Compton recoil electron tracking with silicon strip detectors

The application of silicon strip detectors to Compton gamma ray astronomy telescopes is described. The silicon Compton recoil telescope tracks Compton recoil electrons in silicon strip converters to provide an unique direction for Compton scattered gamma rays above 1 MeV. With strip detectors of modest positional and energy resolutions, of 1 mm FWHM and 3% at 662 keV, respectively, true imaging can be achieved to provide an order of magnitude improvement in sensitivity to 1.6×10 ^-6 γ/cm²-s at 2 MeV. The results of extensive Monte Carlo calculations of recoil electrons traversing multiple layers of 200 μm silicon wafers are presented. Multiple Coulomb scattering of the recoil electron in the silicon wafer of the Compton interaction and the next adjacent wafer is the basic limitation to determining the electron's initial direction     

Bonded wafer substrates for integrated detector arrays

Bonded wafer substrates that are optimized for integrating high-energy-particle silicon detector arrays with their readout electronics have been fabricated. The detectors are processed in the handle wafer, which is a 300-μm-thick, high-resistivity, <111> silicon wafer. This wafer is bonded to a primary wafer using a low-temperature process that does not affect the detector material. The support electronics are processed in the remnant of the primary wafer, which is a submicron-thick <100> silicon film formed by a bond-and-etchback procedure. These two materials are isolated from each other by a radiation-hardened dielectric film. The integration process is based on a low-temperature, radiation-hardened VLSI CMOS process that is also shown not to seriously affect the detector material     

Detection of Low Energy Heavy Particles with Silicon Barrier Detectors

The performance characteristics of silicon surface barrier detectors have been investigated for detecting H+, He+, N+, Ne+ and Ar+ in the energy interval 6-100 keV. For a cryogenically cooled, 50 mm2, 1325? depletion depth detector the resolution for protons was 1.65 keV (FWHM). The resolution decreased as the particle mass increased being 6.5 keV for 40 keV Ar+. All particles exhibit pulse height linearity throughout the energy range.     

Silicon Surface Barrier Detector

A method has been established for producing silicon surface barrier detectors having an energy resolution of 0.7% for 5.3 MeV α particles, and which are stable for long periods of time. The fabricated detector has been proved to possess a depletion layer as thick as 200 μ and a surface layer with energy loss less than 15 keV for 5.3 MeV α particles. The stability of the detector was also tested and it was found to be stable for at least 2–3 months.     

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.     

Phantom experiments on a PSAPD-based compact gamma camera with submillimeter spatial resolution for small animal SPECT

We demonstrate a position sensitive avalanche photodiode (PSAPD) based compact gamma camera for the application of small animal single photon emission computed tomography (SPECT). The silicon PSAPD with a two-dimensional resistive layer and four readout channels is implemented as a gamma ray detector to record the energy and position of radiation events from a radionuclide source. A 2 mm thick monolithic CsI:Tl scintillator is optically coupled to a PSAPD with a 8mm×8mm active area, providing submillimeter intrinsic spatial resolution, high energy resolution (16% full-width half maximum at 140 keV) and high gain. A mouse heart phantom filled with an aqueous solution of 370 MBq (99m)Tc-pertechnetate (140 keV) was imaged using the PSAPD detector module and a tungsten knife-edge pinhole collimator with a 0.5 mm diameter aperture. The PSAPD detector module was cooled with cold nitrogen gas to suppress dark current shot noise. For each projection image of the mouse heart phantom, a rotated diagonal readout algorithm was used to calculate the position of radiation events and correct for pincushion distortion. The reconstructed image of the mouse heart phantom demonstrated reproducible image quality with submillimeter spatial resolution (0.7 mm), showing the feasibility of using the compact PSAPD-based gamma camera for a small animal SPECT system.     

薄窗型多阳极气体探测器研究进展

薄窗型气体探测器是最近发展并用于低能量加速器质谱探测技术。该探测器的入射窗采用氮化硅膜,薄而均匀,分辨率高,目前已在低能量粒子探测技术中得到初步应用,显示出广泛的应用前景。本文主要从薄窗型气体探测器基本原理、薄氮化硅膜与Mylar膜的对比、不同质子数Z的低能量粒子脉冲高度对比、薄窗型气体探测器与硅探测器的对比,以及应用等方面进行阐述。     

Intrinsic Efficiency of Germanium ? A Basis for Calculating Expected Detector Efficiency

A method is presented whereby the intrinsic efficiency of Ge is utilized to calculate the expected peak efficiency of detectors having a wide range of sizes. The intrinsic efficiency of Ge, which is the probability for total absorption, was measured at 122 and 136 keV in Ge(Li) coaxial detectors and HPGe planar detectors having an effective thickness ranging from 5 to 50 mm. At 136 keV it is 64% for a thickness of 10 mm and 82% for 20 mm, after which it levels off reaching 89% at 50 mm. It is shown that the peak efficiency of a detector is a product of only the intrinsic efficiency and the solid angle, once losses due to edge escape and detector imperfections (surface channels and high dislocation densities) are determined. The absolute and relative [to NaI(T1)] peak efficiency of a sample detector, calculated on the basis of intrinsic efficiency, are in good agreement with measured values. This method should find applications in the design of new detector systems particularly those for diagnostic imaging with 99Tc (140 keV).     

用于~(16)C核集团结构实验研究的望远镜探测器阵列性能研究

对16C核集团结构实验研究中使用的望远镜探测器阵列的性能进行了研究,此望远镜阵列主要用于靶后反应产物的探测及粒子鉴别。探测器阵列由9组望远镜组成,其中包括了硅微条、位置灵敏硅探测器(PSD)、大面积硅探测器(SSD)和CsI探测器单元在内的多种类型的探测器。用241Amα源对组成望远镜的各探测器进行了测试和优化,且在中国科学院近代物理研究所的重离子加速器放射性次级束流线(RIBLL)上进行了在束测试。结果表明,研制的望远镜探测器阵列具有较好的能量分辨、高的角分辨及粒子鉴别能力,可满足通过碎裂反应来研究16C等原子核的集团结构的需要。     

一种可测低能γ和X射线的高纯n型硅探测器

采用蒸发金、钯和离子注入硼作势垒接触,低温扩散锂制备欧姆接触的方法,制成性能良好的低能γ和X射线高纯硅探测器。介绍其制作方法和性能。探测器有效面积为14.5mm~2,厚度3.3mm。在液氮温度下对~(55)Fe 5.9kev X射线的最佳能量分辨率为162eV,对~(241)Am59.5keV低能γ射线的最佳能量分辨率为373eV。同时对三种不同制作方法所得的高纯硅探测器和Si(Li)X射线探测器进行了对比。     

Detection of Mössbauer γ-rays from 73Ge and 181Ta

Lithium-drifted silicon and intrinsic germanium detectors are compared as detectors for the recoilless γ-rays from ⁷³Ge at 13.3 keV and from ¹⁸¹Ta at 6.2 keV. In both cases it is found that the ratio of recoilless gamma counts to noise counts is substantially better with the intrinsic germanium detector. As a result of this improved background rejection, large Mössbauer absorption effects are seen with both isotopes. It is believed that the possibilities discussed here for reducing detector background will be of value in many experiments involving low energy X- or γ-ray fluorescence.     

Silicon Detectors for Low Energy Particle Detection

Silicon detectors with very thin entrance contacts have been fabricated for use in the IMPACT SupraThermal Electron (STE) instrument on the STEREO mission and for the Solid State Telescopes on the THEMIS mission. The silicon diode detectors were fabricated using a 200 Aring thick phosphorous doped polysilicon layer that formed the thin entrance window. A 200 Aring thick aluminum layer was deposited on top of the polysilicon in order to reduce their response to stray light. Energy loss in the entrance contact was about 350 eV for electrons and about 2.3 keV for protons. The highest detector yield was obtained using a process in which the thick polysilicon gettering layer was removed by chemical etching rather than chemical mechanical polishing.     

基于GAGG:Ce晶体耦合SiPM的位置灵敏探测器的设计与评估

为满足当前γ相机对高分辨率、低成本、小型化探测器的需求,提出了采用硅光电倍增管（SiPM）耦合GAGG:Ce晶体阵列的方式代替传统的位置灵敏型光电倍增管（PSPMT）耦合晶体阵列的方式以构成新型γ相机探测器,并设计了均匀电荷分配电路（SCDC）和阻抗电桥电路作为探测器的读出电路,同时设计了前沿定时电路作为数据采集触发电路。实验结果表明：当温度为25 ℃、探测器供电电压为28.5 V时,该探测器在511 keV射线的激发下,散点图的峰谷比高达3.84,对511 keV和662 keV射线的平均能量分辨率分别为10.63%和9.71%,具有较好的分辨性能。     

Hybrid direct conversion detectors for digital mammography

Hybrid pixel detector arrays that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. This technology also has wide application possibilities in other fields of radiology and in industrial imaging for applications in nondestructive evaluation and inspection. These detectors have potentially superior properties compared to either emulsion based film, which has nonlinear response to X-rays, or phosphor-based detectors in which there is an intermediate step of X-ray to light photon conversion. Potential advantages of direct conversion detectors are high quantum efficiencies (QE) of 98% or higher (for 0.3 mm thick CdZnTe detector with 20 keV X-rays), improved contrast, high sensitivity and low intrinsic noise. These factors are expected to contribute to high detective quantum efficiency (DQE). The prototype hybrid pixel detector developed has 50×50 microns pixel size, and is designed to have linear response to X-rays, and can support a dynamic range of 14 bits. Modulation Transfer Function (MTF) is measured on a l-mm silicon detector system where 10% or better modulations are obtained at 10 lp/mm spatial frequency. Preliminary DQE measurements of the same system yields a value of 55% at zero spatial frequency. Here, the authors report data of their first full size prototype readout ASIC chips hybridized with both silicon and CdZnTe detector arrays and present initial MTF and DQE measurement results as well as some test images     

硅光电管-闪烁体探测器γ谱仪研制

实验研制了硅光电管-闪烁体探测器γ谱仪。该γ谱仪用硅光电倍增管代替普通光电倍增管作为闪烁体探测器的光学读出端,配置闪烁体探测器,构成新型γ谱仪。测试结果表明:新型γ谱仪随温度漂移变化程度大;能量线性较好,线性相关度R为0.9987;配置LaBr_3:10%Ce~(3+)晶体,其能量分辨率为4.3%~4.9%;配置NaI(TI)晶体,其能量分辨率为8.4%。     

基于GATE的双平板正电子发射乳腺断层成像系统的仿真研究

采用Monte Carlo法仿真软件GATE,构建专用于乳腺成像的双平板正电子发射断层成像系统PEM并研究其性能。参考NEMA NU 4–2008标准,并在试验中略作改动。研究了PEM(positron emission mammography)的灵敏度、散射分数、晶体散射、计数率、固有空间分辨率等参数。结果表明,在350–650 keV能窗、6 cm平板间距下,系统灵敏度达14.17%,固有空间分辨率约1.2 mm;乳腺仿体活度为29.6 MBq时,噪声等效计数率NECR为1.508×105/s,满足PEM系统所需。     

Capabilities of Mercuric Iodide as a Room Temperature X-Ray Detector

Measurement results obtained with HgI2 detectors at room temperature in the low energy x-ray region down to 2 keV are reported. The best resolution obtained is 548 e V for 5.9 keV x-rays, and the 2.01 keV phosphorous x-ray line has been resolved with a detector with an area of 14 mm2. The different noise sources of the detector-amplifier system are analysed and polarization effects in the detectors are discussed. The mercuric iodide crystals were grown from the vapour phase by gradient reversal techniques.     

Stopping power measurements of 20–180 keV 1H and 4He in indium phosphide using thick target backscattering

The stopping power of InP for 20–180 keV ¹H and ⁴He was determined by measuring the absolute backscattering yield of thick InP targets. Several nonideal aspects of surface barrier detectors were observed which should be accounted for when making low to medium energy backscattering yield measurements. These are: non-Gaussian detector resolution, nonlinear detector energy calibration, and ion reflection in the detector Au window. The present ¹H in InP stopping cross section measurements are in good agreement with those recently obtained by Khodyrev et al. using a relative, bulk yield, single spectrum approach. The ⁴He in InP stopping cross section measurements were found to be velocity proportional below 30 keV/amu. The estimated standard error of the measurements is ±7% at 20 keV and ± 4% at 180 keV.     

Resolution and sensitivity as a function of energy and incident geometry for germanium detectors

The use of modeling programs such as MCNP to predict the response of HPGe detectors is increasing in importance. Accurate simulation of germanium detectors to incident gamma rays relies on knowledge of the performance of the detector in different detector–source geometries. Two important performance parameters are the resolution and sensitivity. The resolution is the FWHM and FW.1M/FWHM ratio. The IEEE 325-1996 standard only specifies the FWHM measurement at one geometry and two energies. Nearly all measurements are made in a different geometry and at other energies. Other investigators [Specifications for Today’s Coaxial HPGe Detectors, 2001 ANS Annual Meeting, Milwaukee, WI; Metzger, private communication, see also: Radionuclide Depth Distribution by Collimated Spectroscopy, 2002 ANS Topical Meeting, Santa Fe, NM], have shown that the sensitivity and resolution change with position of the incident gamma ray on the front of the detector. Such variability has possible implications for the accuracy of peak shape and area determination, since the calibration is potentially a function of angle of incidence. To quantify the sensitivity and resolution variation as a function of energy and point of incidence, measurements have been made on several coaxial detectors of various crystal types and sizes in different source–detector geometries. The full-energy peaks from 59 keV to 2.6 MeV were used. The detectors were placed in a low-background shield to reduce any contribution from external sources. None of the detectors tested was a low-background type. The sources used were an ²⁴¹Am source, ⁶⁰Co source and a natural thorium oxide sample. The ²⁴¹Am 59 keV gamma rays were collimated by a 2 cm thick, 1 mm diameter lead collimator. Several gamma rays from the thorium source were used and collimated by a 10 cm thick and 2 mm diameter tungsten collimator. These collimated sources were used to collect spectra for the incident beam on the front and sides of the detectors. The peak widths were calculated using the methods outlined in IEEE 325-1996. Data are presented to show that the peak shape and sensitivity change with incident beam position and full peak energy.     

Fine Grained Silicon-Tungsten Calorimetry for a Linear Collider Detector

A fine grained silicon-tungsten calorimeter is ideal for use as the electromagnetic calorimeter in a linear collider detector optimized for particle-flow reconstruction. We are designing a calorimeter that is based on readout chips which are bump bonded to the silicon wafers that serve as the active medium in the calorimeter. By using integrated electronics we plan to demonstrate that fine granularity can be achieved at a reasonable price. Our design minimizes the gap between tungsten layers leading to a small MoliÈre radius, an important figure of merit for particle-flow detectors. Tests of the silicon detectors to be used in a test beam prototype as well as timing measurements based onsimilar silicon detectors are discussed.