束流实验中不同尺寸塑料闪烁体的时间特性

北京谱仪(BESⅢ)中的飞行时间探测器将采用长2.3m宽6cm的长条形塑料闪烁体. 利用北京高能物理研究所的实验束流对铝膜包装的不同厚度闪烁体的本征时间分辨进行了研究,给出了4cm, 5cm和6cm闪烁体的时间分辨, 而且用蒙特卡罗模拟做了比较, 结果表明5cm厚的闪烁体具有最佳性能.     

环形正负电子对撞机带电粒子鉴别的飞行时间探测器

环形正负电子对撞机(circular electron-positron collider, CEPC)通过d E/dx的测量进行长寿命带电粒子的鉴别,要求对d E/dx的测量达到约3%的精度.但d E/dx的测量对带电粒子π/K,π/P和K/P各有一个分辨盲区,对应的横动量分别为1 GeV/c, 1.6 GeV/c和2 GeV/c.一种解决方案是采用高精度飞行时间(time of flight, TOF)探测器填补分辨盲区,探测器系统的时间分辨要求小于50 ps.针对这一要求本文提出一种小颗粒飞行时间探测器,具体方案为采用小块塑料闪烁体(1 cm×1 cm×0.3 cm)侧面耦合硅光电倍增管读出.介绍了该探测器的构建以及利用90 Sr电子准直源和高速波形采集电子学对该探测器的性能标定.结果显示,采用恒比定时法,该探测器的时间分辨约为48 ps,可以满足CEPC对飞行时间探测器的要求.     

BESⅢ端盖TOF探测器的研制

针对BESⅢ端盖TOF的研制方案, 设计和制作了特殊构型的闪烁探测器. 研究了光电倍增管(R5924)和塑料闪烁体(BC404, BC408, EJ204)的性能. 测量了几种包装材料对单个闪烁探测器模块光收集和本征时间分辨的影响. 使用800MeV实验电子束对探测器模块的测量结果显示, 采用EJ204和BC404晶体其时间分辨小于80ps; 采用ESR材料包装可获得较大的输出信号, 提高了探测器的性能.     

用于中子位置灵敏探测器的SiPM性能研究

为满足中国散裂中子源(China Spallation Neutron Source,CSNS)工程材料衍射谱仪的探测器需求,CSNS探测器组设计并研制了基于硅光电倍增管(Silicon Photomultiplier,SiPM)读出的闪烁体探测器。本工作针对该探测器,选取了Sensl MicroFJ-30035-TSV和Hamamatsu S13363-3050NE-16两种型号的SiPM,开展了其击穿电压、增益、温度特性、暗计数率等关键性能的测试。测试结果显示,两者单光子分辨能力,增益、暗计数率等性能均可满足当前闪烁体探测器需求,相同过偏压下,前者增益高于后者,且Hamamatsu SiPM增益对温度更敏感。测试了两SiPM的温度补偿系数分别为22.0 mV/℃(Sens1)和53.6 mV/℃(Hamamatsu),为后续SiPM温度补偿电路设计奠定了基础。利用研制的探测器工程样机,在CSNS BL09下测试了两种SiPM读出的探测器对2.8 ?中子探测效率分别为76%和68%,为目标探测器及同类型探测器的SiPM选型提供了参考。     

一种基于SiPM的新型起始时间探测器研制

本文介绍了一种新型起始时间探测器的研制。该探测器的灵敏面积为60 mm×60 mm,利用120根直径为1 mm的塑料闪烁光纤分成两层错位紧致排布,且上下相邻的3根光纤作为一个探测单元,每个探测单元均采用硅光电倍增管从双端读出信号。采用90Sr放射源对单根光纤进行了性能测试,结果表明,闪烁光沿着光纤方向的有效传播速度约为17 cm/ns,对应的时间分辨优于600 ps。此外,利用中国科学院近代物理研究所第二条放射性束流线（RIBLL2）提供的240 MeV/u的15N次级束研究了该探测器的性能。束流测试结果表明:该探测器的时间分辨为（150±15）ps,纵向位置分辨为（1.8±0.2）cm,并且结合该探测器以及RIBLL2束流线外靶实验终端上的其他探测器,可以对实验中产生的5 ≤ Z ≤ 8的各种同位素进行非常好的粒子鉴别。     

多像素光子计数器(MPPC)的性能测试

多像素光子计数器(Multi Pixel Photo Counter,简称MPPC)是近几年发展起来的一种新型信号读出设备.为了对这种设备制作的闪烁探测器有较深入的了解和认知,本文配合塑料闪烁体,与MPPC制成塑料闪烁探测器,对利用这种新型的光子计数器做成的探测器进行了研究.利用它测试了塑料闪烁体的时间和位置分辨率,将这方面数据与之前常用的配有光电倍增管的闪烁探测器的数据进行了比较,能够了解到用MPPC与塑料闪烁体做成的闪烁探测器在时间分辨和位置分辨方面能够达到实验的要求.在信价比和几何大小方面,MPPC优于光电倍增管,因此利用MPPC将在实验方面带来很大的优越性,为实验研究提供更大的方便.     

BESⅢ端盖TOF本征时间分辨的MC模拟

BESⅢ飞行时间探测器(端盖部分)由2×48个塑料闪烁探测器模块构成. 采用Monte Carlo模拟软件包Geant4，对该探测器测量高能带电粒子的性能进行了模拟研究. 文章讨论了最小电离粒子击中闪烁体不同位置，以及闪烁体形状，闪烁体表面覆盖材料对本征时间分辨的影响，给出了详细的模拟结果，并与宇宙线测试结果进行了比较. 为该探测器研制和工程设计提供必要的参考数据.     

快响应塑料闪烁体EJ-232的时间特性研究

在核反应时间过程测量系统中,闪烁体主要用于将中子转换为便于记录的可见光.EJ-232塑料闪烁体的主要特点是响应快、衰减时间短,利用其进行中子一光转换可提高系统的时间分辨.利用波长为263nm的激光激发闪烁体对其时间特性进行了测量,闪烁体尺寸为φ6 mm×1 mm和φ6 ram×2 mm.测量结果表明,EJ-232塑料闪...     

高时间分辨MRPC的位置灵敏读出方法

根据MRPC工作机制和高时间分辨的特性, 研制一种位置灵敏MRPC原型及读出方法. 该探测器具有10个220μm气隙, 有效探测面积为20cm×20cm. 前端电子学采用专用ASIC芯片, 具有快时间响应和输入电荷-输出信号宽度的转换功能. 采取同时读取信号传输时间差和感应信号分布的方法实现两维读出. 对该探测器性能的束流测试结果显示: 沿着读出条方向及其垂直方向的位置分辨分别为4.5mm和1.6mm, 其时间分辨达到63ps, 探测效率>95%.     

BESⅢ端盖TOF时间分辨的束流测试

使用800MeV的电子束对BESⅢ端盖飞行时间探测器(TOF)模块的性能进行测试. 研究了塑料闪烁体的包装材料、光电倍增管(PMT)的工作电压、电子束入射位置对单个TOF模块的本征时间分辨的影响，并给出了测量时间与信号幅度和粒子击中位置的修正方法. 实验结果显示:使用Tyvek纸包装，闪烁体在安装PMT的一端有45°斜面, 电子击中在TOF模块不同位置其本征时间分辨在70—90ps范围内.     

超重反冲余核时间探测器性能测试

介绍了一种铝制内椭球面反射镜闪烁薄膜探测器,对其探测效率、光收集效率和时间性能的测试. 结果分析表明采用1 μm厚的BC498闪烁薄膜探测器测量实验中超重反冲余核, 探测效率接近100％, 时间分辨好于200 ps, 其性能满足超重反冲余核时间测量的要求. A thin plastic scintillator film detector with an inner ellipsoidal reflection mirror made of aluminum is introduced. Detection efficiency and light collection efficiency of the detector have been investigated. The time resolution of the detector has been also studied. The testing results show that the detection efficiency of BC498 with the thickness of 1 micron to be used in the coming superheavy synthesis experiments is approximately 100%, and the time resolution is better than 200 ps (σ). The performances of the thin plastic scintillator film detector meet the requirements for the time measurement of the superheavy element synthesis.     

Simulation of 12C+12C elastic scattering at high energy by using the Monte Carlo method

The Monte Carlo method is used to simulate the ¹²C+¹²C reaction process. Taking into account the size of the incident ¹²C beam spot and the thickness of the ¹²C target, the distributions of scattered ¹²C on the MWPC and the CsI detectors at a detective distance have been simulated. In order to separate elastic scattering from the inelastic scattering with 4.4 MeV excited energy, we set several variables: the kinetic energy of incident ¹²C, the thickness of the ¹²C target, the ratio of the excited state, the wire spacing of the MWPC, the energy resolution of the CsI detector and the time resolution of the plastic scintillator. From the simulation results, the preliminary establishment of the experiment system can be determined to be that the beam size of the incident ¹²C is φ 5 mm, the incident kinetic energy is 200-400 A MeV, the target thickness is 2 mm, the ratio of the excited state is 20%, the ight distance of scattered ¹²C is 3 m, the energy resolution of the CsI detectors is 1%, the time resolution of the plastic scintillator is 0.5%, and the size of the CsI detectors is 7 cm×7 cm, and we need at least 16 CsI detectors to cover a 0° to 5° angular distribution.     

An experimental study of the relative response of plastic scintillators to photons and beta particles

A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6 keV to 1.332 MeV and a Ni-63 beta source with a maximum energy of 66 keV. Scintillator thicknesses ranged from 10 μm to 2500 μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. These experimental findings were used to empirically determine the optimum thickness of scintillator material with which to build a low energy beta detector which discriminates against high energy gamma photons in a mixed radiation field environment.     

利用ICCD定位宇宙线来测量探测器时间分辨的方法研究

本研究采用双层150 mm×150 mm闪烁条阵列定位宇宙线的入射和出射位置. 阵列信号光使用波移光纤吸收传输,在ICCD相机前插入前置像增强器,使信号光延迟大于200 ns, 使ICCD可以由外部高速触发信号控制,有效记录随机触发事例.该宇宙线定位系统可以同时多点密集测量 通用探测器测试平台的时间分辨和闪烁光的渡越时间.该新方法与传统时间分辨测量方法相比提高了30倍以上 的效率.实验结果显示:时间探测器的时间分辨好于200 ps,满足通用探测器测试平台的设计要求.     

A capture-gated fast neutron detection method

To address the problem of the shortage of neutron detectors used in radiation portal monitors(RPMs),caused by the ~3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm × 1 cm × 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture γ-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register γ-rays. This design removes the volume competing relationship in traditional ~3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66% ± 1.22% has been achieved with a 40.4 cm × 40.4cm × 20 cm overall detector volume. This detector can measure both neutrons and γ-rays simultaneously. A small detector(20.2 cm × 20.2 cm × 20 cm) demonstrated a 3.3 % false alarm rate for a ~(252)Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 s measurement time. It also demonstrated a very low(0.06%) false alarm rate for a 3.21 × 10~5 Bq ~(137)Cs source. This detector offers a potential single-detector replacement for both neutron and the γ-ray detectors in RPM systems.     

Cosmic ray test for a T0 detector

The endcap of time-of-flight (ETOF) detector in BES (Beijing Spectrometer) III is planned to be upgraded by using multi-gap resistive plate chambers (MRPCs) and the designed time resolution of the MRPCs is around 50 ps. Thus a time-zero (T0) detector needs to be built to offer a high quality reference time for the MRPCs beam test. So a T0 detector is built using plastic scintillator tiles (BC420) to couple with four fast phototubes (PMTs, Hamamatsu H6533). The timing properties of the detector is studied by using a cosmic ray test and factors related to the time resolution, such as plastic scintillator size, readout mode and angle effects, are discussed. T0 detector timing resolutions of ～41-62 ps are achieved, which means that the T0 detector can be used in the MRPC beam test.     

Compton-Polarimeter für 2 MeV-Bremsstrahlung

A polarimeter for bremsstrahlung must simultaneously perform two functions: it must select photons within a small energy interval out of the continuous bremsstrahlung spectrum and it must measure the polarization of these photons. The polarimeter depends on the polarization sensitivity of the Compton process with a 5 mm Si(Li-drift) detector as scatterer and a plastic scintillator as photon detector. To improve the energy resolution of the polarimeter a second 0,5 mm Si(Li-drift) detector behind the scatterer has been placed in anticoincidence with the scatterer.     

用于软X射线图像诊断的CMOS探测系统

通过将闪烁体光纤面板与CMOS图像传感器耦合,研制了在线诊断X射线图像的CMOS探测系统。通过XOP软件计算,确定了响应能区为1~10keV的CsI闪烁体厚度为30μm。在微点X射线源平台上,基于标准的Typ 18-d型分辨率板对CMOS探测系统的空间分辨能力进行了实验测试,结果为60μm。在神光Ⅲ原型激光装置上,利用该套CMOS探测系统在流体力学不稳定性与混合实验中对钛背光源的光谱进行了诊断,获得了清晰的类氢和类氦光谱图像。数据分析显示,实测的谱分辨为442,与理论分析符合较好。CMOS探测系统小巧轻便,性价比高,适合各大高校与科研院所用于在线诊断软X射线图像。