大面积闪烁光纤阵列探测器的在束测试

利用70AMeV²⁶Mg初级束流及其产生的次级束流,在兰州重离子加速器放射性次级束流线（RIBLL）终端测试了大面积闪烁光纤阵列探测器(LASFA)探测单元的时间分辨和位置分辨能力。利用70AMeV²⁶Mg初级束流测试得到的时间分辨约为128ps,对应的位置分辨约为10mm;利用次级束流测试得到的时间分辨约为158ps,对应的位置分辨约为13mm,具有很好的时间分辨和空间角分辨能力。结合RIBLL的ΔESi探测器,给出了ΔE_Si-TOF二维谱,并将测试结果与RIBLL的粒子鉴别系统进行详细比较。结果表明,大面积闪烁光纤阵列作为轻带电粒子的飞行时间终止探测器,性能优于RIBLL上采用的时间拾取探测器,可更清楚地鉴别次级束流。     

Monte-Carlo simulation for determining SNR and DQE of linear array plastic scintillating fiber

1 Introduction Radiation imaging detector can be designed ineither one or two dimension. Each kind of them has itsown advantages and disadvantages. One of the advan-tages of linear array detectors is its less effects ofscattering and crosstalk between pixels. These twoeffects are very important to make an image with highor low quality. This is the main reason for choosinglinear array in our research. So these effects can be shown in contrast andspatial resolution, which are crucial…     

高分辨率X射线探测器读出电子学系统的研制及性能测试

本文针对光锥耦合X射线探测器低噪声的设计要求,研制了一套读出电子学系统,该系统包括模拟驱动电路、前端处理电路及基于现场可编程门阵列(FPGA)的数字信号处理电路。利用X射线成像平台,对研发的探测器进行了性能测试。探测器系统绝对增益为0.168 6DN/e-,线性工作范围为0~154μGy。制冷温度为-20℃时,暗电流噪声为0.037e-/(pixel·s),读出噪声为10.9e-。探测器的本征空间分辨率达16lp/mm。测试结果表明,研制的读出电子学系统能满足高分辨率X射线探测器对低噪声特性的需求。     

高分辨率CCD辐射探测器串扰校正

近年来出现的新型闪烁体与科学级CCD图像传感器耦合的高分辨辐射探测器,对提高Micro-CT等高分辨成像系统的空间分辨率、信噪比、图像质量等有重要意义,具有广泛的应用前景。但新型闪烁体如Gd₃Al₂Ga₃O₁₂等发光传输的各向同性特性,给μm尺寸的CCD像元带来了严重的串扰噪声,导致辐射探测器系统空间分辨率的实际值与理论值相差甚远。本文理论分析了高分辨率CCD辐射探测器串扰产生的物理机理,提出了利用蒙特卡罗EGSnrc仿真和Zemax光学仿真工具理论计算探测器系统像元间的串扰率函数（CTF）,再以CTF为卷积核,通过Lucy-Richardson反卷积运算对实际投影数据进行串扰校正,用双丝型像质计进行验证实验。实验结果表明,本方法可有效校正探测器串扰噪声,对改善探测器系统的调制传递函数和提高空间分辨率等有明显的效果。     

Monte-Carlo simulation to determine detector efficiency of plastic scintillating fiber

1 Introduction The plastic scintillating fiber (PSF) has many applications in different fields such as particle trackingin high-energy particle physics, calorimeters, etc., buusing PSF as an imaging detector is the main goal othis research. Therefore, we selected 10~400 keVmono-energy electromagnetic radiation that is used inmedical and non-medical imaging (e.g. non destructive testing). Some scintillation characteristics of plastic scintillating optic fiber have been discover…     

大面积光纤阵列探测器探测单元性能的进一步测试

对大面积光纤阵列探测器中的光纤阵列探测单元的性能进行检测。测试了不同形状、不同材料的光导以及光导包裹不同反光材料时光纤探测单元的传输效率及时间分辨和位置分辨。确定了大面积光纤探测器探测单元所使用光导的材料和形状，给出了光纤阵列探测器探测单元可达到的时间分辨。     

Study of PET Detector Performance with Varying SiPM Parameters and Readout Schemes

The spatial resolution performance characteristics of a monolithic crystal PET detector utilizing a sensor on the entrance surface (SES) design is reported. To facilitate this design, we propose to utilize a 2D silicon photomultiplier (SiPM) array device. Using a multi-step simulation process, we investigated the performance of a monolithic crystal PET detector with different data readout schemes and different SiPM parameters. The detector simulated was a 49.2mm by 49.2mm by 15mm LYSO crystal readout by a 12 by 12 array of 3.8mm by 3.8mm SiPM elements. A statistics based positioning (SBP) method was used for event positioning and depth of interaction (DOI) decoding. Although individual channel readout provided better spatial resolution, row-column summing is proposed to reduce the number of readout channels. The SiPM parameters investigated include photon detection efficiency (PDE) and gain variability between different channels; PDE and gain instability; and dark count noise. Of the variables investigated, the PDE shift of -3.2±0.7% and gain shift of -4±0.9% between detector testing and detector calibration had the most obvious impact on the detector performance, since it not only degraded the spatial resolution but also led to bias in positioning, especially at the edges of the crystal. The dark count noise also had an impact on the intrinsic spatial resolution. No data normalization is required for PDE variability of up to 12% FWHM and gain variability of up to 15% FWHM between SiPM channels. Based upon these results, a row-column summing readout scheme without data normalization will be used. Further, we plan to cool our detectors below room temperature to reduce dark count noise and to actively control the temperature of the SiPMs to reduce drifts in PDE and gain.     

基于电子束扫描阵列微焦点射线源的倒置结构Micro-CT成像研究

倒置几何结构CT成像系统理论上具有扫描视场大、图像信噪比好、锥束伪影小等优点,但其多焦点、稀疏角的扫描模式亦会带来投影数据截断、稀疏和局部数据冗余等问题。本文利用电子束扫描阵列微焦点射线源和高分辨率小面积探测器等构建了一种新型高分辨率、大视场的倒置几何结构Micro CT实验系统(IG Micro CT)。针对该系统多焦点、稀疏角扫描模式下的投影数据截断和稀疏等特点,提出一种图像先验约束的全变分正则化SART迭代CT图像重建算法。首先通过仿真实验对图像重建算法进行了验证,并对阵列微焦点数量、旋转扫描分度数量等扫描参数进行优化,最后在IG Micro CT实验系统上获得了高分辨的Micro CT测试图像。实验结果表明,本文提出的算法适用于IG Micro CT系统,解决了投影数据截断、稀疏采样和局部数据冗余带来的条状等伪影问题,并验证了IG Micro CT这种新型成像方式的可行性。     

评价衍射增强成像空间分辨率的方法

衍射增强成像是X射线成像领域的前沿科技。相比于传统的吸收成像,衍射增强成像能大幅提高图像的衬度,尤其是对于由C、H、O、N等低原子序数元素构成的物体,这一特性使得衍射增强成像在医学诊断方面具有突出的应用价值。目前还没有系统评价衍射增强成像空间分辨率的方法。本文通过构建成像系统的调制传递函数模型,推导出衍射增强成像的空间分辨率计算公式,从而对衍射增强实验平台的整体性能进行综合评价。调制传递函数综合考虑了摇摆曲线几何、CCD像素尺寸、闪烁体荧光弥散效应对系统空间分辨率的固有影响,并详细分析了系统调制传递函数各因素对空间分辨率的影响规律,为衍射增强实验平台的物理设计及设备选型提供理论依据。     

Imaging studies for evaluating impact of position sampling techniques in PET scanners

Previously we have evaluated two crystal calibration techniques that can be applied to pixelated detector designs to improve system spatial resolution without detector motion. The inter-crystal positioning technique utilizes sub-sampling in the crystal flood map to better sample the Compton scatter events in the detector. The Compton scatter rejection technique, on the other hand, rejects those events that are located further from individual crystal centers in the flood map. Here we performed imaging studies with a Mini Deluxe hot rod phantom and a hot sphere phantom (sphere diameters of 4.95 and 7.86-mm with 6:1 uptake relative to background) using the standard crystal calibration technique, as well as the inter-crystal and Compton rejection calibration techniques. Our results show improved separation of 1.6-mm diameter hot rods with the two new crystal calibration techniques that is consistent with improved spatial resolution. For the hot sphere phantom the contrast recovery is improved with both the inter-crystal and Compton rejection calibration techniques over the standard calibration technique. The only drawback of the inter-crystal calibration technique is the increase in the number of possible lines-of-response (LORs) (factor of 16) that may slow image reconstruction. With the Compton rejection calibration technique, loss of counts leads to increased noise in the images.     

Investigation of OPET Performance Using GATE, a Geant4-Based Simulation Software

A combined optical positron emission tomography (OPET) system is capable of both optical and PET imaging in the same setting, and it can provide information/interpretation not possible in single-mode imaging. The scintillator array here serves the dual function of coupling the optical signal from bioluminescence/fluorescence to the photodetector and also of channeling optical scintillations from the gamma rays. We report simulation results of the PET part of OPET using GATE, a Geant4 simulation package. The purpose of this investigation is the definition of the geometric parameters of the OPET tomograph. OPET is composed of six detector blocks arranged in a hexagonal ring-shaped pattern with an inner radius of 15.6 mm. Each detector consists of a two-dimensional array of 8 × 8 scintillator crystals each measuring 2 × 2 × 10 mm(3). Monte Carlo simulations were performed using the GATE software to measure absolute sensitivity, depth of interaction, and spatial resolution for two ring configurations, with and without gantry rotations, two crystal materials, and several crystal lengths. Images were reconstructed with filtered backprojection after angular interleaving and transverse one-dimensional interpolation of the sinogram. We report absolute sensitivities nearly seven times that of the prototype microPET at the center of field of view and 2.0 mm tangential and 2.3 mm radial resolutions with gantry rotations up to an 8.0 mm radial offset. These performance parameters indicate that the imaging spatial resolution and sensitivity of the OPET system will be suitable for high-resolution and high-sensitivity small-animal PET imaging.     

基于伴随粒子的快中子成像系统角分辨研究

不同于传统的快中子成像系统,采用伴随粒子成像技术无需机械准直即可消除大部分γ射线和散射中子的干扰,实现对厚重物体的高对比度成像。角分辨是影响系统成像质量的一项重要参数。通过理论分析,研究了入射离子的初始动量、靶点尺寸和探测器空间分辨等多个因素对系统角分辨的影响。利用基于GEANT4的模拟程序,计算了不同参数下被标记中子出射角分布的二维图像。分析及模拟结果表明,靶点直径和α探测器空间分辨率是影响角分辨的重要因素。为满足系统角分辨小于1°的设计目标,入射离子的初始动量变化范围应较小,靶点直径应小于1 mm,同时α探测器的空间分辨率应小于0.5 mm。     

基于阵列式吸收发光CT法的辐射场实时测量系统的研究

分析了已有的各种核辐射剂量场测量方法的基础上, 利用闪烁体吸收发光特点并结合计算机实时成像处理技术,提出了对剂量场分布进行实时成像测量的新方法——阵列式吸收发光ＣＴ 法。研制出闪烁光纤阵列构成的探测器及其伺服控制系统, 用高灵敏度的电荷耦合器件（ＣＣＤ）拾取探测器产生的微弱闪烁光信号,并采用定点采集的方法对视频信号进行数据的快速采集。在图像重建方法上, 提出了迭代滤波反投影重建方法和利用非完全投影进行数据修复,对获取的投影数据进行变换和处理,并通过选择滤波函数及其适当的参数, 可获得最佳滤波效果,以重建剂量场的二维场分布,从而建立了剂量场的实时、高精度的成像测量系统。     

High energy X-ray computed tomography for industrial applications

A high energy X-ray computed tomography (CT) system with an electron linear accelerator was developed to image cross-sections of large-scale and high-density materials. An electron linear accelerator is used as the X-ray source. The maximum X-ray energy is 12 MeV, and the average energy is around 4 MeV. The intensity of the X-ray fan beam passing through the test object is measured by a 15-channel detector array. CWO (CdWO₄) scintillators and photodiodes are used as the X-ray detectors. The crosstalk noise due to scattering of X-ray photons by adjacent detectors is reduced to less than 1.6% by installing tungsten shields between the scintillators. Extra channels are used to compensate for base line shift of the circuits. These techniques allowed attainment of a dynamic range of more than 85 dB and a noise level comparable to the signal amplitude of X-rays transmitted in a 420-mm thick iron block. A spatial resolution of 0.8 mm was confirmed with an iron test piece 200 mm in diameter     

Some emission characteristics of scintillating fibers for lowenergy X and γ-rays

The characteristics of plastic scintillating fibers (PSF) are measured for X and γ photons in the energy range 5 keV to 1.5 MeV. It is shown that a very thin (50 μm) slit can be recorded with an array of very thin fibers having 50 μm diameter so that the main interaction mechanism is photoelectric absorption, instead of Compton scattering for low energy X-rays. The optical light attenuation, global efficiency and energy resolution have been measured for a system composed of 1 mm diameter fibers and a photomultiplier. An X-ray beam position detector is realized, using an intensified camera, allowing a 4% precision on the position. The effect of bending the fiber is also evaluated     

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LaBr3(Ce)晶体耦合SiPM阵列的可变角分辨率伽玛相机的设计与研制

编码孔径成像技术由于探测效率高、信噪比高、角分辨率好、成像质量稳定可靠等优点而广泛应用于核安全、核设施的去污及退役的测量、核医学等领域。建立通过改变编码准直器和探测器之间距离进而实现可变角分辨的伽玛成像系统。整个成像系统主要由编码准直器、位置灵敏探测(position sensitive detector, PSD)、数据采集卡以及图像重建系统组成。该成像系统的编码准直器采用修正均匀冗余阵列(modified uniformly redundant array, MURA)编码方式,为了保障对较高能量射线的探测能力,编码准直器的材料采用含钨量90%的钨铜合金,PSD通过LaBr₃(Ce)晶体耦合SiPM阵列组成,重建算法采用的是直接互卷积算法,快速高效。测试结果显示,整个位置灵敏探测器的平均能量分辨率为4.96%(662 keV);该辐射成像系统可以准确地对Am-241、Cs-137、Co-60进行清晰成像,并通过改变编码准直器和探测器之间的距离成功分辨出两个Cs-137点源的位置。     

利用同步辐射扭摆器光源研究X射线同轴轮廓成像质量

利用北京同步辐射光源研究了准平行束X射线同轴轮廓成像中影响成像质量的若干因素。结果表明,同步辐射光束在垂直方向能获得更好的边缘增强效果。尺寸较大的样品能获得更高的衬度。随着样品到探测器距离的增大,衬度增大,但存在一个最佳距离。高分辨率的探测器可以获得较高的衬度和较好的边界锐度。     

PIXE and the nuclear microprobe: Tools for quantitative imaging of complex natural materials

The 40 year history of nuclear microscopy has seen sustained progress in the development of technology needed to improve PIXE analysis and trace element imaging performance. Focussing systems have been developed for improved spatial resolution, detector systems have evolved to collect more signal, full-spectral scanning data acquisition approaches have been devised. The complexity of PIXE spectra has driven the development of techniques for fitting numerous overlapping components in spectra for quantitative analysis, methods have been developed for specialized problems in geology, such as the analysis of fluid and melt inclusions in minerals, and techniques for the deconvolution of elemental components in full-spectral scanning data sets have been developed to produce accurate element images. The future of nuclear microscopy using PIXE is promising. Lens system approaches have evolved and point towards ‘full bore’ acceptance, optimal matching to accelerator emittance, high current density and sub-μm spatial resolution using many nA beam currents. Detector arrays and integrated data acquisition and scanning systems are emerging that can collect all events across a large solid-angle collection area and process these events for element image display in real-time. The combination of these advances provides a path to greatly enhanced sensitivity for PIXE analysis and imaging and a more productive user experience. The emergence of detector array approaches for scattered particles and reaction products, and the development of software tools for coupled PIXE-RBS data reduction, suggest a path towards complementary RBS and NRA tools. The stage is set for an exciting and productive future for PIXE imaging on the nuclear microprobe.     

基于硅光电倍增管对塑料闪烁光纤衰减长度及光产额的研究

作为外靶实验终端（ETF）飞行时间探测的关键探测器,起始时间探测器需满足承受高计数率、高时间分辨和位置分辨等需求。塑料闪烁光纤（PSF）作为起始时间探测器改进方案的一种考虑,其衰减长度、光产额等性能参数将直接影响探测器的实际性能。本工作基于硅光电倍增管(SiPM)和PSF搭建相应的测试平台,系统研究了SiPM SensL MicroFC-SMA-30035和PSF Kuraray SCSF-78J的实际性能。结果表明：所选型号的SiPM具有优秀的单光子分辨能力,在所选工作电压范围内具有高增益及良好的增益线性,且具有较好的线性响应;光子在光纤中的衰减由两种成分组成,芯层光的有效衰减长度为547.4 cm,包层光的有效衰减长度为15.5 cm,光纤有效光产额约为552光子/mm,实际光产额约为968光子/mm。测试结果表明,采用该PSF结合SiPM读出的方式满足新型起始时间探测器的要求。