CVD金刚石膜X射线探测器的研制及性能研究

金刚石以其独特的性能成为辐射探测器的理想材料.采用HFCVD方法制备了高质量、(100)取向的CVD金刚石膜,在此基础上研制出X射线探测器.使用55Fe 5.9keV X射线研究了CVD金刚石膜探测器的光电流和电荷收集效率.结果表明,探测器在偏压加到100V还具有好的欧姆接触;电场为50kV·cm-1时的暗电流与光电流分别为16.3和16.8nA;电荷收集效率η为45.1%,对应的电荷收集距离δ(CCD)为9.0μm.     

Investigation on the Priming effect of a CVD diamond microdosimeter

CVD Diamond microdosimeter is an ideal substitute of common Si,GaAs detector for extremely strong radiation experimental environment due to its high band gap energy,fast charge collection,low dielectric constant and hardness.In order to improve its character,a CVD diamond microdosimeter was irradiated by a proton dose of 46 Gy,and a lateral micro-ion beam induced charge (IBIC)technique was utilized to characterize it in low beam current(-fA),It was clearly shown that charge collection efficinecy and energy resolution were greatly improved after proton irradiation of that dose.Moreover,the homogeneities of both its counting performance and collection efficiency were enhanced.Proton irradiation of 46Gy has been proved to be an effective way to prime a CVD diamond.     

CVD金刚石微剂量仪的辐射优化研究

金刚石材料具有大的能带间隙、快的电荷收集和低的介电常数等，在较恶劣的实验环境下（如对于超大规模的强子对撞机和同步辐射加速器进行近距离、高辐射条件下的信号探测），有望成为常规的硅、砷化镓等探测器的替代品。为了改进金刚石探测器的性能，本文采用5MeV质子对CVD金刚石微剂量仪进行了辐照，并采用侧向微束离子诱导电荷（IBIC）技术分析研究其性能。实验发现：①经46Gy质子辐照后金刚石探测器的收集效率得到了很大的改善；②收集效率和计数的均匀性也得到了提高，尤其是计数的均匀性，在窄条宽很小情况下其均匀性已达95％以上。可见用质子辐照CVD金刚石是提高其性能的有效途径之一。     

CVD金刚石在辐射探测领域中的应用

随着低气压合成金刚石研究的深入,CVD金刚石质量及电学品质不断提高,高性能CVD金刚石电子器件的研制已成为该领域的热点研究课题之一。由于金刚石辐射探测器具有信噪比高、时间响应快、可以在极端恶劣环境中正常工作等优点,基于CVD金刚石的辐射探测器研制吸引了众多的研究兴趣。本文评述CVD金刚石辐射探测器的研究进展,对CVD金刚石辐射探测器研究中遇到的问题和发展前景作了分析和展望。     

使用Geant4模拟CAPture电极CdZnTe探测器对γ射线的响应

采用CAPture电极CdZnTe探测器获取X射线注量谱,为建立ISO 4037-1：1996标准以外的参考辐射和计算辐射场特殊剂量物理量的约定真值提供基础。CdZnTe探测器的主要缺点是由于空穴迁移率寿命积过小,导致电荷收集不完全,全能峰左侧出现低能尾。CAPture电极CdZnTe探测器采用扩展阴极降低阴极附近区域的电场强度,弱化空穴输运对电荷收集效率的影响,实现对低能尾的抑制。但由于探测器内的电场不再均匀,电荷收集效率无法用Hecht方程计算。本文根据Shockley-Ramo原理建立了CAPture电极CdZnTe探测器电荷收集效率计算公式,用有限元分析软件模拟了探测器内的电场分布。进而用Geant4软件开展了蒙特卡罗仿真计算,确定了载流子迁移率寿命积,并取得了与实测结果基本一致的脉冲幅度谱,为建立探测器的响应矩阵奠定了基础。     

Integrated front-end for a large strip detector with E, ΔEand position measurements

A large strip detector for position and energy measurement of heavy ions in a 100-MeV range has been realized. An improved version with an epitaxial thick layer for ΔE measurement is foreseen. This paper describes a charge preamplifier-shaper dedicated to an optimal use of the mentioned detector whose charge extracted will be positive. The dynamic range of 12 and 8 bit are expected for E and ΔE measurements, respectively     

Response Function and Sensitivity of Double-Diffused Silicon Detectors in High ?-Dose Rate Fields

Response Function and Sensitivity of Double-Diffused Silicon Detectors in High ?-Dose Rate Fields, R. W. Kuckuck, R. Bernescut, M. R. Zatzick and C. P. Jupiter - A number of double-diffused (PIN) silicon detectors were exposed to peak ?-dose rates of 1019 ?-MeV/cm2-sec generated by a flash x-ray machine. Detailed examination of the rate and linearity was accomplished by superposition of a 200 Mc Rossi signal on the oscilloscope traces of the test detector, as well as that of the non-saturable monitor detector. At detector bias voltages of 3000 V, and load impedances of 25 ohms, peak linear currents of approximately 48 amps were observed with rise times of less than 10 nanoseconds. Sensitivity measurements of the detectors were obtained at lower dose rates of about 1016 ?-MeV/cm2-sec by exposure to a thick target bremsstrahlung source, using a 10 MeV Linac beam. The current-time integral of a detector signal provided a measure of the charge per pulse and a thimble ionization chamber was used to measure the average dose per pulse. Sensitivities are provided in units of amp/cm2/?-MeV/cm2-sec per micron of depletion depth. Results also include sensitivity vs detector bias voltage curves and calculated time response curves for an assumed ?-function gamma excitation pulse.     

An intranuclear cascade model for inelastic scattering and breakup reactions involving deuterons and alpha particles

The intranuclear cascade model is extended to cluster-induced (deuteron and alpha particle) nuclear reactions involving inelastic scattering and breakup reactions. The proposed model explains the projectile breakup process by describing the projectile cluster as a superposition of several states. The incident cluster and the produced cluster are assumed to be collections of independent particles and may undergo nuclear interaction through nucleon–nucleon interaction with the target nucleus. Trajectory deflections for the projectile and ejecta are incorporated in the model to account for angular distributions. Calculations with the proposed model followed by the generalized evaporation model are performed for validation by comparing with experimental double-differential cross-section spectra produced by bombarding an ²⁷Al target separately with 80-MeV and 99.6-MeV deuterons and 140-MeV alpha particles. The calculation results show good agreement with experimental spectra.     

Proton microbeam investigations on electrical properties of natural and CVD diamond

A proton microbeam has been used to obtain charge collection efficiency maps on cross sections of natural IIa diamond and CVD diamond samples with a sandwich arrangement of electrodes. Particular attention has been dedicated to the dependence of the collection efficiency profiles on bias polarity. Collection efficiency maps may be easily transformed into collection length profiles, giving information about the distribution of mobility and lifetime of carriers and the profile of the electric field.

Maps of the proton-induced luminescence have also been obtained. The results confirm the columnar distribution of the charge collection length in CVD diamond, while in natural diamond the distribution is relatively homogeneous.     

Spatially resolved imaging of charge collection efficiency in polycrystalline CVD diamond by the use of ion beam induced current

Diamond based detectors have potential applications in high energy physics experiments. These detectors can be fabricated from synthetic Chemical Vapour Deposited (CVD) polycrystalline diamond films. Previously it has been shown by the Turin group and their coworkers in Zagreb that it is possible to investigate the electrical characteristics of high quality polycrystalline CVD diamond films by Ion Beam Induced Current (IBIC). The present work describes IBIC images obtained using 2 MeV He⁺ irradiation of 250 μm thick polycrystalline diamond films through a thin gold surface contact layer biased positively relative to the grounded rear surface of the film. In contrast to previous experiments the present spectra of collected charge display a clearly defined peak from the induced charge. Images obtained by separating these spectra into different regions of interest allow the identification of regions in the sample of different charge collection efficiency. In particular the presence of some grains in which no charge collection appears possible and the reduction in charge collection efficiency at the grain boundaries is evident.     

W/BDD薄膜电极制备及其电化学性能研究

利用化学气相沉积（CVD）法研制了一种钨基硼掺杂金刚石（W/BDD）薄膜电极,通过扫描电镜和Raman光谱考察了W/BDD薄膜电极的性能,通过电化学方法测定了其在LiCl-KCl熔盐中的电化学窗口和电化学性能。结果表明,研制的W/BDD薄膜电极的BDD薄膜有较好的微观结构;W/BDD薄膜电极在LiCl-KCl熔盐中的电化学窗口约为3.5 V(-2.5～1.0 V,相对于Ag/AgCl参比极电位);电解过程中,氧离子不与W/BDD薄膜电极表面BDD薄膜层的碳反应,直接被氧化为氧原子;长时间电解不会改变电极表面薄膜层的形貌和结构。     

Observation of Alpha Particle Effects in the Charge-Coupled Image Sensor

Alpha particle effects in the charge-coupled (CCD) image sensor were evaluated by using Am-241, Th, and Po-210 radiation sources. Soft error rate due to alpha particle hit was dependent upon alpha energy spectrum and on integration time and photogate bias of the device. The device was operated at frequencies between 200 kHz and 1 MHz during the irradiation and was found to have no effect on the soft error rate. A charge collection efficiency of 64% was observed as the device was exposed to a 4.2-MeV alpha. Material-asssociated characteristics such as diffusion length and lifetime of the minority carrier were calculated from the outcome of the charge collection efficiency. More than two orders of magnitude in increase of dark signal and charge transfer loss were observed as the device was subjected to a total radiation exposure of 105 rads (Si). The device degradation is due mainly to the threshold voltage shift and lattice defects.     

Satellite-based detection of 16.76 MeV γ-ray from H-bomb D-T fusion

Based on the high energy γ-ray yield from the H-bomb D-T fusion reaction,it brings forward the idea applying the 16.76 MeV γ-ray to judge whether the H-bomb happens or not,and to deduce the explosion TNT equivalent accurately.The Monte Carlo N-Particle was applied to simulate the high energy γ-ray radiation characteristics reaching the geosynchronous orbit satellite,and the CVD diamond detector suit for the requirements was researched.A series of experiments were carried out to testify the capabilities of the diamond detector.It provides a brand-new approach to satellite-based nuclear explosion detection.     

Satellite-based detection of 16.76 MeV γ-ray from H-bomb D-T fusion

Based on the high energy γ-ray yield from the H-bomb D-T fusion reaction, it brings forward the idea applying the 16.76 MeV γ-ray to judge whether the H-bomb happens or not, and to deduce the explosion TNT equivalent accurately. The Monte Carlo N-Particle was applied to simulate the high energy γ-ray radiation characteristics reaching the geosynchronous orbit satellite, and the CVD diamond detector suit for the requirements was researched. A series of experiments were carried out to testify the capabilities of the diamond detector. It provides a brand-new approach to satellite-based nuclear explosion detection.     

基于三维正交条形碲锌镉探测器的DOI-PET显像研究

为对511 keV伽马光子进行三维定位,提高PET显像性能,研制一种尺寸为16.4 mm×16.4 mm×5 mm正交条形碲锌镉（CZT）探测器,并测试其PET显像性能。在32个电极读出后均采用电荷灵敏前置放大器和滤波放大模块,输入高速模数转换器对数据进行采样,得到探测器中信号的全脉冲形状,并利用模拟数字转换器（ADC）内置可编程门列阵（FPGA）对信号进行在线处理,对信号完成寻峰、滤波等数字化处理。结果表明,该碲锌镉探测器对511 keV伽玛光子的能量分辨率为6.35%,通过对碲锌镉探测器的电极结构分析得出了一套伽马光子相互作用的三维位置坐标计算公式,可以达到亚毫米位置分辨率,实现了碲锌镉探测器三维显像功能。     

Charge collection efficiency mapping of interdigitated 4H–SiC detectors

The Ion Beam Induced Charge (IBIC) technique was used to map the charge collection efficiency (CCE) of a 4H–SiC photodetector with coplanar interdigitated Schottky barrier electrodes and a common ohmic contact on the back side.IBIC maps were obtained using focused proton beams with energies of 0.9 and 1.5 MeV, at different bias voltages and different sensitive electrode configurations (charge collection at the top Schottky or at the back Ohmic contact).These different experimental conditions have been modeled using a two-dimensional finite element code to solve the adjoint carrier continuity equations and the results obtained have been compared with experimental results. The excellent agreement between the simulated and experimental CCE maps allows an exhaustive interpretation of the charge collection mechanisms occurring in pixellated or strip detectors.     

Development of the high-energy neutron fluence rate standard field in Japan with a peak energy of 45 MeV using the 7Li(p,n)7Be reaction at TIARA

In this study, we developed a 45 MeV neutron fluence rate standard of Japan. Quasi-monoenergetic neutrons with a peak energy of 45 MeV in the neutron standard field were produced by the ⁷Li(p,n)⁷Be reaction using a 50-MeV proton beam from an azimuthally varying field (AVF) cyclotron of the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA). The neutron energy spectrum was measured using an organic liquid scintillation detector and a ⁶Li-glass scintillation detector by the time-of-flight method, and using a Bonner sphere spectrometer by the unfolding method. The absolute neutron fluence was determined using a proton recoil telescope (PRT) composed of the liquid scintillation detector and a Si(Li) detector that was newly developed in the present study. The detection efficiency of the PRT was obtained using the MCNPX code. The peak neutron production cross section for the ⁷Li(p,n)⁷Be reaction was also derived from the neutron fluence in order to confirm the neutron fluence of the TIARA high-energy neutron field. The peak neutron production cross section obtained in the present study was in good agreement with those of previous studies. The characteristics of the 45-MeV neutron field in TIARA were successfully evaluated in order to calibrate high-energy neutron detectors and high-energy neutron dosimeters.     

Gamma-ray imaging laboratory measurements using externallysegmented germanium detectors

Fully two-dimensional gamma-ray imaging with simultaneous high-resolution spectroscopy using an externally segmented germanium sensor has been demonstrated in the laboratory with a calibrated radioactive source. The system employs a single high-purity coaxial detector with its outer electrode segmented into five distinct charge collection regions and a lead coded aperture, with a uniformly redundant array (URA) pattern. A series of one-dimensional responses was collected around 511 keV while the system was rotated in steps through 180°. A nonnegative, linear least-squares algorithm was then employed to reconstruct a two-dimensional image. Corrections for multiple scattering in the detector, and the finite distance of source and detector are made in the reconstruction process     

A novel radiation imaging sensor based on self-activated pixels

A new position sensitive detector for charged particles and X-rays is proposed based on pixels containing MOS transistors as preamplifiers. The output of the preamplifiers is shorted to strip buses to obtain two-dimensional information with readout requirements similar to a strip detector. The total pixel capacitance is low enough (20-40 fF) to allow a large potential increase at the pixel that collected the charge. The nonlinearity introduced by the large voltage rise effectively switches on the transistors of this pixel and leaves all the other pixels of the same line at a low transconductance state, resulting in an excellent noise performance     

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.