- Email: [email protected]
GEANT4 Simulation of Neutron Detector for DAMPE
CHINESE ASTRONOMY AND ASTROPHYSICS Chinese Astronomy and Astrophysics 40 (2016) 474–482
GEANT4 Simulation of Neutron Detector for DAMPE† HE Ming1,2,3
MA Tao1,2
HUANG Yong-yi1,2
CHANG Jin1,2
ZANG Jing-jing1,2
ZHANG Yan1,2 WU Jian1,2
DONG Tie-kuang1,2 1 2
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008
Key Laboratory of Dark Matter and Space Astronomy, Chinese Academy of Sciences, Nanjing 210008 3
University of Chinese Academy of Sciences, Beijing 100049
Abstract In recent decades, dark matter has gradually become a hot topic in astronomical research, and the related theoretical research and experimental project are updated with each passing day. The Dark Matter Particle Explorer (DAMPE) of our country was proposed under this background. As the detected object involves high-energy electrons, appropriate methods must be taken to distinguish them from protons, in order to reduce the event probability of other charged particles (for example protons) being mistaken as electrons. The experiments show that the hadron shower of high-energy proton in BGO (Bismuth Germanium Oxide) calorimeter, which is usually accompanied with the emitting of a large number of secondary neutrons, is significantly different from the electromagnetic shower of high-energy electron. Through the detection of secondary neutron signals emerging from the bottom of BGO calorimeter, and the shower shape of incident particles in the BGO calorimeter, we can effectively distinguish whether the incident particles are high-energy protons or electrons. This paper introduces the structure and detection principle of the DAMPE neutron detector. We use the Monte-Carlo method and the GEANT4 software to simulate the signals produced by protons and electrons at the characteristic energy in the neutron detector, and finally summarize the neutron detector’s ability to distinguish protons and electrons under different electron acceptabilities. †
Supported by National Natural Science Foundation (11303105, 11303107, 11203090)
A translation of Acta Astron. Sin. Vol. 57, No. 1, pp. 1–8, 2016
Received 2015–04–30; revised version 2015–07–13
[email protected]
0275-1062/16/$-see front matter © 2016 Elsevier B.V. All rights reserved. doi:10.1016/j.chinastron.2016.10.002
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
Key words photometric
475
cosmology: dark matter—instrumentation: detector—methods:
1.
INTRODUCTION
In recent decades, dark matter has gradually become a hot topic in astronomical research, and the related theoretical research and experimental project are updated with each passing day. The Dark Matter Particle Explorer (DAMPE) of our country was proposed under this background. The scientific objectives of DAMPE are as follows: (1) By through the high-resolution wide-band space observations of high-energy electrons and γ-rays, to search and study dark matter particles, to measure indirectly their mass, annihilation cross-section, decay lifetime, and other important physical parameters, and to define the spatial distribution of dark matter particles; (2) By observing the high-energy electrons and atomic nuclei above the TeV level, to make a breakthrough as possible in the aspect of cosmic-ray origin; (3) By observing high-energy γ-rays, to make an important progress in the aspect of γ-ray astronomy, and to make a high-precision verification or detection of quantum gravitational effect[1,2] . As shown by Fig.1, from top to bottom, the payload of DAMPE is composed of the plastic scintillator, silicon-tungsten tracker, BGO (Bismuth Germanium Oxide) calorimeter, and neutron detector. The whole detection system constitutes actually a telescopic system. The plastic scintillator on the top measures the incident particles to determine whether they are charged or not; the silicon-tungsten tracker measures the track of incident particles; the BGO scintillator detector is used for measuring the shape of particle shower and the deposited total energy; and the neutron detector on the bottom is used for measuring the signal of low-energy neutron emitted from the bottom of the calorimeter, to assist the BGO calorimeter with distinguishing whether the incident particles are protons or electrons. 2. 2.1
DETECTION METHOD AND SIMULATION
Detecting Principle of Neutron Detector
In primary cosmic rays there is no neutron component. Hence, here the neutron detector is not designed for detecting the neutrons in primary cosmic rays, but the secondary neutrons produced by the interaction of hadrons (mainly protons) in cosmic rays with the detector material, and therefore to distinguish further whether the incident particles are protons or electrons. The neutron detector is composed of four pieces of plastic scintillator doped with 1% 10 B, the plastics belong to a kind of good moderator for neutrons[3] . After the elastic collision between the low-energy neutron and the hydrogen atom in the plastics, the rapid energy decay is called the moderating process. After the long time of moderation in the neutron detector, the low-energy neutrons are moderated to be thermal neutrons, then the thermal
476
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
neutrons are captured by 10 B atoms in the neutron detector[4] . Since the cross section of neutron capture reaction between the thermal neutron and the 10 B atom is very large, the nuclear reaction given by Eq.(1) happens: n + 10 B → α + 7 Li + γ .
(1)
Fig. 1 The structure of dark matter detector
The α particles produced by the nuclear reaction will deposit higher energy in the neutron detector, and will be converted into fluorescent photons in the plastic scintillator, these fluorescent photons are collected by the photomultiplier, after linear amplification, forms an electronics signal, the signal intensity has a good linear relation with the deposited energy, hence, by measuring the electronics signal, we can analyze the energy deposition in the neutron detector, and therefore the number of low-energy neutrons incident to the neutron detector. The experiments indicate that a large number of secondary hadrons (including neutrons) will be produced in the hadron shower of protons, and the secondary particles of electromagnetic shower are mainly electrons and photons, rarely neutrons, which are generally one order of magnitude less than the number of neutrons produced by protons. At the same time, in order to screen out the interference of the charged particles and γ-rays produced by high-energy electrons on the neutron detection, the electronics has set a delayed gate switch, a few microseconds after the hit signal is produced by the charged particles incident to the calorimeter, the measured signal comes mainly from the neutron capture
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
477
reaction. By the obtained energy deposition in the neutron detector, we can analyze the number of neutrons[5] , and therefore analyze the types of charged particles incident to the calorimeter by using the simulated result, then, by combing with the shower shape obtained by the BGO calorimeter[6,7] , we can distinguish effectively protons and electrons. The performance of the neutron detector satisfies the designed requirement, the lifetime of the neutron detector is determined by its parts, materials, and manufacturing technology, after the reliability design and related engineering experiments, the lifetime of the detector satisfies the experiment requirement of 3 yr. 2.2 GEANT4 Simulation and Analysis 2.2.1 An introduction to the GEANT4 software GEANT4 is an object-oriented Mont-Carlo application software package based on C++ and developed chiefly by the European Organization for Nuclear Research (CERN), it calculates mainly the transport process of particles in the detector material[8] . GEANT4 has been adopted by many large-scale experiments as the major simulation software of physical models, the comparison of its result with the real result exhibits a good consistency, therefore it has obtained wide applications. 2.2.2 The method of neutron detector simulation Now, the up-to-date version (10.0) of GEANT4 has merged most of the experimental data of neutron reaction cross-section and the physical models of high-energy particles[9] , the energy upper-limit of the simulated incident particle can attain 100 TeV, and the neutron cross-section data have included the thermal-neutron capture reaction cross-section data of 10 B atom[10] , it can simulate correctly the BGO calorimeter and neutron detector of DAMPE. 2.3 The Physical Model of Neutron Detector 2.3.1 Simulating the energy deposition of a muon in the detector When cosmic rays penetrate through the atmosphere, a large number of secondary particles are produced, in which muons can be detected in laboratory, hence, by simulating the spectrum of deposited energy when a muon is incident to the detector, we can verify the detector model built by us[11] . Fig.2 shows the track of fluorescent photons produced in the simulated detector after it is hit by a muon, the detector’s geometrical model is consistent with the real size. The spectrum of energy deposited by the incident muon and the distribution of fluorescent photons simulated by using GEANT4 are shown in Fig.3 and Fig.4, respectively.
478
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
Fig. 2 Simulation of a muon incident to the neutron detector
Fig. 3 GEANT4 simulation of energy deposition of a muon in the neutron detector
Fig. 4 GEANT4 simulation of fluorescent photon distribution
2.3.2 Building the model of electronics It is generally believed that the photon signal in the detector after being linearly amplified by the photomultiplier and amplifier is under ideal conditions, in fact, the photon frequency in the detector is fluctuated in a certain range, the amplification of the photomultiplier differs with the photon frequency, and the response of the amplifier is also not perfect, must have a certain fluctuation. Generally, after a single energy event is transmitted by the detector electronics, the obtained signal will exhibit a Gaussian distribution[12] , hence, the
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
479
model of detector electronics is generally built by comparing the simulated result with the actually measured result. It is assumed that the simulated result can approximate perfectly the spectrum of the actually measured signal output after a convolution with the Gaussian function model, the actually measured muon spectrum is shown as Fig.5.
Fig. 5 The measured muon spectrum
By assuming the Gaussian functions with different parameters, and comparing the simulated result after the convolution with the assumed Gaussian function and the measured result, we can obtain the parameters of the Gaussian function based on the minimum deviation[13,14] . The optimal comparison result is shown in Fig.6.
Fig. 6 The simulated result after the convolution with the Gaussian function as compared to the measured result
The lower panel of Fig.6 gives the absolute error of the simulated muon spectrum after the Gaussian function convolution with respect to the measured result under the optimum
480
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
condition, the maximum error is 0.12, indicating that the two curves are coincident very well, and that the built detector model can be used to simulate further other kinds of particles. 2.3.3. Simulations of electron and proton Because that averagely a proton only deposits 40% of its total energy in the calorimeter, and that in practical experiments, we compare only the events of identical energy deposition, hence, we select the electron event of 500 GeV and the proton event of 1.4 TeV to make simulations, and select the events of identical deposited energy in the calorimeter. For these events, the photon distribution can be obtained from the number of the photons produced in the neutron detector, then the output signal spectrum can be obtained by using the electronics model in Subsection 2.3.2, the results are given in Figs.7∼8.
Fig. 7 The electron’s output signal from the neutron detector
Fig. 8 The proton’s output signal from the neutron detector
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
3.
481
DATA ANALYSIS
The purpose of the electron and proton simulations is to obtain the ability of the neutron detector for distinguishing electrons and protons, to distinguish effectively electrons nd protons is the primarily designed requirement on the neutron detector. Comparing Fig.7 with Fig.8, we can find that for the same deposited energy in the BGO calorimeter, the output spectra of the electron and proton in the neutron detector are obviously different, now to define the electron acceptability to be: Electron acceptability =
The number of selected electron events , The number of total electron events
(2)
and the proton rejection power[15] of neutron detector to be: Rejection power =
Accepted electrons , The protons mistaken as electrons
(3)
then, from the simulated result in Subsection 2.3.3, we can obtain the relationship between the proton rejection power and the electron acceptability as shown by Fig.9. From the rejection power curve in Fig.9, we can find that when the electron acceptability of neutron detector is 50%, the proton rejection power is 56. This indicates that when the neutron detector can satisfy a certain electron acceptability, it can distinguish effectively electrons and protons.
Fig. 9 The rejection power of neutron detector
4.
CONCLUSION
It is difficult to detect cosmic high-energy electrons, to distinguish electrons from the cosmicray background needs special detection techniques[16] . The neutron detector is designed just
482
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
for distinguishing protons and electrons. Using GEANT4, this paper has simulated the spectrum of energy deposited by a muon in the neutron detector and the distribution of fluorescent photons, and verified the physical model and electronics model in combination with the actually measured result. Then, with the verified physical model and electronics model, we have made the simulations of electron and proton, the simulated results indicate that when the electron acceptability of neutron detector is 50%, its proton rejection power is 56. This shows that under a certain electron acceptability, the neutron detector can distinguish effectively electrons and protons. References 1
Cai M. S., Guo J. H., Xie M. G., AcASn, 2013, 54, 467
2
Cai M. S., Guo J. H., Xie M. G., ChA&A, 2014, 38, 200,
3
Chang L., Liu L. X., Wang H. W. et al., Nuclear Technology, 2015, 38, 50403
4
Reiter A. J. H., Differential Photoneutron Cross Sections of Light Nuclei for Neutron Dosimetry, Glasgow: University of Glagow, 2004
5
Zhang G. Q., Li P. B., Li C. Y., et al., Nuclear Technology, 2015, 38, 10501
6
Guo J. H., Cai M. S., Hu Y. M., et al., AcASn, 2012, 53, 318
7
Guo J. H., Cai M. S., Hu Y. M., et al., ChA&A, 2012, 36, 318
8
Du L., The Monte-Carlo simulation and experimental Measurement Based on the 6 Li Neutron Detector, Shanghai: Shanhai Institute of Applied Physics, Chinese Academy of Sciences, 2014
9
Yue K., Xu S. S., Liang J. J., et al., Nuclear physics Review, 2010, 27, 445
10
Wu C., Zhang Q., Sun Z. J., et al., Nuclear physics Review, 2012, 29, 173
11
Wolverton M., SciAm, 2007, 297, 26
12
Xie Y. G., Chen C.,Wang M., et al., Particle Detector and Data Aquisition, Beijing: Science Press, 2003
13
Zhang L., Guo J. H., Zhang Y. Q., AcASn, 2014, 55, 522
14
Zhang L., Guo J. H., Zhang Y. Q., ChA&A, 2015, 39, 380
15
Drake D. M., Feldman W. C., Hurlbut C., NIMPR, 1986, 247, 576
16
Chang J., Engineering Research–Engineering in an interdisciplinary perspective, 2010, 2, 95
GEANT4 Simulation of Neutron Detector for DAMPE† HE Ming1,2,3
MA Tao1,2
HUANG Yong-yi1,2
CHANG Jin1,2
ZANG Jing-jing1,2
ZHANG Yan1,2 WU Jian1,2
DONG Tie-kuang1,2 1 2
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008
Key Laboratory of Dark Matter and Space Astronomy, Chinese Academy of Sciences, Nanjing 210008 3
University of Chinese Academy of Sciences, Beijing 100049
Abstract In recent decades, dark matter has gradually become a hot topic in astronomical research, and the related theoretical research and experimental project are updated with each passing day. The Dark Matter Particle Explorer (DAMPE) of our country was proposed under this background. As the detected object involves high-energy electrons, appropriate methods must be taken to distinguish them from protons, in order to reduce the event probability of other charged particles (for example protons) being mistaken as electrons. The experiments show that the hadron shower of high-energy proton in BGO (Bismuth Germanium Oxide) calorimeter, which is usually accompanied with the emitting of a large number of secondary neutrons, is significantly different from the electromagnetic shower of high-energy electron. Through the detection of secondary neutron signals emerging from the bottom of BGO calorimeter, and the shower shape of incident particles in the BGO calorimeter, we can effectively distinguish whether the incident particles are high-energy protons or electrons. This paper introduces the structure and detection principle of the DAMPE neutron detector. We use the Monte-Carlo method and the GEANT4 software to simulate the signals produced by protons and electrons at the characteristic energy in the neutron detector, and finally summarize the neutron detector’s ability to distinguish protons and electrons under different electron acceptabilities. †
Supported by National Natural Science Foundation (11303105, 11303107, 11203090)
A translation of Acta Astron. Sin. Vol. 57, No. 1, pp. 1–8, 2016
Received 2015–04–30; revised version 2015–07–13
[email protected]
0275-1062/16/$-see front matter © 2016 Elsevier B.V. All rights reserved. doi:10.1016/j.chinastron.2016.10.002
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
Key words photometric
475
cosmology: dark matter—instrumentation: detector—methods:
1.
INTRODUCTION
In recent decades, dark matter has gradually become a hot topic in astronomical research, and the related theoretical research and experimental project are updated with each passing day. The Dark Matter Particle Explorer (DAMPE) of our country was proposed under this background. The scientific objectives of DAMPE are as follows: (1) By through the high-resolution wide-band space observations of high-energy electrons and γ-rays, to search and study dark matter particles, to measure indirectly their mass, annihilation cross-section, decay lifetime, and other important physical parameters, and to define the spatial distribution of dark matter particles; (2) By observing the high-energy electrons and atomic nuclei above the TeV level, to make a breakthrough as possible in the aspect of cosmic-ray origin; (3) By observing high-energy γ-rays, to make an important progress in the aspect of γ-ray astronomy, and to make a high-precision verification or detection of quantum gravitational effect[1,2] . As shown by Fig.1, from top to bottom, the payload of DAMPE is composed of the plastic scintillator, silicon-tungsten tracker, BGO (Bismuth Germanium Oxide) calorimeter, and neutron detector. The whole detection system constitutes actually a telescopic system. The plastic scintillator on the top measures the incident particles to determine whether they are charged or not; the silicon-tungsten tracker measures the track of incident particles; the BGO scintillator detector is used for measuring the shape of particle shower and the deposited total energy; and the neutron detector on the bottom is used for measuring the signal of low-energy neutron emitted from the bottom of the calorimeter, to assist the BGO calorimeter with distinguishing whether the incident particles are protons or electrons. 2. 2.1
DETECTION METHOD AND SIMULATION
Detecting Principle of Neutron Detector
In primary cosmic rays there is no neutron component. Hence, here the neutron detector is not designed for detecting the neutrons in primary cosmic rays, but the secondary neutrons produced by the interaction of hadrons (mainly protons) in cosmic rays with the detector material, and therefore to distinguish further whether the incident particles are protons or electrons. The neutron detector is composed of four pieces of plastic scintillator doped with 1% 10 B, the plastics belong to a kind of good moderator for neutrons[3] . After the elastic collision between the low-energy neutron and the hydrogen atom in the plastics, the rapid energy decay is called the moderating process. After the long time of moderation in the neutron detector, the low-energy neutrons are moderated to be thermal neutrons, then the thermal
476
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
neutrons are captured by 10 B atoms in the neutron detector[4] . Since the cross section of neutron capture reaction between the thermal neutron and the 10 B atom is very large, the nuclear reaction given by Eq.(1) happens: n + 10 B → α + 7 Li + γ .
(1)
Fig. 1 The structure of dark matter detector
The α particles produced by the nuclear reaction will deposit higher energy in the neutron detector, and will be converted into fluorescent photons in the plastic scintillator, these fluorescent photons are collected by the photomultiplier, after linear amplification, forms an electronics signal, the signal intensity has a good linear relation with the deposited energy, hence, by measuring the electronics signal, we can analyze the energy deposition in the neutron detector, and therefore the number of low-energy neutrons incident to the neutron detector. The experiments indicate that a large number of secondary hadrons (including neutrons) will be produced in the hadron shower of protons, and the secondary particles of electromagnetic shower are mainly electrons and photons, rarely neutrons, which are generally one order of magnitude less than the number of neutrons produced by protons. At the same time, in order to screen out the interference of the charged particles and γ-rays produced by high-energy electrons on the neutron detection, the electronics has set a delayed gate switch, a few microseconds after the hit signal is produced by the charged particles incident to the calorimeter, the measured signal comes mainly from the neutron capture
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
477
reaction. By the obtained energy deposition in the neutron detector, we can analyze the number of neutrons[5] , and therefore analyze the types of charged particles incident to the calorimeter by using the simulated result, then, by combing with the shower shape obtained by the BGO calorimeter[6,7] , we can distinguish effectively protons and electrons. The performance of the neutron detector satisfies the designed requirement, the lifetime of the neutron detector is determined by its parts, materials, and manufacturing technology, after the reliability design and related engineering experiments, the lifetime of the detector satisfies the experiment requirement of 3 yr. 2.2 GEANT4 Simulation and Analysis 2.2.1 An introduction to the GEANT4 software GEANT4 is an object-oriented Mont-Carlo application software package based on C++ and developed chiefly by the European Organization for Nuclear Research (CERN), it calculates mainly the transport process of particles in the detector material[8] . GEANT4 has been adopted by many large-scale experiments as the major simulation software of physical models, the comparison of its result with the real result exhibits a good consistency, therefore it has obtained wide applications. 2.2.2 The method of neutron detector simulation Now, the up-to-date version (10.0) of GEANT4 has merged most of the experimental data of neutron reaction cross-section and the physical models of high-energy particles[9] , the energy upper-limit of the simulated incident particle can attain 100 TeV, and the neutron cross-section data have included the thermal-neutron capture reaction cross-section data of 10 B atom[10] , it can simulate correctly the BGO calorimeter and neutron detector of DAMPE. 2.3 The Physical Model of Neutron Detector 2.3.1 Simulating the energy deposition of a muon in the detector When cosmic rays penetrate through the atmosphere, a large number of secondary particles are produced, in which muons can be detected in laboratory, hence, by simulating the spectrum of deposited energy when a muon is incident to the detector, we can verify the detector model built by us[11] . Fig.2 shows the track of fluorescent photons produced in the simulated detector after it is hit by a muon, the detector’s geometrical model is consistent with the real size. The spectrum of energy deposited by the incident muon and the distribution of fluorescent photons simulated by using GEANT4 are shown in Fig.3 and Fig.4, respectively.
478
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
Fig. 2 Simulation of a muon incident to the neutron detector
Fig. 3 GEANT4 simulation of energy deposition of a muon in the neutron detector
Fig. 4 GEANT4 simulation of fluorescent photon distribution
2.3.2 Building the model of electronics It is generally believed that the photon signal in the detector after being linearly amplified by the photomultiplier and amplifier is under ideal conditions, in fact, the photon frequency in the detector is fluctuated in a certain range, the amplification of the photomultiplier differs with the photon frequency, and the response of the amplifier is also not perfect, must have a certain fluctuation. Generally, after a single energy event is transmitted by the detector electronics, the obtained signal will exhibit a Gaussian distribution[12] , hence, the
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
479
model of detector electronics is generally built by comparing the simulated result with the actually measured result. It is assumed that the simulated result can approximate perfectly the spectrum of the actually measured signal output after a convolution with the Gaussian function model, the actually measured muon spectrum is shown as Fig.5.
Fig. 5 The measured muon spectrum
By assuming the Gaussian functions with different parameters, and comparing the simulated result after the convolution with the assumed Gaussian function and the measured result, we can obtain the parameters of the Gaussian function based on the minimum deviation[13,14] . The optimal comparison result is shown in Fig.6.
Fig. 6 The simulated result after the convolution with the Gaussian function as compared to the measured result
The lower panel of Fig.6 gives the absolute error of the simulated muon spectrum after the Gaussian function convolution with respect to the measured result under the optimum
480
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
condition, the maximum error is 0.12, indicating that the two curves are coincident very well, and that the built detector model can be used to simulate further other kinds of particles. 2.3.3. Simulations of electron and proton Because that averagely a proton only deposits 40% of its total energy in the calorimeter, and that in practical experiments, we compare only the events of identical energy deposition, hence, we select the electron event of 500 GeV and the proton event of 1.4 TeV to make simulations, and select the events of identical deposited energy in the calorimeter. For these events, the photon distribution can be obtained from the number of the photons produced in the neutron detector, then the output signal spectrum can be obtained by using the electronics model in Subsection 2.3.2, the results are given in Figs.7∼8.
Fig. 7 The electron’s output signal from the neutron detector
Fig. 8 The proton’s output signal from the neutron detector
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
3.
481
DATA ANALYSIS
The purpose of the electron and proton simulations is to obtain the ability of the neutron detector for distinguishing electrons and protons, to distinguish effectively electrons nd protons is the primarily designed requirement on the neutron detector. Comparing Fig.7 with Fig.8, we can find that for the same deposited energy in the BGO calorimeter, the output spectra of the electron and proton in the neutron detector are obviously different, now to define the electron acceptability to be: Electron acceptability =
The number of selected electron events , The number of total electron events
(2)
and the proton rejection power[15] of neutron detector to be: Rejection power =
Accepted electrons , The protons mistaken as electrons
(3)
then, from the simulated result in Subsection 2.3.3, we can obtain the relationship between the proton rejection power and the electron acceptability as shown by Fig.9. From the rejection power curve in Fig.9, we can find that when the electron acceptability of neutron detector is 50%, the proton rejection power is 56. This indicates that when the neutron detector can satisfy a certain electron acceptability, it can distinguish effectively electrons and protons.
Fig. 9 The rejection power of neutron detector
4.
CONCLUSION
It is difficult to detect cosmic high-energy electrons, to distinguish electrons from the cosmicray background needs special detection techniques[16] . The neutron detector is designed just
482
HE Ming et al. / Chinese Astronomy and Astrophysics 40 (2016) 474–482
for distinguishing protons and electrons. Using GEANT4, this paper has simulated the spectrum of energy deposited by a muon in the neutron detector and the distribution of fluorescent photons, and verified the physical model and electronics model in combination with the actually measured result. Then, with the verified physical model and electronics model, we have made the simulations of electron and proton, the simulated results indicate that when the electron acceptability of neutron detector is 50%, its proton rejection power is 56. This shows that under a certain electron acceptability, the neutron detector can distinguish effectively electrons and protons. References 1
Cai M. S., Guo J. H., Xie M. G., AcASn, 2013, 54, 467
2
Cai M. S., Guo J. H., Xie M. G., ChA&A, 2014, 38, 200,
3
Chang L., Liu L. X., Wang H. W. et al., Nuclear Technology, 2015, 38, 50403
4
Reiter A. J. H., Differential Photoneutron Cross Sections of Light Nuclei for Neutron Dosimetry, Glasgow: University of Glagow, 2004
5
Zhang G. Q., Li P. B., Li C. Y., et al., Nuclear Technology, 2015, 38, 10501
6
Guo J. H., Cai M. S., Hu Y. M., et al., AcASn, 2012, 53, 318
7
Guo J. H., Cai M. S., Hu Y. M., et al., ChA&A, 2012, 36, 318
8
Du L., The Monte-Carlo simulation and experimental Measurement Based on the 6 Li Neutron Detector, Shanghai: Shanhai Institute of Applied Physics, Chinese Academy of Sciences, 2014
9
Yue K., Xu S. S., Liang J. J., et al., Nuclear physics Review, 2010, 27, 445
10
Wu C., Zhang Q., Sun Z. J., et al., Nuclear physics Review, 2012, 29, 173
11
Wolverton M., SciAm, 2007, 297, 26
12
Xie Y. G., Chen C.,Wang M., et al., Particle Detector and Data Aquisition, Beijing: Science Press, 2003
13
Zhang L., Guo J. H., Zhang Y. Q., AcASn, 2014, 55, 522
14
Zhang L., Guo J. H., Zhang Y. Q., ChA&A, 2015, 39, 380
15
Drake D. M., Feldman W. C., Hurlbut C., NIMPR, 1986, 247, 576
16
Chang J., Engineering Research–Engineering in an interdisciplinary perspective, 2010, 2, 95