CsI∶Tl晶体对高能X光照射量的响应关系研究

在X光探伤系统中使用效率较高的CsI∶Tl晶体作为X光转换体。CsI∶Tl晶体对X光的响应关系是精密图像处理、定量测量所需的一项重要参量,理论上已经推导了CsI∶Tl晶体对X光的响应呈现线性关系,并针对性地设计了在60Co放射源上的定量测量实验,所获数据不仅充分证明了理论推导的正确性,还证明了相应系统的这种线性关系的线性度非常好。     

散射环境下钨的质量吸收系数测量

CsI：T1晶体在辐射成像系统中的作用是非常重要的，利用CCD作为图像记录的X光探测系统的响应性能与其有密切的关系。为了得到响应关系的大致形式，在30MeV的射频加速器上，曾经用厚度为5，10，20mm的CsI：T1晶体作过研究，对于每一种厚度的CsI：T1晶体，响应还是线性的，但是彼此之间响应度的相对关系还是存在较大差异；由于^60Co放射源的特点，又专门设计了用^60Co放射源作为高能γ光子源来对系统的响应特性作定量研究，并且得到了在几乎没有散射影响下的响应关系，实验结果严格符合理论推导结论，     

光学材料 光学晶体、液晶

O722006010691CsI∶Tl晶体对高能X光照射量的响应关系研究=Studyon the response characteristic of CsI∶Tl crystal to high-energy X-ray radiation[刊,中]/江孝国(中物院流体物理所.四川,绵阳(621900)),王伟…∥光学学报.—2005,25(10).—1429-1432在X光探伤系统中使用效率较高的CsI∶Tl晶体作为X光转换体。CsI∶Tl晶体对X光的响应关系是精密图像处理、定量测量所需的一项重要参量,理论推导出CsI∶Tl晶体对X光的响应呈现线性关系,并针对性地设计了在60Co放射源上的定量测量实验,所获数据不仅充分证明了理论推导的正确性,还证…     

CsI:Tl晶体对高能X光照射量的响应关系研究

在X光探伤系统中使用效率较高的CsI：Tl晶体作为X光转换体。CsI：Tl晶体对X光的响应关系是精密图像处理、定量测量所需的一项重要参量。理论上已经推导了CsI：Tl晶体对X光的响应呈现线性关系,并针对性地设计了在^60Co放射源上的定量测量实验,所获数据不仅充分证明了理论推导的正确性,还证明了相应系统的这种线性关系的线性度非常好。     

X光作用下CsI:Tl晶体的转换效率研究

X光转换材料在数字辐射成像系统中具有很重要的作用，它的效率对整个系统的量子探测效率起到决定性的作用。对CsI∶Tl晶体在X光激发下的发光效率进行详细分析，根据X光在物质中的衰减和吸收规律，从理论上推导了其对X光转换效率的关系，并建立了利用CCD相机作接收系统时的图像数据的表达形式，表明该系统输出与入射X光照射量成线性关系；并在30 MeV射频加速器上进行了实验验证。     

CsI（T1）晶体量能器中硅光二极管的核计数器效应研究

研究了由于电磁簇射在CsI（T1）晶体后端的泄漏而引起的硅光二极管“核计数器”效应．通过GEANT模拟和实验测量分析其在BESⅢ的CsI（T1）晶体量能器中对能量测量的影响．     

CsI光阴极在10-100 keV X射线能区的响应灵敏度计算

为了满足10-100 keV高能X射线光电探测器研究的需要,对CsI光阴极在该能量范围的响应灵敏度进行了研究.基于高能量X射线光子与材料相互作用的物理过程,分析了康普顿散射等效应对CsI响应灵敏度的影响.推导了CsI的响应灵敏度与二次电子平均逃逸深度和光阴极厚度的关系式和二次电子平均逃逸深度与入射光子能量的关系式,计算了CsI在10-100 keV范围内的响应灵敏度,计算结果与实验测试数据相符,验证了分析与推导的可靠性.根据计算可以获得不同入射X射线能量下CsI光阴极的最佳厚度,从而为高能X射线光电探测器的设计优化提供了理论参考.     

暗物质寻找实验中CsI（T1）晶体反符合探测器实验研究

一个正在建设的位于韩国Y2L地下实验室的低能暗物质探测实验中,采用了CsI（T1）晶体反符合探测器作为主动屏蔽体.本工作对CsI（T1）晶体反符合探测器的实验性能进行了研究.通过FADC系统记录的脉冲波形数据,研究了探测器的能量分辨率和波形甄别的能力;研究相同能量γ射线入射到反符合探测器不同位置的相对光输出将有助于选择探测器的工作参数;为了解晶体自身放射性对暗物质测量的影响,利用低本底HPGe探测器对CsI（T1）晶体内部的放射性进行了测量,得到晶体内部Cs同位素的放射性活度.探测器系统进行了约18d的试运行取数.实验数据表明,CsI（T1）晶体探测器的反符合效率约为31%,HPGe探测器的本底计数率水平约为133cpd.为了进行暗物质探测研究,需要采取有效的方法进一步降低探测器的本底水平.     

HIRFL-CSR ETF多层CsI(Tl)望远镜探测器能量刻度方法

在兰州重离子加速器冷却储存环（HIRFL-CSR）的外靶终端（ETF）,设计建造了一套多层CsI（Tl）望远镜探测器,用于对轻质量带电粒子的鉴别。这套探测器由7层CsI（Tl）晶体组成,每一层晶体光输出信号由4个光电倍增管分别在晶体4角读出。由于CsI（Tl）晶体对于重离子的响应是非线性的,且与入射离子的种类有关,这些因素使得对这台探测器的能量刻度需要做专门的研究。利用RIBLL2提供的能量在200 s~300 MeV/u的次级束流对探测器进行了测试,并针对第一片CsI（Tl）晶体的光输出以及所有CsI（Tl）晶体光输出的和的刻度方法分别进行了探索。在此能区下,第一片CsI（Tl）晶体猝灭现象可以近似忽略,即光输出与能量沉积近似呈线性。对于所有晶体光输出的和,利用一个经验公式对其进行刻度,利用这种刻度方法计算得到的光输出的值与实验测量值之间的差别小于5%。A multi-layer CsI(Tl) telescope has been designed and constructed at External Target in Facility (ETF) terminal of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou(HIRFL-CSR), and is used for identifying light charged particles. The detector consists of seven layers of CsI(Tl) crystals, and the signals of each crystal are read out by four photomultipliers at the corners. Since the response of the CsI(Tl) crystal to the heavy ions is non-linear and also depends on the species of the incident ions, the energy calibration method of the telescope must be carefully studied. With the help of the secondary beams selected by RIBLL2 in the energy ranges from 200 to 300 MeV/u, the telescope has been tested and the energy calibration method for the first-layer crystal together with the whole telescope has been investigated. In this energy region, the quench effect in the first-layer crystal can be neglected and a linear expression can be used to represent the relation between the light output and the energy deposition in the crystal. To the total light output of the telescope, an empirical formula is used for the energy calibration. The difference between the calculated results and the experiment data is globally less than 5%.     

CsI(Tl)晶体量能器中硅光二极管的核计数器效应研究

研究了由于电磁簇射在CsI(Tl)晶体后端的泄漏而引起的硅光二极管“核计数器”效应. 通过GEANT模拟和实验测量分析其在BESⅢ的CsI(Tl)晶体量能器中对能量测量的影响.     

狭长CsI(Tl)闪烁体发光效率的研究

提出了基于狭长CsI（Tl）闪烁体和面阵CCD器件，采用光纤和光纤面板进行光耦合及传输，以扇形束线阵扫描方式实现对X射线探测与成像的工业X-CT系统探测器方案.基此，通过物理分析及数学建模，利用Matlab模拟研究了X光能量小于450 keV时狭长CsI（Tl）闪烁体的发光效率等性能指标.研究结果表明：当光电吸收截面μph和康普顿吸收截面μc分别为0.000313和0.0000295、反射层反射系数R和衬底反射系数Rs分别取0.95和0.8、荧光线性吸收系数σ取0.000222 μm－1时，得到狭长CsI(Tl)闪烁晶体的长度l、高度h和宽度w取值范围分别是926～4512 μm、242～5000 μm和242～5000 μm的结论.在此范围内，既可使闪烁晶体有较好的空间分辨率又可获得最高的发光效率.     

Nd:GGG晶体荧光寿命的测试及受激发射截面的计算

介绍了荧光寿命的测试原理.设计了荧光寿命测试系统.利用脉冲取样技术测试了Nd:GGG晶体的荧光寿命,约为250μs.采用英国的荧光光谱仪,在室温条件下,用波长为488nm的Ar离子激光器激发Nd:GGG晶体,获得了Nd:GGG晶体的荧光光谱,计算出的Nd:GGG晶体的受激发射截面σ(λ)为21.57×10-20cm2.     

Temperature Effects of CsI(Tl) Crystal Detector with APD Readout

The temperature dependences of the light output of CsI(Tl) crystal grown at IMP and of the gain of the Hamamatsu S8664-1010 avalanche photodiode (APD) have been investigated systematically. The light output of the CsI(Tl) crystal increases with temperature by 0.67%/℃ in the region from －2℃ to 8℃, and by 0.33%/℃ in the region from 8℃ to 25℃, while the gain of the tested APD decreases by －3.68%/℃ (working voltage 400V) on average in the room temperature range. The best energy resolution 5.1% of the CsI(Tl) with APD was obtained for the 662keV γ ray from ¹³⁷Cs radiation source.     

Simulation of 12C+12C elastic scattering at high energy by using the Monte Carlo method

The Monte Carlo method is used to simulate the ¹²C+¹²C reaction process. Taking into account the size of the incident ¹²C beam spot and the thickness of the ¹²C target, the distributions of scattered ¹²C on the MWPC and the CsI detectors at a detective distance have been simulated. In order to separate elastic scattering from the inelastic scattering with 4.4 MeV excited energy, we set several variables: the kinetic energy of incident ¹²C, the thickness of the ¹²C target, the ratio of the excited state, the wire spacing of the MWPC, the energy resolution of the CsI detector and the time resolution of the plastic scintillator. From the simulation results, the preliminary establishment of the experiment system can be determined to be that the beam size of the incident ¹²C is φ 5 mm, the incident kinetic energy is 200-400 A MeV, the target thickness is 2 mm, the ratio of the excited state is 20%, the ight distance of scattered ¹²C is 3 m, the energy resolution of the CsI detectors is 1%, the time resolution of the plastic scintillator is 0.5%, and the size of the CsI detectors is 7 cm×7 cm, and we need at least 16 CsI detectors to cover a 0° to 5° angular distribution.     

X光高分辨探测用CsI(Tl)晶体的蒙特卡罗模拟研究

提出了一种基于CsI(Tl)闪烁晶体和面阵CCD器件、采用光纤和光纤面板进行光耦合及传输、以扇形束线阵扫描方式实现对X光高分辨探测的方案。CsI(Tl)晶体的尺寸大小将直接影响到晶体的发光效率及X光的高分辨探测,据此开展了蒙特卡罗模拟研究。模拟研究了X射线能量、X射线源到探测晶体的距离(源距)、CsI(Tl)晶体的厚度与X射线能量分布、全能峰效率与CsI(Tl)闪烁晶体转换效率之间的关系。结果表明,当X射线能量为120~450 keV,CsI(Tl)晶体尺寸厚度为0~1.5 cm变化时,全能峰效率的变化范围为31.34~96.74%,CsI(Tl)闪烁晶体的转换效率的变化范围为12.8~97.43%。可见,X射线的能量及CsI(Tl)闪烁晶体尺寸的厚度,是决定X光高分辨探测的重要参量,这对优化X光高分辨探测用CsI(Tl)晶体的尺寸设计具有一定的参考价值。     

Experimental Study on Image Shrinkage in a Planar Crystal γ Camera

The effect of the crystal's type and treatment on the performance of gamma camera consisting of planar crystal and position sensitive photomulitiplier tube (PSPMT) is studied via experiment. The results demonstrate that: (1) treatment of the edge surface of the crystal is very sensitive to the shrinkage of image, and the side-absorptionsurface is the best choice; (2) the intrinsic spatial resolution of the CsI (T1) crystal camera is worse due to its low light yield: in the center part it is - 1cm (FWHM) for 2mm aperture collirnated 241Am source; while using NaI(T1) crystal, it is -4mm.     

Monitoring the energy variation of an electron linac using a Cerenkov detector

A new method to monitor the energy variation of a multi-energy electron linac by combining a Cerenkov detector and a CsI(Tl) detector is reported. The signals in the Cerenkov detector show an appreciable but different dependence on the energy of the electron linac from the traditional CsI(T1) detector due to the particular response of the former to charged electrons with high velocity above threshold. The method is more convenient than the HVL (half-value layer) method which is commonly employed to calibrate the energy of an electron linac for real time monitoring. The preliminary validity of the method is verified in a dual-energy electron linac with 6 MeV and 3 MeV gears. Moreover, the method combining the Cerenkov detector and the CsI(Tl) detector is applicable to probe the X-ray spectrum hardened by the inspected material and may serve as a novel tool for material discrimination with effective atomic number in radiation imaging.