室温半导体CdZnTe(CdTe)探测器性能综述

CdZnTe(CdTe)探测器是近年来迅速发展的新型半导体探测器,具有体积小、分辨率高、可在室温下工作等优点。由于探测器晶体内电荷收集不完全,导致所测的γ谱会产生低能尾巴,从而增加了谱解析的困难,需要进行新的解谱算法研究。介绍了其基本性能、电极设计、γ谱解析方法和发展趋势。     

人工神经网络解析CdZnTe探测器γ谱

半导体CdZnTe探测器具有体积小、分辨率高、可在室温下工作等优点而适用于野外便携式γ谱仪系统。由于CdZnTe晶体内电荷收集不完全导致γ谱产生低能尾巴,因而增加了常规谱解析的难度。采用了人工神经网络方法进行全γ谱法定性定量分析,可以充分利用γ谱所含信息,迅速准确地得出结果,避免了采用常规谱解析方法时低能尾巴对峰形拟合的影响。     

平面型CdZnTe探测器的能谱特性模拟

CdZnTe(CZT)探测器是一种高原子序数的化合物半导体探测器，具有体积小、探测效率高、可在常温环境使用等特点，广泛应用于X、γ射线探测领域。为了更好地研究CZT探测器能谱特性的影响因素，通过Geant4软件建立探测器几何模型，模拟计算CZT晶体的本征探测效率和吸收率；根据Hecht公式计算电荷收集效率，通过收集晶体中的沉积能量和位置信息得到γ射线能谱；通过分析晶体的物理特性，探索其对探测器性能的影响。模拟计算结果表明：电荷收集不完整是影响探测器能谱性能的重要因素，当能量低于50 keV时，γ射线谱基本不受空穴尾迹的影响，而能量在50～100 keV的γ射线能谱受空穴尾迹的影响较为明显，高于100 keV的γ射线能谱受空穴尾迹的影响逐渐加重。通过增加偏压的方式可以降低空穴尾迹对能谱的影响，同时偏压的增加会使峰位产生偏移，偏移程度受最大电荷收集效率的影响。     

CdZnTe像素探测器的制备与表征

本文采用CdZnTe单晶制成像素探测器,并对其能谱响应特性及均匀性进行了系统表征。通过I-V和能谱响应测试,测定了晶体的电阻率和载流子迁移率与寿命的积,并用红外透过显微成像观察了晶体内Te夹杂的分布特性。采用光刻、剥离和真空蒸镀技术,在CdZnTe晶片上制备了8×8的像素电极,用丝网印刷和贴片技术通过导电银胶实现像素电极与读出电路的准确连接,制备出CdZnTe像素探测器。对像素探测器的测试表明,-300V下单像素最大漏电流小于0.7nA,对241 Am 59.5keV的能量分辨率可达5.6%,优于平面探测器。进一步分析了晶体内Te夹杂等缺陷对探测器漏电流和能谱响应特性的影响规律,结果表明,Te夹杂的聚集会显著增加漏电流,并降低探测器的能量分辨率。     

用于空间探测的新型弗里希栅碲锌镉探测器

研究用于空间探测的新型弗里希栅碲锌镉探测器。选择CdZnTe晶体尺寸为5mm×5mm×5mm的平面结构探测器，通过改进电极结构，采用电容弗里希栅构成只收集电子的单电荷载流子探测器单元，从而使电子对信号脉冲起主要贡献，而去除由于空穴的陷获对脉冲产生的影响。     

基于蒙特卡罗方法模拟计算CZT探测器的γ能谱

在了解CZT探测器结构的基础上,用蒙特卡罗程序MCNP对探测器中光子输运过程进行模拟计算,得到光子在探测器中沉积能量的大小及位置信息.编程读取这些信息并计算出γ射线能谱.考虑到所用探测器的实际情况,提出了一个简化的海克公式计算电荷收集效率,对法诺因子及噪声的影响进行了展宽处理.计算得到的γ能谱与实验谱基本一致,全能峰的峰位和低能尾迹得到较好地模拟.     

基于Monte-Carlo模拟和峰形拟合的CdZnTe探测器G(E)函数简便计算方法研究

提出了一种简便的CdZnTe探测器能谱-剂量转换函数(G(E)函数)的计算方法。峰形拟合函数被用于表征CdZnTe探测器对γ射线的低能拖尾,峰形拟合函数的参数通过实验测量获取,并通过拟合得到其随能量变化的关系。Monte-Carlo模拟计算得到的探测器理想沉积谱,经峰形拟合函数卷积得到了修正的模拟能谱,修正的模拟能谱与实际测量能谱吻合较好。基于修正的模拟能谱计算得到了CdZnTe探测器的G(E)函数。标准辐射场中的实验结果表明,用G(E)函数加权积分计算的周围剂量当量率与约定真值基本一致。     

基于高能γ源的CdZnTe成像探测器极化效应研究

应用第一类边界条件泊松方程,推导了碲锌镉(CdZnTe)探测器晶体内部电势分布,研究了CdZnTe探测器在¹³⁷Cs高能γ源成像探测过程中的极化效应。数值计算与实验结果表明：在低辐射注量率条件下,即CdZnTe晶体内部载流子电荷密度较低时,内部电势分布主要受外加偏压影响,晶体内部电势与偏压为线性关系,电场呈均匀分布。在高辐射注量率条件下,即晶体内部载流子电荷密度较高时,内部电势分布出现极化区域,电场分布发生扭曲,电子载流子向辐照区域外侧迁移,形成辐照中心无信号而辐照边缘区域仍有响应信号的极化探测图像。极化效应造成CdZnTe探测器探测性能严重退化,辐照边缘区域像素事件计数下降约70%。     

CZT探测器的峰形拟合

作为一种中等分辨率且能在常温下使用的小型探测器，CZT特别适用于便携式现场测量设备中。由于载流子传输过程中发生电荷不完全收集及空穴俘获等效应，致使CZT探测器输出谱的全能峰偏离了理想的高斯峰形而伴有显著低能拖尾。对于标准包装的含铀材料，易于采用235U的186keY单一能峰进行解谱分析（丰度计原理）；对于不规则样品，在包装物对低能X和γ射线吸收不太显著的情况下，CZT能谱，特别是低能部分的能峰，相互重叠严重，在解谱过程中需要合适的峰形拟合算法。     

平面型碲锌镉(CZT)室温探测器的噪声和性能

CdZnTe(CZT)探测器是近年来迅速发展的新型半导体探测器,具有体积小、分辨率高、可在室温下工作等优点。论文通过分析探测器的噪声组成,并经过实验数据分析,证明了影响探测器性能的主要因素是探测器晶体内电荷收集不完全,并为探测仪器设计时的成形时间选择提供了参考。     

CdZnTe quasi-hemispherical detector for gamma–neutron detection

Quasi-hemispherical CdZnTe detector was manufactured successfully to fully understand the performance in the mixed gamma–neutron detection field. Together with the software of COMSOL, Geant4, and Matlab, the detector structure has been optimized. The CdZnTe detector performs good energy resolutions for ²⁴¹Am, ⁵⁷Co, and ¹³⁷Cs radiation sources, especially for ¹³⁷Cs (10.91 keV full width at half maximum [FWHM] at 662 keV). A linear relationship between the energy positions and spectrum channels indicates that the detector is effective for the precise energy detection from 59.5 to 662 keV. Finally, neutron and gamma events were detected simultaneously at room temperature using ²⁴¹AmBe neutron source. The spectrum shows good energy resolution for neutron capture gamma ray (14.28 keV FWHM at 558 keV). Our work demonstrates that the quasi-hemispherical CdZnTe detector is promising for simultaneous detection of neutrons and gamma radiation.     

Ion beam induced charge imaging of charge transport in CdTe and CdZnTe

Ion beam induced charge (IBIC) imaging is a powerful technique for quantitative mapping of the charge transport performance of wide bandgap semiconductor materials. In this paper we present results from a study of electron and hole mobility-lifetime product and drift mobility in CdTe:Cl and CdZnTe, which are semiconductor materials used for radiation detector applications. IBIC imaging has been used to produce mobility-lifetime product maps in CdTe:Cl and CdZnTe, revealing the influence of extended defects and tellurium inclusions and assessing the large area response uniformity of the materials. The recent extension of this method in the form of digital time-resolved IBIC is also discussed and time of flight maps are presented which give quantitative images of electron and hole drift mobility.     

Performance simulation and structure design of Binode CdZnTe gamma-ray detector

A new electrode structure CdZnTe （Cadmium Zinc Telluride） detector named Binode CdZnTe has been pro- posed in this paper. Together with the softwares of MAXWELL, GEANT4, and ROOT, the charge collec- tion process and its gamma spectrum of the detector have been simulated and the detector structure has been optimized. In order to improve its performance further, Compton scattering effect correction has been used. The simulation results demonstrate that with refined design and Compton scattering effect correction, Binode CdZnTe detectors is capable of achieving 3.92% FWHM at 122 keV, and 1.27% FWHM at 662 keV. Com- pared with other single-polarity （electron-only） detector configurations, Binode CdZnTe detector offers a cost effective and simple structure alternative with comparable energy resolution.     

Method for converting in-situ gamma ray spectra of a portable Ge detector to an incident photon flux energy distribution based on Monte Carlo simulation

A matrix stripping method for the conversion of in-situ gamma ray spectrum, obtained with portable Ge detector, to photon flux energy distribution is proposed. The detector response is fully described by its stripping matrix and full absorption efficiency curve. A charge collection efficiency function is introduced in the simulation to take into account the existence of a transition zone of increasing charge collection after the inactive Ge layer. Good agreement is obtained between simulated and experimental full absorption efficiencies. The characteristic stripping matrix is determined by Monte Carlo simulation for different incident photon energies using the Geant4 toolkit system. The photon flux energy distribution is deduced by stripping the measured spectrum of the partial absorption and cosmic ray events and then applying the full absorption efficiency curve. The stripping method is applied to a measured in-situ spectrum. The value of the absorbed dose rate in air deduced from the corresponding flux energy distribution agrees well with the value measured directly in-situ.     

蒙特卡罗方法在CZT探测器测量乏燃料组件燃耗中的应用

利用碲锌镉（CZT）探测器组成的γ谱探测系统是一种测量乏燃料组件燃耗的较有效的方法。本文利用蒙特卡罗方法,借助于Geant4软件包计算在两种测量方式、多个准直高度条件下组件中¹³⁷Cs和¹³⁴Cs的全能峰探测效率,对测量结果的正确评价分析具有一定意义。另外,采用偏倚抽样方法确定源粒子发射方向,极大提高了CZT探测器全能峰探测效率。     

Clustering Method to Process Signals from a CdZnTe Detector

The poor mobility of holes in a compound semiconductor detector results in the imperfect collection of the primary charge deposited in the detector. Furthermore the fluctuation of the charge loss efficiency due to the change in the hole collection path length seriously degrades the energy resolution of the detector. Since the charge collection efficiency varies with the signal waveform, we can expect the improvement of the energy resolution through a proper waveform signal processing method. We developed a new digital signal processing technique, a clustering method which derives typical patterns containing the information on the real situation inside a detector from measured signals. The obtained typical patterns for the detector are then used for the pattern matching method. Measured signals are classified through analyzing the practical waveform variation due to the charge trapping, the electric field and the crystal defect etc. Signals with similar shape are placed into the same cluster. For each cluster we calculate an average waveform as a reference pattern. Using these reference patterns obtained from all the clusters, we can classify other measured signal waveforms from the same detector. Then signals are independently processed according to the classified category and form corresponding spectra. Finally these spectra are merged into one spectrum by multiplying normalization coefficients. The effectiveness of this method was verified with a CdZnTe detector of 2 mm thick and a ¹³⁷Cs gamma-ray source. The obtained energy resolution was improved to about 8 keV (FWHM). Because the clustering method is only related to the measured waveforms, it can be applied to any type and size of detectors and compatible with any type of filtering methods.     

Spectroscopic response of coplanar diamond alpha particle detectors

The performance of a chemical-vapor deposited (CVD) diamond radiation detector with an interdigitated coplanar electrode geometry is reported. The coplanar structure produces a shallow lateral electric field distribution. Consequently, charge transport occurs in a region close to the growth surface of the CVD diamond film, where the drift lengths are maximized. The spectroscopic performance of the coplanar diamond detector was investigated using alpha particles from a ²⁴¹ Am source, and also using a scanning 2-MeV proton microprobe. A broad full energy peak was observed using 5.49-MeV alpha particles, with an overall charge-collection efficiency of approximately 16% at a bias voltage of 300 V. The performance of this device is discussed with reference to Monte Carlo simulations of charge transport in coplanar electrode geometries