碲锌镉探测器的数字核信号处理系统设计

设计了完整的碲锌镉(Cd Zn Te,CZT)探测器数字核信号处理系统,包含了低功耗偏压电源、低噪声电荷灵敏放大器、数字梯形多道脉冲幅度分析器及数字上升时间甄别器。在考虑探测器与后端数字多道优化匹配前提下设计了低噪声电荷灵敏放大器;数字多道脉冲幅度分析器(Digital Multi-Channel Pulse Height Analyzer,DMCA)通过高速模数转换器将模拟核信号离散化后,在现场可编程门阵列(Field Programmable Gate Array,FPGA)中实现数字核脉冲信号处理;FPGA芯片中以快慢双通道梯形成形器为核心,针对碲锌镉探测器空穴收集不完全的问题,设计了数字上升时间甄别模块,有效消除了空穴拖尾效应,显著提升碲锌镉探测器的能量分辨率。从实验结果可知,针对西北工业大学提供的4 mm×4 mm×2 mm的准半球结构碲锌镉探测器对241Am的分辨率最佳可达3.6%,对137Cs的分辨率可达0.96%。     

碲锌镉探测器对低能X射线的探测

介绍了碲锌镉探测器对低能X射线的探测,并在不同温度下测试了其性能变化,包括电子学噪声,能量分辨率和漏电流的变化.同时研制了低噪、性能稳定的厚膜电路用于单路信号的读出,对241Am的60keV能量峰的能量分辨率达到了4%.     

N型碲锌镉探测器的制备和性能

碲锌镉(CZT)晶体由于原子序数高、禁带宽、密度大,制成低能γ射线和X射线探测器不需液氮冷却就能得到相当好的能量分辨率,且有相当高的探测效率,因此近年来发展迅速。我们实验室已制成φ8mm×1.7mm灵敏体积的CZT探测器,室温22℃下对241Am放射源59.54keV能量的γ射线能量分辨率可以达到2.06keV(FWHM)(未使用准直器),连续测量没有极化效应,并且具有很好的长期稳定性。     

CZT探测器测量α谱模拟研究

利用MC法研究碲锌镉探测器测量α谱的可行性。模拟计算了碲锌镉灵敏体厚度和面积、电极材料和厚度以及真空度对探测效率的影响,选择探测器最佳设计方案。并搭建了一套基于碲锌镉探测器的α谱测量系统,实验结果与模拟结果吻合。     

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。     

像素CdZnTe探测器的研制

介绍了研究的像素CdZnTe探测器的研发情况,包括探测器的制作和性能检测.4×4面阵CdZnTe的尺寸为11 mm×11 mm×6.3 mm,像素为2 mm×2mm.性能最好的一个像素对137Cs 662keV伽玛射线的能量分辨率达到了1.4%,在加保护环并进行各像素峰位归一修正后,整个CdZnTe探测器对 137Cs 662keVγ射线的能量分辨率为2.08%.     

脑专用PET显像探测器自由结构符合与初步实验测试

采用脑PET进行人脑功能的研究对生物医学起到至关重要的作用,为了显著提高脑PET显像质量,增加探测效率、实时显示图像,本文设计一种脑专用PET显像大面积平板型探测系统,该探测系统由两个大面积探头组成,每个大面积探头包含3×3阵列的位置灵敏光电倍增管和多个紧密排布的硅酸钇镥闪烁晶体（Ce：LYSO)阵列。并利用1 μCi的²²Na点源对晶格大小为0.7 mm×0.7 mm等六种LYSO晶体阵列进行晶体性能测试,并选用两块晶格大小为1.5 mm×1.5 mm的LYSO晶体阵列进行一对一符合探测初步断层显像。结果显示,各种晶格大小的LYSO晶体阵列的位置区分轮廓的半高宽平均值在0.38~0.49 mm之间,平均能量分辨率（半高宽）在17.61%~30.40%之间;在对²²Na点源的初步图像断层扫描实验测试中,通过滤波反投影算法获得重建图像的空间分辨率为1.5 mm,验证了大面积平板型探测系统的可行性。     

电流型碲锌镉探测器伽马灵敏度性能优化

为验证亚禁带光照对电流型碲锌镉（CZT）探测器伽马灵敏度性能优化的可行性，利用钴源装置开展了亚禁带光照对CZT探测器伽马灵敏度影响规律研究。结果表明：在稳态γ射线辐照条件下，CZT探测器输出电流随时间的变化曲线（标定电流曲线）存在前沿过冲现象。这一现象主要与晶体内深能级陷阱对载流子的去俘获过程有关。利用亚禁带光照能调控晶体内深能级陷阱的占据份额，消除CZT探测器标定电流曲线的前沿过冲，实现探测器性能优化。当亚禁带光(850 nm)在CZT探测器中引入的光照电流为330 nA、工作电压为200 V时，CZT探测器对能量约125 MeV的γ射线的灵敏度为999×10-17 C·cm2，接近理论模拟给出的118×10-16 C·cm2。     

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。     

大面积高灵敏度编码相机探测器的设计与性能测试

编码孔径相机是一种定位放射性物质的设备,对丢失放射性物质的寻找以及监测具有重要的意义。为了满足编码孔径相机对核突发事故的污染区进行实时定位,并获得污染面积和污染程度等信息,采用大面积CsI(Tl)晶体阵列与光电倍增管(PhotoMultiplier Tube,PMT)阵列耦合的方式构建高灵敏度编码相机的探测器,以此提高探测效率并减少探测时间。该探测器由121根CsI(Tl)晶体构成11×11的阵列,每根晶体的尺寸为15 mm×15 mm×15 mm,通过光导与3×3的光电倍增管阵列耦合为一个探测器模块;由4个探测器模块组成2×2的阵列作为探头部件,采用自主设计的放大滤波成型以及单端转差分电路实现探测器信号的读出处理。通过测试发现,该探测器模块在662 keV的γ射线激发下,能很好地实现各个晶体条的位置分辨,且其平均能量分辨率为9.4%。测试结果表明:该探测器在位置分辨、能量分辨率、峰位一致性以及探测效率一致性等性能方面均能够满足高灵敏度编码相机成像的设计要求。     

用于卫星探测X、γ射线的大灵敏面积CdZnTe探测器的研发

CdZnTe(CZT)探测器不需要低温制冷就可在30～600keV较宽的能量范围内得到较好的空间和能量分辨,已成为研究宇宙空间X、γ射线场重要的探测器。本工作研究将4个甄别级10mm×10mm×5mmCZT平面探测器进行改制,并将其并联拼接成20mm×20mm×5mm较大面积的CZT探测器。经测试,大面积CZT探测器对¹²⁵I、²⁴¹Am、⁵⁷Co、¹³³Ba、¹³⁷Cs具有较好的能量线性响应,对¹³⁷Cs的662keVγ射线有较好的能量分辨。     

Characteristics of the new YAlO3:Ce compared with BGOand GSO

The characteristics of YAlO₃:Ce (YALO) used as a fast scintillation detector with high density (5.35 gm/cm³) and high light yield were investigated and compared with those of other scintillation materials. The decay of the scintillation light could be described by the sum of two exponentials with decay constants of 31 ns and 246 ns and contributing 98% and 2% to the total light yield, respectively. The light yield of 19700 photons/MeV was measured by comparing the number of photoelectrons produced in YAlO in BGO under the same conditions. The energy resolution at a gamma ray energy of 511 keV was 6.7% for a 4.0×8.0×25.0 mm³ sample. The FWHM of a timing measurement using two YAlO crystals detecting annihilation quanta (with 200 keV threshold) was 1.1 ns. Monte Carlo simulations showed that the crystal depth for the absorption of 90% of 511 keV gamma quanta is 51.8 mm in YAlO (compared with 25.2 mm in BGO)     

TOF-PET探测器定时性能初步研究

本工作采用LYSO晶体阵列和平板型位置灵敏光电倍增管H8500对TOF-PET探测器进行了初步设计,能分辨3.2mm×3.2mm的晶体阵列。与BaF₂探测器组成时间谱仪,测量正电子湮没射线的瞬发时间谱,得到379ps的符合时间分辨率。根据已测量的BaF₂探测器时间分辨率（159ps）,可计算得到所设计的TOF-PET探测器时间分辨率为344ps。预计与此相同的两个TOF-PET探测器对正电子湮没射线的符合时间分辨率可达486ps左右,为新型PET的研究提供了有利条件。     

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.     

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…     

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.     

康普顿成像系统角分辨影响因素的理论及模拟研究

为了对康普顿成像系统的结构设计提供参考,本文提出了一种理论与模拟计算相结合的对双层位置灵敏CZT晶体组成的康普顿成像系统散射角误差进行估算的方法,并利用该方法对康普顿成像系统散射角误差进行了研究。结果表明,对662 keV、1.33 MeV和2 MeV的入射光子,该成像系统的康普顿散射角误差分别为5.54°、4.82°和4.52°,散射角误差主要来自于探测系统位置分辨本领和能量分辨本领,探测材料多普勒效应引起的角误差相对较小。合理地限制康普顿散射角范围可有效改善成像系统角分辨能力,优化成像效果。     

High resolution X-ray photon-counting detector with scintillator-deposited charge-coupled device

We report on a new photon-counting detector possessing unprecedented spatial resolution and moderate spectral resolution for 0.1-100 keV X-rays. It consists of an X-ray charge-coupled device (CCD) and a scintillator. The scintillator is directly coupled to the back surface of the X-ray CCD. Low-energy X-rays below 10 keV can be directly detected by the CCD. The majority of hard X-rays above 10 keV pass through the CCD but can be absorbed by the scintillator, generating visible photons. We coupled needlelike CsI(Tl) on the front surface of the back-illuminated (BI) CCD. The high detection efficiency of BI CCDs in the visible band enables us to collect visible photons emitted from the CsI(Tl) efficiently, leading to the moderate spectral resolution of 28.4% at 22.1 keV and 25% at 59.5 keV. We also investigated the imaging capability of our device and demonstrated high resolution imaging with an accuracy of 10 /spl plusmn/3 /spl mu/m at 17.4 keV.     

NaI:TI与LaBr_3:Ce~(3+)闪烁体探测器能量分辨的GEANT4模拟

闪烁体探测器γ能谱测量中,闪烁光子的产生、传输及光电器件收集、倍增均对能谱的分辨有巨大影响。为了精确模拟闪烁体探测器的能量分辨,采用蒙特卡洛模拟软件GEANT4建立了一套模型,分别对Na I(TI),LaBr_3:0.5%Ce~(3+)闪烁体探测器测量能量为662 ke V的γ射线能谱进行模拟,获得的结果与实验测试结果能够很好的符合,验证了建立模型合理性与可靠性,为闪烁体的设计提供了一套更精确的开发工具。