Geant4 analysis and optimization of a double crystal phoswich detector for beta–gamma coincidence detection

In this study, a novel phoswich detector for beta–gamma coincidence detection is designed. Unlike the triple crystal phoswich detector designed by researchers at the University of Missouri, Columbia, this phoswich detector is of the semi-well type, so it has a higher detection efficiency. The detector consists of BC-400 and NaI:Tl with decay time constants of 2.4 and 230 ns, respectively.The BC-400 scintillator detects beta particles, and the Na I:Tl cell is used for gamma detection. Geant4 simulations of this phoswich detector find that a 2-mm-thick BC-400 scintillator can absorb nearly all of the beta particles whose energies are below 700 keV. Further, for a 2.00-cmthick NaI:Tl crystal, the gamma source peak efficiency for photons ranges from a maximum of nearly 90% at 30 keV to 10% at 1 MeV. The self-absorption effect is also discussed in this paper in order to determine the carrier gas' s influence.

基于GEANT4蒙特卡罗算法的闪烁体探测器建模与优化

核设施工作场所的辐射场中往往同时存在β射线和γ射线,现有的成熟设备几乎无法同时测量混合场中的β和γ能谱,采用传统二次测量方法误差较大.针对β-γ混合场中射线互相干扰的难题,本文基于GEANT4对叠层闪烁体探测器建立蒙特卡罗模型,仿真模拟β和γ粒子在探测器中的能量沉积,研究双层和三层结构叠层闪烁体探测器中β粒子和γ光子的最优判别方案,以及不同的结构和材料对探测器甄别性能的影响.模拟结果显示,加入薄层塑料闪烁体后,三层结构的闪烁体探测器对γ粒子的误甄别率显著低于双层结构,最后比较4种不同材料的闪烁体组合对甄别性能的影响,仿真结果显示第二层采用BC444材料的甄别性能最优.

Monte-Carlo simulation to determine detector efficiency of plastic scintillating fiber

Fundamental characteristics of the plastic scintillating fiber (PSF) as a detector for electromagnetic radiation (X & γ) are obtained by GEANT4 detector simulation tool package. The detector response to radiation with energy of 10~400 keV is found out. Energy deposition as well as detector efficiency (DE) of the PSF are studied. In order to make linear array of the PSF for imaging purpose, the optimum length of fiber is also estimated.

Simulation study on performance optimization of a prototype scintillation detector for the GRANDProto35 experiment

As a proposed detector,the giant radio array for neutrino detection(GRAND)is primarily designed to discover and study the origin of ultra-high-energy cosmic rays,with ultra-high-energy neutrinos presenting the main method for detecting ultra-high-energy cosmic rays and their sources.The main principle is to detect radio emissions generated by ultra-high-energy neutrinos interacting with the atmosphere as they travel.GRAND is the largest neutrino detection array to be built in China.GRANDProto35,as the first stage of the GRAND experiment,is a coincidence array composed of radio antennas and a scintillation detector,the latter of which,as a traditional detector,is used to perform cross-validation with radio detection,thus verifying the radio detection efficiency and enabling study of the background exclusion method.This study focused on the implementation of the optimization simulation and experimental testing of the performance of the prototype scintillation detector used in GRANDProto35.A package based on GEANT4 was used to simulate the details of the scintillation detector,including the optical properties of its materials,the height of the light guide box,and position inhomogeneity.The surface of the scintillator and the reflective materials used in the detector was optimized,and the influence of light guide heights and position inhomogeneity on the energy and time resolutions of the detector was studied.According to the simulation study,the number of scintillator photoelectrons increased when changing from the polished surface to the ground surface,with the appropriate design height for the light guide box being 50 cm and the appropriate design area for the scintillator being 0.5 m^(2).The performance of the detector was tested in detail through a coincidence experiment,and the test results showed that the number of photoelectrons collected in the detector was$84 with a time resolution of~1 ns,indicating good performance.The simulation results were consistent with those obtained from the tests,which also verified the reliability of the simulation software.These studies provided a full understanding of the performance of the scintillation detector and guidance for the subsequent operation and analysis of the GRANDProto35 experimental array.

Design of hadronic calorimeter for DarkSHINE experiment

The sensitivity of the dark photon search through invisible decay final states in low-background experiments relies sig-nificantly on the neutron and muon veto efficiencies,which depend on the amount of material used and the design of the detector geometry.This paper presents the optimized design of the hadronic calorimeter(HCAL)used in the DarkSHINE experiment,which is studied using a GEANT4-based simulation framework.The geometry is optimized by comparing a traditional design with uniform absorbers to one that uses different thicknesses at different locations on the detector,which enhances the efficiency of vetoing low-energy neutrons at the sub-GeV level.The overall size and total amount of material used in the HCAL are optimized to be lower,owing to the load and budget requirements,whereas the overall performance is studied to satisfy the physical objectives.

Study on the performance of a large-size CsI detector for high energy γ-rays

The measurement of high-energy γ-rays is an important experimental method to study the giant resonance in a nucleus, c reaction in nuclear astrophysics, and so on. The performance of a large-size Cs I detector for crays detection is studied by comparison between the experimental measurements and GEANT4 simulation. The reliability of the simulated efficiency for low-energy γ-rays is verified by comparing with the experimental data. The efficiency of the Cs I detector for high-energy γ-rays was obtained by the GEANT4 simulation. The simulation shows that the detection efficiency of 20 Me V γ-rays can reach 3.8%.

The Monte-Carlo simulation on a scintillator neutron detector

A simulation of the properties of the shifting scintillator neutron detector using 6LiF/ZnS(Ag) scintillation screens is performed.The simulation results show that the light attenuation length of standard BC704 scintillator is about 0.65 mm.Its thermal neutron detection efficiency,gamma sensitivity and intrinsic spatial resolution can achieve around 50.0%,10 5and 0.18 mm(along X-axis) respectively.For the detector,air coupling position resolution is better than the silicone oil coupling.Some of the simulation results are compared with experimental results.They are in agreement.This work will be helpful for constructing neutron detector for high intensity powder diffractometer at Chinese spallation neutron source.

A large area plastic scintillation detector with 4-corner-readout

A 760 mm × 760 mm× 30 mm plastic scintillation detector viewed by photomultiplier tubes （PMTs） from four corners has been developed, and the detector has been tested with cosmic rays and γrays. A position- independent effective time Teff has been found, indicating this detector can be used as a TOF detector. The hit position can also be reconstructed by the time from the four corners.A. TOF resolution of 236 ps and a position resolution of 48 mm have been achieved, and the detection efficiency has also been investigated.

闪烁光纤阵列用于高能射线成像的可行性研究

本文通过对塑料闪烁光纤阵列在高能X或γ射线下的特性研究,分析了利用闪烁光纤阵列作为高能成像探测器的可能性。采用了基于蒙特卡罗的模拟方法,分析了闪烁光纤在高能射线下所成图像的质量,并且模拟计算了表征图像质量的信噪比(SNR),探测量子效率(DQE)以及调制传递函数(MTF)。通过这些计算得到闪烁光纤阵列有着传统闪烁屏所不具有的一些特性,把闪烁光纤的这些特点应用于高能成像中是完全可行的。

硬X射线调制望远镜卫星高能望远镜设计与验证

高能望远镜是硬X射线调制望远镜(HXMT)卫星的3台望远镜之一。其主要科学目标是在20～250keV能区进行巡天扫描,发现新的高能变源和已知源的新活动,同时监测伽马射线暴以及引力波暴电磁对应体。它的主探测器由18个直径为190mm的NaI(Tl)/CsI(Na)复合晶体探测器单体组成,具有5100cm2的几何面积,整体视场为5.7°×5.7°。高能望远镜在轨运行结果表明:探测器整体能量分辨率优于19%(在59.5keV时),时间分辨率和系统死时间优于6μs。

液闪探测器的几种n/γ甄别方法研究

利用液闪探测器研究了几种数字化波形甄别方法的n/γ甄别能力。以Am-Be源作为混合场源,用示波器对EJ-301和BC501A两种液闪探测器信号进行数字化采集,分别用上升时间法、电荷比较法、脉冲梯度分析和频率梯度分析等数字化波形甄别方法对采集的信号进行了n/γ离线甄别分析,比较了4种方法的甄别效果,并用MPD-4甄别单元从实验上验证了各方法的可靠性。结果表明:对于液闪探测器,4种数字化方法具有较好的甄别一致性和准确性,上升时间法的甄别效果最好,是实时甄别系统甄别算法的理想选择。

放射性惰性气体实时测量装置的设计与模拟研究

核反应堆在运行过程中或核应急情况下会产生^(85)Kr、^(133)Xe、^(135)Xe和^(41)Ar等放射性惰性气体,准确测量不同惰性气体的放射性活度对了解反应堆的运行状况和核应急预警均有重要意义。根据各种核素衰变发射的β、γ射线,设计并优化了可用于放射性惰性气体活度实时测量的4π双叠层闪烁体探测器。探测器的内层塑料闪烁体用于测量β射线,外层碘化铯闪烁体(CsI)用于测量γ射线,并通过β-γ的符合测量实现不同放射性核素的分辨及活度测量。针对核电放出的4种主要放射性惰性气体,基于GEANT4(GEometry ANd Tracking 4)模拟库包,研究了塑料闪烁体、CsI厚度及气体采样腔尺寸对不同核素发射的β、γ探测效率的影响;并给出该4π型双叠层闪烁体探测器的优化几何尺寸和相应探测器性能,为后续探测器的制作与测试提供参考。

Simulation of large-scale fast neutron liquid scintillation detector

Neutron background measurement is always very important for dark matter detection due to almost the same effect for the recoiled nucleus scattered off by the incident neutron and dark matter particle. For deep under-ground experiments, the flux of neutron background is so low that large-scale detection is usually necessary. In this paper, by using Geant4, the relationship between detection efficiency and volume is investigated, meanwhile, two geometrical schemes for this detection including a single large-sized detector and arrayed multi-detector are compared under the condition of the same volume. The geometrical parameters of detectors are filtrated and detection efficiencies obtained under the similar background condition of China Jingping Underground Laboratory （CJPL）. The results show that for a large-scale Gd-doped liquid scintillation detector, the detection efficiency increases with the size of detector at the beginning and then trends toward a constant. Under the condition of the same length and cross section, the arrayed multi-detector has almost similar detection performance as the single large-sized detector, while too much detector number could cause degeneration of detection performance. Considering engineering factors, such as testing, assembling and production, the 4 × 4 arrayed detector scheme is flexible and more suitable. Furthermore, the conditions for using fast and slow signal coincidence detection and the detectable lower limit of neutron energy are evaluated by simulating the light process.

Simulation study on cosmic ray background at large zenith angle based on GRANDProto35 coincidence array experiment

Neutrino detection in the 100 PeV energy region is the ultimate means of studying the origin of ultra-highenergy cosmic rays,in which the large radio detection array giant radio array for neutrino detection(GRAND)project aims to use to decipher this century-old problem.The GRANDProto35 compact array is a microform of 35 radio prototype detectors for the GRAND experiment,which verifies the reliability of GRAND performance through operation,and data analysis of the prototype detectors.As radio detectors are a novel development in recent years,and their indexes need to be verified by traditional detectors,the GRAND Cooperation Group designed and constructed the GRANDProto35 coincidence array composed of radio detectors and scintillation detectors.This study simulated the changes in detection efficiency,effective area,and event rate of cosmic rays with zenith angle based on this coincidence array.The study found that the 1017 eV energy region is sensitive to GRANDProto35 detection.When the energy exceeded 1017 eV,the array detection efficiency could reach more than 95%and the effective area was up to*29106 m2.A simulation study on cosmic ray events with large zenith angles showed that the event rate detected by the array decreased significantly with increasing zenith angle,and the event rate of cosmic rays was approximately 0.1 per day for a zenith angle of 75.This serves as the background pollution rate for neutrino observation caused by largeangle cosmic-ray events,providing an important reference for further experiments.The study results will be verified after the joint operation of the coincidence array.