy and unknown fluence, no matter whether the gamma rays belong to high energy or low energy.
The above-mentioned conditions for discriminating the two scintillator detectors when the gamma ray is 662keV are considered because:
1. at a gamma-ray energy of 662keV, 6 LiI scintillator abilityThe measured amplitude is obviously smaller than the amplitude obtained by detecting thermal neutrons (neutron rays after being slowed down by a neutron response layer);
2. gamma-ray energies on the order of 662keV to 3MeV, with NaI (TI) scintillators responding more stably in this energy range;
the Cs-137 radioactive source emits gamma rays with energy of 662keV, which is easily obtained as an experimental condition.
The invention also discloses neutron detection equipment for reducing gamma-ray interference by utilizing the NaI (TI) scintillator, and the neutron detection equipment is used for measuring the net neutron counting rate in the mixed radiation field by using the neutron detection method. The neutron detection device comprises 6 LiI scintillator detectors and NaI (TI) scintillator detectors (see fig. 1).
Wherein, the liquid crystal display device comprises a liquid crystal display device, 6 the LiI scintillator detector comprises sequentially connected 6 The LiI scintillator 1, the PIN light emitting diode 2 (provided with the bias voltage 3), the first pre-amplifying circuit 4, the first comparing circuit 5, the first shaping circuit 6 and the singlechip system 7, wherein a first voltage amplitude discrimination threshold value is set in the first comparing circuit 5 to be 6 The signals of the low-energy gamma rays detected by the LiI scintillator 1 are filtered;
the NaI (TI) scintillator detector is also connected with the singlechip system 7 and is used for recording signals of high-energy gamma rays. The NaI (TI) scintillator detector comprises a NaI (TI) scintillator 8, a photomultiplier 9 (provided with a high voltage 13), a second pre-amplifying circuit 10, a second comparing circuit 11 and a second shaping circuit 12 which are connected in sequence; wherein the second shaping circuit 12 is connected with the singlechip system 7. A second voltage amplitude discrimination threshold is set in the second comparison circuit 11, and the low-energy gamma ray signal detected by the NaI (TI) scintillator 8 is filtered out.
When the first voltage amplitude discrimination threshold is 662keV of gamma rays 6 The voltage amplitude detected by the LiI scintillator 1;
the voltage amplitude detected by the NaI (TI) scintillator 8 when the second voltage amplitude discrimination threshold is 662keV of gamma rays;
the low-energy gamma rays refer to gamma rays with energy less than or equal to 662 keV; high energy gamma rays refer to gamma rays having energies greater than 662 keV. In the present invention, the high energy gamma rays are specifically gamma rays between 662keV and 3 MeV.
At the position of 6 The LiI scintillator 1 is provided with a neutron response layer (to increase neutron response) outside, and the NaI (TI) scintillator 8 is provided close to 6 The LiI scintillator 1 is positioned, and specifically, the NaI (TI) scintillator 8 may be disposed 6 The neutron response layer outside the LiI scintillator 1 is in the middle. The specific position of the (NaI (TI) scintillator 8 can then be determined according to 6 The direction and position of the LiI scintillator 1 are adjusted as much as possible 6 The LiI scintillator 1 is positioned close). The neutron response layer is a polyethylene moderated body. The thickness of the polyethylene moderated body is 8-10cm. The neutron response layer is used for slowing down the neutron rays to be measured into thermal neutrons, and is convenient for 6 Measurement of neutron rays by LiI scintillators.
As shown in figure 1 of the drawings, 6 the LiI scintillator 1 is connected with the PIN light-emitting diode 2, the NaI (TI) scintillator 8 is connected with the photomultiplier 9, signals output by the PIN light-emitting diode 2 and the photomultiplier 9 enter respective pre-amplifying circuits to amplify the signals, and the amplified signals enter respective comparison circuits to perform threshold value screening to obtain a first signal [ ] 6 The count rate of neutrons and high-energy gamma rays detected by the LiI scintillator 1) and a second signal (the count rate of high-energy gamma rays detected by the NaI (TI) scintillator 8). Here the number of the elements is the number, 6 when the threshold value of the discrimination signal (first voltage amplitude discrimination threshold value) of the LiI scintillator 1 is 662keV 6 The magnitude of the voltage detected by the LiI scintillator 1, and the threshold value of the discrimination signal (second voltage magnitude discrimination threshold value) of the NaI (TI) scintillator 8 is also set to the magnitude of the voltage detected by the NaI (TI) scintillator 8 when the gamma ray is 662 keV. This ensures that when the gamma energy is low, 6 the amplitude discrimination technique of the LiI scintillator 1 itself (using the first voltage amplitude discrimination threshold) rejects the portion of low energy gamma rays, whereas at high gamma ray energies, the NaI (TI) scintillator 8 makes a gamma ray energy measurement in the range from 662keV to 3MeV, 6 the first signal measured by the LiI scintillator 1 strips the second signal measured by the NaI (TI) scintillator 8. The first signal and the second signal after passing through the respective comparison circuit enter after passing through the respective shaping circuitThe singlechip system 7 performs data processing to obtain the net neutron count rate.
The calculation formula of the net neutron count rate is as follows:
H (n) ＝H (n,γ) -H (γ) *K
wherein:
H (n) -the net neutron count rate resulting;
H (n,γ) -by 6 The counting rate of neutron rays and high-energy gamma rays with energy higher than 662keV measured by the LiI scintillator 1;
H (γ) -the count rate of high energy gamma rays with energy higher than 662keV measured by the NaI (TI) scintillator 8;
k—correction coefficient for subtracting the count rate of high energy gamma rays measured by NaI (TI) scintillator 8 with energies above 662 keV.
The device according to the invention is not limited to the examples described in the specific embodiments, and a person skilled in the art obtains other embodiments according to the technical solution of the invention, which also belong to the technical innovation scope of the invention.
Claims (8)
1. Neutron detection method for reducing gamma-ray interference by using NaI (TI) scintillator by employing 6 LiI scintillator 6 When the LiI scintillator detector detects neutron rays in the mixed radiation field, the LiI scintillator detector and the neutron rays in the mixed radiation field are detected 6 Setting a first voltage amplitude discrimination threshold in a first comparison circuit connected with the LiI scintillator, and carrying out the steps 6 The method is characterized in that in order to solve the influence of high-energy gamma rays on the measurement effect, the neutron detection method for reducing gamma ray interference by utilizing a NaI (TI) scintillator is adopted, and comprises the following steps:
(S1) in the process 6 A NaI (TI) scintillator detector which adopts a NaI (TI) scintillator is arranged near the LiI scintillator;
(S2) setting a second voltage amplitude discrimination threshold in a comparison circuit connected with the NaI (TI) scintillator, and filtering out the signals of the low-energy gamma rays detected by the NaI (TI) scintillator;
(S3) recording the first signal and the second signal; the first signal includes the 6 Counting rates of the neutron rays and the high-energy gamma rays measured by the LiI scintillator; the second signal is the count rate of the high-energy gamma rays measured by the NaI (TI) scintillator;
(S4) calculating a net neutron count rate, multiplying the second signal by a correction coefficient, and obtaining the net neutron count rate by subtracting the second signal multiplied by the correction coefficient from the first signal;
the first voltage amplitude discrimination threshold is that the energy of the gamma rays is 662keV 6 The voltage amplitude value obtained by detection of the LiI scintillator;
the second voltage amplitude discrimination threshold is the voltage amplitude detected by the NaI (TI) scintillator when the energy of the gamma rays is 662 keV;
the low-energy gamma rays refer to gamma rays with energy less than or equal to 662 keV; the high-energy gamma rays refer to gamma rays with energy larger than 662 keV;
the obtaining of the correction coefficient in the step (S4) includes the steps of:
(S4.1) a gamma radiation source having an energy of 662keV-3MeV is disposed at a distance from the 6 The LiI scintillator and the NaI (TI) scintillator are arranged on an irradiation position with a linear distance of 60 cm;
(S4.2) irradiating the gamma rays of different energy segments between 662keV and 3MeV with the gamma radiation source 6 LiI scintillator, naI (TI) scintillator, and recording the same 6 The counting rates of the LiI scintillator and the NaI (TI) scintillator measured under the gamma ray irradiation of different energy sections;
(S4.3) calculating the gamma-ray irradiation of the same energy segment 6 Ratios of count rates measured for LiI scintillators, naI (TI) scintillators;
(S4.4) averaging the ratio measured under gamma irradiation of each of the energy segments in step (S4.3), the average being the correction factor.
2. Such as weightThe neutron detection method of claim 1, wherein: also included in the step (S1) 6 A neutron response layer is arranged outside the LiI scintillator; the NaI (TI) scintillator is arranged in the middle of the neutron response layer; the neutron response layer is a polyethylene moderating body; the thickness of the polyethylene moderated body is 8-10cm.
3. Neutron detection apparatus for reducing gamma-ray interference using NaI (TI) scintillators for implementing the neutron detection method of any one of claims 1-2, comprising 6 LiI scintillator detector, the 6 The LiI scintillator detector comprises the following components which are connected in sequence 6 LiI scintillator (1), PIN emitting diode (2) that is equipped with offset voltage (3), first pre-amplifier circuit (4), first comparison circuit (5), first shaping circuit (6), singlechip system (7), wherein set up first voltage amplitude and discriminate threshold value in first comparison circuit (5), will the said 6 Filtering out signals of low-energy gamma rays detected by the LiI scintillator; the method is characterized in that: the system also comprises a NaI (TI) scintillator detector which is connected with the singlechip system (7) and adopts a NaI (TI) scintillator (8), wherein a second voltage amplitude discrimination threshold value is set in a comparison circuit which is connected with the NaI (TI) scintillator (8), and signals of low-energy gamma rays which are measured by the NaI (TI) scintillator (8) are filtered.
4. A neutron detection device according to claim 3, wherein:
the NaI (TI) scintillator detector comprises an NaI (TI) scintillator (8), a photomultiplier (9) provided with a high voltage (13), a second pre-amplifying circuit (10), a second comparing circuit (11) and a second shaping circuit (12) which are sequentially connected, wherein the second shaping circuit (12) is connected with the singlechip system (7);
the second voltage amplitude discrimination threshold is set in the second comparison circuit (11).
5. A neutron detection device according to claim 3, wherein:
when the first voltage amplitude discrimination threshold is 662keV of the gamma raysThe said 6 The voltage amplitude obtained by detection of the LiI scintillator (1);
the second voltage amplitude discrimination threshold is the voltage amplitude detected by the NaI (TI) scintillator (8) when the energy of the gamma rays is 662 keV;
the low-energy gamma rays refer to gamma rays with energy less than or equal to 662 keV; the high-energy gamma rays refer to gamma rays with energy greater than 662 keV.
6. A neutron detection device according to claim 3, wherein: at the said 6 A neutron response layer is arranged outside the LiI scintillator (1), and the NaI (TI) scintillator (8) is arranged close to the 6 The position of the LiI scintillator (1); the neutron response layer is used for slowing down the neutron rays to be detected into thermal neutrons, so that the neutron rays are convenient to use 6 And measuring the neutron rays by the LiI scintillator.
7. The neutron detection device of claim 6, wherein: the NaI (TI) scintillator (8) is arranged at the 6 -a middle portion of the neutron response layer outside the LiI scintillator (1).
8. The neutron detection device of claim 6, wherein: the neutron response layer is a polyethylene moderated body, and the thickness of the polyethylene moderated body is 8-10cm.
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