γ相机准直器的质量指标对比研究

对比研究γ相机准直器的3个主要质量指标对评价和检测准直器质量的价值。用同型号低能通用低能高分辨平行孔准直器4只,参照NEMA标准（1994）,分别测试各准直器的系统均匀性,同时测试系统空间分辨率及灵敏度,对测试结果进行比较和分析。结果表明,同型号准直器的系统空间分辨率与灵敏度两项指标基本接近,而均匀性指标存在较大差异（当部分准直器存在质量问题时）。其中系统积分和微分均匀性分别超过6％和3％的3只准直器被证实存在质量问题。说明系统均匀性定量和定性地反映准直器的性能,是反映准直器质量问题的最基本和最有效指标。     

基于连续晶体的高性价比小型伽玛相机模块的设计

研究一种基于连续闪烁晶体配合位置灵敏光电倍增管(PSPMT)设计高分辨率小型伽玛相机模块的新方案。采用蒙特卡罗方法研究了压缩效应及内在空间分辨率与晶体参数的关系,进一步改进PSPMT的读出电路与定位方法,开发基于局域重心法的读出电子学电路,最后进行了成像实验测试。结果表明,基于局域重心法的读出电子学电路能够有效抑制晶体的压缩效应,晶体的空间分辨率和压缩效应都随着晶体厚度的减少而得到改善。因此,这种设计方案是可行的,其内在空间分辨率能够达到1?2mm,比采用晶体阵列有更好的性价比。     

用系统均匀性检测准直器质量

目的；用系统均匀性指标检测准直器的质量。材料和方法：同型号低能通用及同型号低能高分辨平行孔准直器各4只，用NEMA标准（1994）中固有泛源均匀性的方法分别测试带准直器的系统均匀性，同时测试系统空间分辨率及灵敏度，对测试结果进行比较和分析，结果：同一型号准直器的系统空间分辨率与灵敏度两项指标基本接近，而均匀性指标存在较大差异（当部分准直器存在质量问题时），其中系统积分和微分均匀性分别超过6%和3%的3只准直器被证实存在质量问题，结论：均匀性测试定量和定性地反映准直器的性能。能有效地反映准直器的质量问题。     

区域γ辐射定向监测仪准直器的设计

为区域γ辐射分布定向监测实验相机系统设计了一个针孔准直器。应用针孔准直器的解析公式,根据探测器内在分辨率和实验相机系统的预期分辨率,考虑探测器尺寸,确定了相机的焦距及准直器的张角;然后根据预期角分辨率计算有效孔径,得出孔径和孔深的范围;再利用蒙特卡罗方法模拟面源入射,在各种孔径和孔深组合中,挑选出透射和散射光子份额最小的组为最优组,对应孔径和孔深参数即为最优参数。     

NaI探测器搜寻γ源定位准直器模拟设计

为尽快搜寻丢失的γ放射源,模拟设计了用NaI探测器确定γ源方位的铅准直定位装置。设计针对铅准直NaI探测器,运用MCNP软件模拟定位γ源。模拟结果表明,设计的铅准直NaI探测器能够识别γ射线的方向,且角度分辨率高,放射源模拟定位的偏差小,在多个放射源形成的辐射场中能对各个放射源进行定位。     

强辐射环境下CMOS图像传感器噪声对相机分辨率的影响

CMOS图像传感器（CIS, CMOS image sensor）相机是照相装置中常用的成像设备。在核工业环境下的监控过程中,CIS易受γ辐射影响产生噪声,影响图像的成像分辨率,有必要从系统角度评估CIS相机抗辐照能力。通过利用60Co?γ放射源对CIS相机进行辐照实验,分别得到了典型CIS相机的噪声与图像分辨率和辐射剂量的函数关系,进而求出满足相应分辨率条件下CIS相机的辐照剂量上限。研究结果显示,对于相机成像图片目标区域的最小灰度值区域噪声数量占比σ≤2%,CIS相机电离总剂量（total ionizing dose, TID）小于150 krad（Si）,相机分辨率没有明显降低。并且在通过ISO 12233: 2014 eSFR测试相机分辨率中发现,利用基于楔形图获取混淆的开始频率测试法评估辐照相机分辨率参数比SFR测试法更具合理性。     

基于单管γ相机的SPECT系统的Monte Carlo研究

借助于Monte Carlo模似，仔细研究了基于单管γ相机的小型SPECT系统对特定活度分布的源响应特性。揭示了断层成像质量（空间分辨率、对比度）对系统准直器参数、角度采样频数的变化规律。     

γ相机空间分辨率测试

空间分辨率是γ相机的一项主要性能指标。在NEMA标准中,空间分辨率用线扩展函数峰值半高宽(FWHM)和十分之一高宽(FWTM)描述。测试FWHM和FWTM一般需要使用多道分析器,但在没有多道分析器的情况下,也可使用γ相机配置的电子计算机,按照NEME标准测试γ相机空间分辨率FWHM和FWTM。     

高分辨micro-SPECT成像系统针孔准直器的优化设计

为了最大限度地减少γ射线在针孔准直器上的透射和散射效应,采用蒙特卡罗方法对单光子发射计算机断层(SPECT)成像系统使用的针孔准直器进行优化.模拟计算结果与实验测试得到的系统灵敏度和空间分辨率曲线相符,达到了高分辨小动物成像的要求.     

半球型CdZnTe核辐射探测器的制备与性能

CdZnTe半导体核辐射探测器具有较高的探测效率和较好的能量分辨率,可方便地应用于X、γ射线的探测,在环境监测、工业无损检测等领域具有很好的应用前景.CdZnTe探测器有多种电极结构,其中半球型结构在国内鲜有研究.该工作制备了体积为8 mm×8 m×4mm的半球型CdZnTe探测器,经测试,在室温条件下,其漏电流为nA级,对未经准直的241Am(59.5 keV)、57Co(122 keV)、137Cs( 662keV)γ射线的分辨率(FWHM)分别为6.96％、5.66％、3.92％,在连续使用的条件下具有较好的稳定性.     

YAP multi-crystal gamma camera prototype

The Anger camera principle has shown a practical limit of a few millimeters spatial resolution. To overcome this limit, a new gamma camera prototype has been developed, based on a position-sensitive photomultiplier tube (PSPMT) coupled with a new scintillation crystal. The Hamamatsu R2486 PSPMT is a 76-mm diameter photomultiplier tube in which the electrons produced in the conventional bi-alkali photocathode are multiplied by proximity mesh dynodes and form a charge cloud around the original coordinates of the light photon striking the photocathode. A crossed wire anode array collects the charge and detects the original position. The intrinsic spatial resolution of PSPMT is better than 0.3 mm. The scintillation crystal consists of yttrium aluminum perovskit (YAP:Ce or YAlO₃:Ce). This crystal has a light efficiency of about 38% relative to NaI, no hygroscopicity and a good gamma radiation absorption. To match the characteristics of the PSPMT, a special crystal assembly was produced by the Preciosa Company, consisting of a bundle of YAP:Ce pillars where single crystals have 0.6×0.6 mm² cross section and 3 mm to 18 mm length. Preliminary results from such gamma camera prototypes show spatial resolution values ranging between 0.7 mm and 1 mm with an intrinsic detection efficiency of 37÷65% for 140 keV gamma energy     

Study of performance of small gamma camera consisting of crystal pixel array and position sensitive photomultiplier tube

1 Introduction In recent years a great effort has been made in developing compact gamma camera to improve nu-clear medical imaging. Conventional Anger gamma camera[1] uses a NaI(Tl) scintillator block and an array of photomultiplier tube. It has large size and poor spa-tial resolution, thus it is not suitable for small object image. Though the gamma camera using planar crystal coupled with position sensitive photomultiplier tube (PSPMT[2]) could greatly improve spatial resolu-tion,[3-5] pl…     

高分辨小型伽玛相机位置读出电路研究

本文介绍一种新型的位置读出方法,用于开发高分辨的小型伽玛相机.该伽玛相机采用小单元的CsI(Na)晶体阵列与位置灵敏光电倍增管(PSPMT)结合的探测器.其位置读出电路的设计把常规的阻抗电荷分配法与多路单通道直接读出法的优点结合在一起,由硬件实现局域重心法(Truncated center of gravity)计算读出的位置,取得很好的效果.该伽玛相机的内在分辨率接近1 mm,视野(FOV)达探测器的灵敏范围.这种新型的位置读出方法也可用于更高集成度的多阳极的位置灵敏光电倍增管的位置读出.     

Recent advances and future perspectives of position sensitive PMT

In recent years there has been a growing interest in developing compact gamma cameras to improve gamma ray imaging for application in nuclear medicine as well as in astrophysics, radiation physics and high energy physics. The gamma cameras based on position sensitive photomultipliers could be the best chance to obtain a realistic and low cost compact gamma camera.Since 1985 the development of position sensitive photo multiplier tubes (PSPMT) has shown the highest rate in technological advancement achieving very compact size (25 × 25 × 20 mm³) by a novel charge multiplication system. The PSPMT shows the same advantages of a standard gamma camera with the additional possibility to utilize scintillation arrays with pixel dimension less than 1 mm, thus achieving sub-millimeter spatial resolution values.The last technological advance is a PSPMT with Flat Panel structure, named H8500. Its dimension is 50 × 50 mm² with a narrow peripheral dead zone to place closely different modules achieving large detection areas. In this paper the technological development of different PSPMT generations is reviewed and some measurements of the first Flat Panel PMT prototype are presented and compared with ones from previous generation. Flat Panel PMT could be the best trade-off between compactness, large detection areas, effective area (packing density) and imaging performance.     

Development of a low-energy high resolution X-ray camera for high-energy gamma photon background environments

Although a high-energy gamma camera can obtain images of ¹³⁷Cs distribution by detecting the 662-keV gamma photons, its spatial resolution is reduced because high-energy gamma photons penetrate the edge of the pinhole collimator. To solve this problem, we developed a low-energy X-ray camera that detects the characteristic X-ray photons (32–37 keV) that are emitted from ¹³⁷Cs to obtain high resolution images. We used a 45 × 45 × 1-mm-thick NaI(Tl) scintillator that was encapsulated in 0.1-mm-thick aluminum and optically coupled to a 2-inch square, position sensitive photomultiplier tube (Hamamatsu Photonics, PSPMT:H12700 MOD) as an imaging detector. The imaging detector was encased in a 2-cm-thick tungsten alloy container and a pinhole collimator was attached to its camera head. The spatial resolution and sensitivity were ～5 mm full-width at half-maximum and ～0.6 cps/MBq for the 1.5-mm pinhole collimator 10 cm from the collimator surface, respectively. We administered 5 MBq of ¹³⁷Cs to a soybean seedling, imaged the distribution of radionuclides for six hours, and successfully obtained a high resolution image of it with our developed X-ray camera. We believe our camera will be a powerful tool for such ¹³⁷Cs imaging in plants.     

PSPMT基本特性的实验研究

介绍了ＰＳＰＭＴ的特性测试方法及得到的结果：⑴位置线性：绝对线性０．６３ｍｍ，微分线性０．１ｍｍ；⑵增益均匀性：≤３０％（在灵敏区内）；⑶空间分辨：０．４ｍｍ。     

Development of a compact high resolution gamma-ray detector for E-CT applications

A compact gamma-ray detector with good spatial resolution for emission computed tomography (E-CT) applications has been developed. The detector is composed of NaI(Tl) scintillation pixels array and Hamamastu R2486-05 PSPMT. Having a pixel size of 2 mm × 2 mm and an overall dimension of 48.2 mm × 48.2mm × 5 mm, it has 484 pixels in a 22×22 matrix. An average spatial resolution of 2.5mm (FWHM) was achieved. The slope of position linearity is constant within 10% in a range of 40mm. After corrections, the average value of differential non-linearity and absolute non-linearity were 0.16mm and 0.535mm respectively, and a 17% at FWHM of total energy resolution for 241Am was obtained.     

关联α粒子探测器设计和性能研究

关联粒子成像技术（API）是进行爆炸物检测和有源核查的重要手段,而关联α粒子探测器的空间分辨和时间分辨直接决定成像系统的空间分辨能力。本文依托中国原子能科学研究院核数据重点实验室移动中子发生器,结合具有快时间响应的ZnO：Ga与最新的位置灵敏光电倍增管(PSPMT)H13700,设计可用于API的关联α粒子探测器系统。通过SCDC-TCOG将256路信号简化为4路信号,利用数字化仪对信号进行采集分析。通过离线实验对关联粒子探测器的时间性能和空间分辨性能进行了测试。利用刀口法测得空间分辨好于1 mm,并通过狭缝法和栅条法进行了验证。通过测量²⁵²Cf裂变碎片和瞬发伽马符合测量获得系统时间分辨好于1 ns,达到了应用需求。     

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。