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.     

暗物质寻找实验中CsI(Tl)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(Tl)晶体反符合探测器作为主动屏蔽体. 本工作对CsI(Tl)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(Tl)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(Tl)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.     

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。     

Property measurement of the CsI (Tl) crystal prepared at IMP

Large-sized CsI(T1) single crystals,～Φ100 mmx350 mm,have been grown successfully,and this CsI(Tl) coupled with PD has been successfully utilized at RIBLL (the Radioactive Ion Beam Line in Lanzhou)to measure the energy of heavy ions as a stopping detector.The performances of CsI(Tl) detector coupled with PD and APD have been tested and compared,including the temperature dependence of scintillating light yield.     

CsI(Tl)晶体中反冲Cs和I核Quenching?Factor的测量

许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的.     

用于暗物质探测实验的CsI(Tl)晶体探测器性能的实验研究

在直接测量暗物质的实验中,反冲核能量的Quenching Factor是一个重要参数.用低能X射线源对一套测量入射中子引起的反冲核能量Quenching Factor的系统进行了能量刻度,得到了这套系统的能量响应关系.PMT单光电子的发射对应于晶体中的能量沉积约为0.32keV.同时研究了不同能量的X射线引起的PMT输出电流信号的积分时间宽度与积分电荷的关系,得到最佳的PMT输出电荷收集条件.     

CsI（Tl）+Si-APD探测器的性能测试

介绍了Si-APD的工作原理并对Si-APD中的暗电流进行了理论分析。基于RIBLL上产生的放射性核束流,使用CsI（Tl）+Si-APD探测器对中能重离子进行了能量测试。测试结果显示,CsI（Tl）+Si-APD探测器测量20 MeV/u的重离子时,可得到3%的能量分辨;同时还发现Si-APD中的暗电流大小以及入射粒子的能量大小都会对探测器的能量分辨产生影响。In this paper, the working principle of Si-APD was introduced and the dark current of Si-APD was analyzed theoretically. The intermediate energy heavy ions, which are produced on the RIBLL(Radioactive Ion Beam Line in Lanzhou), were measured with CsI(Tl)+Si-APD detector. The energy resolution of CsI(Tl)+Si-APD detector is about 3% for heavy ions with energy around 20 MeV/u. It is also found that the energy resolution of detector can be in uenced by the dark current of Si-APD and the energy of incident particles.     

A CsI(Tl) detector array used in the experiment of the proton-rich nucleus 17Ne

To investigate the configurations of the valence protons in Borromean nucleus 17Ne, a CsI(Tl) detector array, which consists of 9 CsI crystals (26×26×20mm3) coupled with photodiodes, has been successfully used in the 17Ne experiment to measure the energy of protons. In order to find the optimal working conditions and get the best energy resolutions, several technologies (including various wrapping materials, wrapping and coupling methods) have been used. The testing results showed that the best energy resolution of the CsI(Tl) is about 3.3% using the 241 Am α-source. The primary testing results with the proton beam were also provided.     

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%.     

基于GEANT4的CsI(Tl)闪烁体探测器的Monte Carlo模拟

对闪烁光在晶体内的传输以及光电子倍增过程进行了建模,基于GEANT4软件包对CsI(T1)闪烁体探测器进行了蒙特卡罗模拟, 得到了不同形状、尺寸和包装的CsI(Tl)晶体测量γ射线的能谱。对比模拟和测试结果,两者得到了很好的符合,从而验证了模拟参数的合理性和可靠性。该模拟程序的建立为闪烁体探测器的设计提供了更精确的开发工具。 With the modeling of the light transportation in crystal and electron multiplication in the PMT, a Monte Carlo simulation of CsI(Tl) scintillator detector has been implemented with Geant4 toolkit. The energy spectra simulated with different crystal shape, size and wrappings are obtained. And the reliability of the simulation parameters is confirmed by comparing with the measurements. The simulation code can be used as an reliable tool for the design of scintillator detectors.     

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.     

Size-induced effect on cathode luminescence spectra of CsI(Na) and CsI(Tl) crystals

We investigated the cathode luminescence characteristics of CsI(Na)and CsI(Tl)crystals by the spectrum and structure properties at room temperature.We fabricated three different sizes of CsI(Na)and CsI(Tl)crystals and measured their luminescence spectra under cathode rays.We found that CsI(Na)cathode luminescence peaks appear at 420 and 305 nm,and CsI(Tl)cathode luminescence peaks are 540 and 410 nm,the grain size affects CsI(Na)luminescence significantly,and the Na-related420 nm luminescence intensified relatively when the average grain size reaches~20μm,which becomes weak when the grain size is down to nano-scale.But the cathode luminescence spectra of CsI(Tl)crystals with different size have no obvious changes.Our explanations for these phenomena are that the different impurities in the same host material CsI lead to different luminescence mechanisms.These cathode luminescence characteristics indicate the suitability of CsI(Na)and CsI(Tl)crystals to match photomultiplier tube for large area crystal detector development.     

CsI(Tl)闪烁体软X光能量响应的模拟研究

CsI(Tl)闪烁体是X光转换为可见光比较重要的一个部件,在惯性约束聚变中的X光诊断等方面有着十分重要的应用。通过Geant4软件较为全面地分析了CsI(Tl)闪烁体软X光能量响应,模拟了1~5keV的软X光入射不同厚度(20,30,50μm)CsI(Tl)的能量沉积谱,探究了粒子之间相互作用的物理过程,并比较了不同能量软X光在不同厚度CsI(Tl)闪烁体中的沉积效率。仿真结果表明,随着CsI(Tl)闪烁体厚度的增加,软X光在CsI(Tl)闪烁体中沉积的能量也逐渐增加,沉积效率与CsI(Tl)闪烁体厚度成正比。模拟研究为选择合适厚度的闪烁体做低能段软X光探测实验做铺垫。     

硬X光弯晶谱仪的定量化标定方法

介绍了具有定量化测量能力的硬X光弯晶谱仪的结构, 利用Mo靶X光管的K特征线作为标定源, 使用绝对标定过的Si(Li)探测器对X光管出射的特征线谱进行强度和谱测量。结合X光管空间分布均匀的特点, 计算进入弯晶谱仪的光子数目, 采取了特征谱扣去轫致谱的计数处理方法, 得到了17 keV和19 keV处弯晶谱仪的绝对效率, 分别为4.3210-4和3.9410-4。     

Color centers in heavily irradiated CsI(Tl) crystals

The absorption and luminescence properties of CsI(Tl) crystals colored by irradiation are studied by the method of the time-resolved spectroscopy. The scheme of the electron transitions in CsI(Tl) crystal is suggested to explain the appearance of the color centers under exposure to the near-UV light. It is established that either of the two types activator color centers holds the charge carrier with opposite sign. The model of the hole Tl²⁺v_c⁻ activator color center is suggested. According to the model the positive charge of Tl²⁺ ion is compensated by the negative charge of a close cation vacancy v_c⁻. The color center emission reveals in the cathode-luminescence spectrum of the colored CsI(Tl) crystal. The high-dose irradiation of CsI(Tl) crystal results in the reduction of the decay time of the near-thallium self-trapped excitons (STE) emission. The decay kinetics of Tl²⁺v_c⁻ emission contains the time components typical for the decay kinetics of near-thallium STE emission. The reason of the observed effects is the energy transfer from the near-thallium STE excitons to the color centers via the inductive-resonant mechanism.     

用于辐射复合与双电子复合实验的低能离子闪烁探测器

为了在CSRm的电子冷却器上进行辐射复合以及双电子复合实验, 需要探测能量小于4 MeV/u的离子, 因此设计了新的置于超高真空环境的CsI(Tl)闪烁探测器, 探测器采用的光电倍增管为R7525(Hamamatsu）。 介绍了新闪烁探测器的结构, 并对其进行了性能测试。 测试结果表明, 该探测器对高、 低能离子均有良好的响应, 探测器的信号十分明显。 探测器的最高计数率可以达到106 ions/s, 并且探测器附近的真空度可达10-10 Pa量级, 能够满足辐射复合与双电子复合实验以及储存环对真空的要求, 为今后在CSRm上进行复合实验打下了良好的基础。 A new CsI(Tl) scintillation detector readout with R7525 PMT(Hamamatsu）is designed to detect low energy (<4 MeV/u) ions in radiative recombination and dielectronic recombination experiments at the main cooler storage ring in Lanzhou. The structure of the scintillator detector is described in this paper. The detector is tested with α source and ion beams, respectively. The signals from background, 200 MeV/u C6+ and alpha radioactive source are recorded and analyzed. The results show that the detector has good response to high and low energy ions. The maximum counting rate of the detector can reach 106 ions/s and the vacuum level near the detector can reach 10-10 Pa, both are good for recombination experiments. The installation of the new detector to CSRm is of great help for future radiative recombination and dielectronic recombination experiments.     

Energy resolution of CsI(Na) scintillators

The presented paper on CsI(Na) scintillators is a continuation of systematical studies of alkali halide crystals exhibiting more than one exponential decay time. The CsI(Na) crystals are known to have short (～550 ns) and long (few microseconds) components in the scintillation pulse. Previous studies showed that integration of slow components of the light pulse improved the light output, non-proportionality and energy resolution of CsI(Tl), NaI(Tl) in lower temperatures and undoped NaI crystal at liquid nitrogen temperature. In this work, an influence of the shaping time in the spectroscopy amplifier on the light output, non-proportional response to γ-rays, and energy resolution of two different size CsI(Na) scintillators is examined. Each crystal was coupled to the Photonis XP5212 PMT with a photocathode blue sensitivity of 12.2 μA/l mF. The data analysis showed improved proportionality of the crystal response, higher number of photoelectrons/MeV-γ, and consequently, a better overall energy resolution obtained for 12 μs shaping time constant. Finally, the CsI(Na) characteristics are compared to that obtained previously for NaI(Tl).     

工业CT光电二极管探测器灵敏度

在工业CT系统设计过程中,射线能量选择、探测器结构设计、射线源和探测器匹配等方面都涉及探测器灵敏度问题。研究了影响工业CT光电二极管探测器灵敏度的几个主要因素及其定量关系。首先分析了灵敏度的几个主要影响因素:能量沉积率、绝对闪烁效率、光收集效率、光电转换效率。然后采用蒙特卡罗方法仿真得到闪烁体的能量沉积率、光收集效率,计算了CsI(Tl)闪烁体的荧光转换效率及光电二极管的光电转换效率,定义了闪烁体与光电二极管的匹配度的概念。最后得出具有普遍意义的探测器灵敏度的表达式,理论计算值与实际测量结果最大相差20.4%,实验验证了该灵敏度计算方法的有效性和正确性。     

Data Acquisition System for the Calorimeter of the Belle II Detector

Physics of Atomic Nuclei - The electromagnetic CsI(Tl) calorimeter is one of the key systems in the Belle II detector. The calorimeter is aimed primarily at efficiently detecting photons over a...     

HXMT卫星地面样机成像实验

硬X射线调制望远镜(HXMT)致力于实现硬X射线能段的高灵敏度巡天.HXMT地面样机已在中国科学院高能物理研究所粒子天体物理重点实验室建成.它包括18个栅条准直的NaI(Tl)/CsI(Na)复合晶体探测器,总有效探测面积为5000cm². 探测器工作在20—250keV,视场范围5.7°×5.7°通过近距离放射源成像实验和直接解调成像方法的使用,地面样机能够达到2'点源定位精度和5'角分辨率(FWHM).