血糖无创检测光纤探测器设计

应用蒙特卡罗方法模拟了三层皮肤组织中光的传输和分布情况，模拟结果得出光经过皮肤组织漫反射后的出射位置分布和出射角度分布情况；根据此模拟结果，分析和设计了一种具有特殊结构的血糖无创检测光纤探测器，此探测器在表皮和收集光纤之间设置了一组反射镜面，大部分光经镜面反射后被收集光纤收集。此设计弥补了光纤数值孔径对探测器收集效率的限制。     

端面泵浦热传导各向异性激光棒的温度场

为了解决LD端面泵浦热传导各向异性激光介质产生的热效应问题,建立了端面绝热、侧面冷却的Nd:YVO_4晶体热模型.考虑到Nd:YVO_4为热传导各向异性材料,而光纤耦合LD输出光束有超高斯分布的特点,利用特征函数法和常数变异法得到了超高斯光束端面泵浦热传导各向异性激光介质温度场的一般解析表达式,并定量分析了超高斯泵浦光阶次、泵浦功率以及光斑尺寸对Nd:YVO_4晶体温度场的影响.研究结果表明,若LD输出功率为50 W,光学聚焦耦合器的传输效率为82%,用四阶超高斯光束端面泵浦掺钕离子质量分数为0.5%的Nd:YVO_4晶体时,泵浦面可获得528.95 ℃的最大温升.所得结果可用于LD端面泵浦热传导各向异性激光介质全固态激光器热稳腔的设计,对于提高激光器性能具有理论指导作用.     

新型组合式离子探测器

本离子探测器是由连续电子倍增管和闪烁探测器两部分组成的。国产BDT型陶瓷连续电子倍增管用作离子—电子转换和次级电子放大。闪烁晶体及光电倍增管等组成的闪烁探测器用来探测电子倍增管输出的电子束流。这种组合式离子探测器具有低噪声(10~(-21)安培)和优良的脉冲幅度分辨率等优点。在15千伏转换电压下可获得幅度为6伏的脉冲信号,探测灵敏度为10~(-19)安培。     

基于SiPM的阵列式X射线背散探测器设计

阵列式探测器是背散射成像设备能够小型化的关键。受限于光电转换器件的灵敏度和转换效率等因素,阵列式探测器设计一直进展缓慢。本文提出使用硅光电倍增管(SiPM)作为核心部件,并从准直器、闪烁晶体和光电转换元件进行阵列背散射探测器设计的新思路。利用X射线特征谱线建立仿真模型,确定闪烁体CSI厚度为1 mm;准直器设计为栅格状,栅格高度4 cm,间隔为6 mm;SiPM尺寸相应为6 mm×6 mm。根据设计结果完成了探测器单个组件的加工,通过实际实验验证设计结果,实验证明合理设计的SiPM可以满足本应用长时、低光照强度以及被探测物体的厚度变化范围较大的要求。     

室温辐射探测器用CdZnTe晶体生长及其器件制备

采用改进的垂直布里奇曼法生长了直径为60 mm的碲锌镉晶体,晶体利用率达到70%以上。晶体中Te沉淀/夹杂密度小于1×10-3cm2,电阻率达到4×1010Ω.cm。利用得到的晶体制备了平面型单元探测器,测量了对不同能量射线的分辨率,其中对241Amγ能谱的分辨率达到4.7%,对137Cs能谱的分辨率为4.2%。采用Hecht公式对探测器收集效率与偏压的关系进行了拟合,得到电子的迁移率与寿命乘积值达到2.3×10-3cm2/V。     

端面泵浦热传导各向异性激光棒温场特性研究

了解决LD端面泵浦热传导各向异性激光介质产生的热效应问题,建立了端面绝热、侧面冷却的Nd:YVO4晶体热模型。考虑到Nd:YVO4为热传导各向异性材料,而光纤耦合LD输出光束有着超高斯分布的特点,利用特征函数法和常数变异法得到了超高斯光束端面泵浦热传导各向异性激光介质温度场的一般解析表达式。并定量分析了超高斯泵浦光阶次、泵浦功率以及光斑尺寸对于Nd:YVO4晶体温度场的影响。新的各向异性介质热传导方程求解方法具有计算量小、精度高等特点。研究结果表明：若LD输出功率为30W,光学聚焦耦合器的传输效率为82%时,4阶超高斯光束端面泵浦掺钕离子质量分数为0.5%的Nd:YVO4晶体,泵浦面获得528.95C的最大温升。所得结果可用于LD端面泵浦热传导各向异性激光介质全固态激光器热稳腔的设计之中,对于提高激光器性能具有了理论指导作用。     

大动态范围闪烁晶体荧光模拟器的设计

针对暗物质粒子探测卫星(DMPES)锗酸铋(BGO)量能器探测单元的标定需要,设计了一种用发光二极管(LED)作为光源的闪烁晶体荧光模拟器。首先,利用光电倍增管(PMT)测量BGO晶体在宇宙线辐射下的荧光脉冲,对脉冲波形建模拟合,并将波形存储到可编程信号发生器中。然后,选择一种峰值波长与BGO晶体的荧光发射波长相近,且其光通量与工作电流的线性度较好的LED,设计LED驱动电路,令LED的工作电流与模拟器输入的模拟电压信号幅度成正比。最后,利用信号发生器输出模拟的BGO晶体荧光脉冲波形至驱动电路,使LED发光,并利用积分球将LED的荧光通过光纤均匀地输出到多个PMT。实验结果表明:模拟器光脉冲测试结果与对BGO晶体实际测试的结果相似,光强覆盖PMT的2,5,8个打拿极(Dynode)输出,动态范围达4.11×103倍,满足暗物质粒子探测卫星BGO量能器地面检测系统的需求。该荧光模拟器也可用于同类闪烁晶体探测器系统的检测和标定。     

LD泵浦的全固体绿激光器研究

主要论述了用激光二级管(LD)泵浦、内腔倍频的绿激光器的原理和结构。在激光阈值、斜效率的讨论中指出:当LD的泵浦光束在激光晶体中的尺寸越小,光功率密度越高,激光阈值就越低,转换效率就越高;在放大基波的结构中,激光腔镜对基波的反射度越高,基波的放大倍数就越大,转换效率就越高;重点讨论了内腔倍频激光器中的“绿光问题”,指出造成“绿光问题”是由于模式正交分量之间的和频效应与空间烧孔形成的横向饱和;用Poincare图分析了激光器中出现的混沌行为;对如何克服“绿光问题”,得到稳定激光输出提出了几种方案。针对LD的光形状是一个椭圆光锥,选择了用多组透镜准直、棱镜对扩束的泵浦光传输系统方案;对腔体、激光膜层作了概述,具体提出了用平凹腔结构,并把激光膜层直接做在晶体上,可以减少腔内损耗;对YAG-KTP,YVO₄-KTP组合的绿激光器作了研究。在内腔倍频YAG激光器中观察到的实验现象很好地附合理论结果。在YVO₄-KTP的绿激光器中,比内腔倍频YAG激光器较容易得到YAG-KTP组合绿激光器,最大连续输出功率为14.4mW,阈值15.0mW,光-光斜效率为4.1%.YVO₂-KTP绿激光器:最大连续输出120mW,阈值100mW,光-光斜效率为6.3%.     

V型腔激光器倍频晶体长度分析和实验研究

根据倍频光转换效率公式和腔内倍频的稳态条件,推导倍频光功率密度的最大值和最佳倍频晶体长度的表达式,计算了当腔内损耗为5%,以Nd:YVO4和Nd:YAG为激光晶体时KTP晶体的最佳长度,分别采用Nd:YAG和Nd:YVO4为激光晶体进行实验。在Nd:YVO4/10mmKTP实验中,当泵浦光为15W时,获得了2.67W绿光输出,光-光转换效率达17.8%。     

闪烁体衰减常数值的脉冲波形测量方法

根据闪烁体发光衰减规律和衰减时间常数的定义,建立了闪烁探测器电流输出波形后沿特征量与闪烁体发光衰减时间常数的简洁关系,提出用测量脉冲波形后沿获得闪烁体发光衰减常数的三种简易方法,给出了相应的简单估算公式;在脉冲辐射源场中,测量了新型CeF3闪烁体对快脉冲γ辐射源的时间响应波形,用测量的波形脉冲后沿得到了CeF3衰减常数值;这种方法测量的结果与国外同行其它测量方法得到的结果基本一致.     

Energy dependence of the relative light output of YAlO<Subscript>3</Subscript>:Ce,Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Ce,and YPO<Subscript>4</Subscript>:Ce scintillators

The nonlinear dependence of the relative light output on the energy deposited in single-crystal scintillation materials YAlO₃:Ce (YAP:Ce), Y₂SiO₅:Ce (YSO:Ce), and YPO₄:Ce (YPO:Ce) has been studied. The investigations have been conducted under quasi-monochromatic X-ray excitation in the energy range of 9.5–100 keV. In addition to the standard technique for measuring the nonproportional scintillator response based on the dependence of the full-energy peak position on the energy of incident radiation, a method is proposed for measuring the light output by X-ray fluorescence peaks. Using this method for YAP:Ce, it is possible to investigate the nonlinear dependence of the light output on the photon energy in the energy range of 2–40 keV. Along with this method, the K-dip spectroscopy method has been proposed and tested by measuring the dependence of the relative light output on the electron energy in the range of 0.1–80.0 keV. The processes resulting in the loss of the scintillation material efficiency at a high ionization density are considered.     

Extended algorithm for simulation of light transport in single crystal scintillation detectors for S(T)EM

The new extended Monte Carlo (MC) simulation method for photon transport in S(T)EM back scattered electron (BSE) scintillation detection systems of various shapes is presented in this paper. The method makes use of the random generation of photon emission from a scintillator luminescent centre and describes the trajectory of photons and the efficiency of their transport toward the photocathode of the photomultiplier tube. The paper explains a new algorithm for determining the position of interaction of the photon with the surface of the single crystal scintillator or of the light guide with nearly arbitrary shapes. Some examples of the utilization of the simulation method are also included, and conclusions for very simple edge-guided signal (EGS) scintillation detection systems made. The computer optimized design of the BSE scintillation detector for the S 4000 Hitachi SEM was chosen to demonstrate the capability of this MC simulation method.     

Application of accelerators for the research and development of scintillators

We introduce experimental systems which use accelerators to evaluate scintillation properties such as scintillation intensity, wavelength, and lifetime. A single crystal of good optical quality is often unavailable during early stages in the research and development (R&D) of new scintillator materials. Because of their beams' high excitation power and/or low penetration depth, accelerators facilitate estimation of the properties of early samples which may only be available as powders, thin films, and very small crystals. We constructed a scintillation spectrum measurement system that uses a Van de Graaff accelerator and an optical multichannel analyzer to estimate the relative scintillation intensity. In addition, we constructed a scintillation time profile measurement system that uses an electron linear accelerator and a femtosecond streak camera or a microchannel plate photomultiplier tube followed by a digital oscilloscope to determine the scintillation lifetimes. The time resolution is approximately 10 ps. The scintillation spectra or time profiles can be obtained in a significantly shorter acquisition time in comparison with that required by conventional measuring systems. The advantages of the systems described in this study can significantly promote the R&D of novel scintillator materials.     

A BSE scintillation detector in the (S)TEM

A single crystal YAG: Ce³⁺ annular scintillator axially placed in a movable light guide forms the essential part of a new BSE detector. Comparison of properties of this detector with those of a semiconductor detector is made. The bandwidth, signal-to-noise ratio, capacitance effects, and relative efficiency are parameters which favour the scintillation detector. Its disadvantage is that it must be equipped with a photomultiplier and a light guide. The position of the scintillator above the specimen permits efficient detection at a large collection angle of BSE. For normal beam incidence, the signal homogeneity from any area of the scintillator ensures that images are obtained without shadow effects due to signal loss in the scintillator or due to detector geometry. The same probe current as for other detection modes can be used. Resolution of details is as high as for an SE image.     

Studying kinetics of scintillation process in a CaMoO<Subscript>4</Subscript> crystal

The kinetics of scintillation process in Czochralski-grown CaMoO₄ crystals excited by α particles and γ rays from ²³⁸Pu and ¹³⁷Cs radioactive isotopes, respectively, is investigated. Kinetics of scintillations is shown to be complex and multicomponent in character. Fast and slow scintillation components are observed, and their relative contributions to the total light yield in the scintillator are determined. The possibility is demonstrated of discriminating between scintillator signals due to α particles and γ rays.     

A modification of the ET secondary electron detector with a single crystal scintillator

On the basis of the study of optical properties of single crystal YAG scintillators, it has been found that the maximum light output signal propagated in the required direction in the scintillator of a secondary electron detector is obtained if a cone-shaped scintillator is used. A modified Everhart-Thornley (ET) detector containing a conical scintillator and an electro-optical diaphragm operated at a positive voltage shows an increase to 2.8 times the light output signal of the classical ET detector with a flat single crystal YAG scintillator disc. The modification allows optimization of the suction of secondary electrons toward the scintillator and of the propagation of light from the scintillator toward the light guide.     

掺杂BaF2晶体闪烁性能的研究

在 BaF₂晶体中掺人 LaF₃,CeF₂,NaF 结晶出 BaF₂(La),BaF₂(Ce),BaF₂(Na)晶体,经测试,其中 BaF₂(La)晶体闪烁发光快成分的强度比纯 BaF₂晶体不减弱,而发光慢成分被抑制3倍,耐辐照能力可以达10⁶rad,表明新晶体有希望满足未来高能物理实验的要求。同时我们对 BaF₂晶体自身的损伤机制和闪烁机制进行了深入研究。     

Polystyrene and deuteropolystyrene plastic scintillators for a polarized active target

Results of light output measurements for a polystyrene scintillator deuterated to a degree of 96 at. % are presented. Applications of the deuterated scintillator are considered, in particular, as an active detector. In order to polarize the hydrogen nuclei in the scintillation target, a special additive, 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO), was introduced into it. This resulted in a light output of the sample with a thickness of 3.6 mm 50% that of the initial sample.     

Scintillation γ spectrometers for use at nuclear power plants (review)

In this review, it is shown that out of the 300 scintillators synthesized to date only LaBr₃:Ce, CeBr₃, YAlO₃: Ce, and CsI:Tl crystals with the corresponding silicon photosensors (SiPSs) can be used as detectors in industrial γ-ray spectrometers intended for nuclear power plants. They are superior in their energy resolution and their resistance to mechanical and electromagnetic effects to spectrometers used today with a NaI:Tl crystal and a photomultiplier tube (PMT). A p–i–n photodiode (PD), an avalanche photodiode (APD), and a silicon photomultiplier (SiPM) are promising SiPSs. The properties of various assemblies of listed scintillators and photosensors are analyzed. A PD matches well with any scintillator. A spectrometer does not require LED stabilization of the scale, but its noise level must be reduced by selective PD cooling and the use of a light guide for coupling a massive scintillator and a SiPS with a small area of its sensitive surface. A spectrometer with an APD does not require photosensor cooling; however, LED stabilization of its energy scale is necessary. Application of an SiPM can rule out the use of a light concentrator (which is important for large CsI:Tl scintillators) and selective cooling, but this introduces nonlinearity at a short decay time and a high light yield in the scintillator (LaBr₃:Ce and CeBr₃) and also calls for an LED stabilization system for the spectrometer. The prospects for the development and application of new scintillation γ-ray spectrometers are discussed in this review.     

Comparison of photon transport efficiency in simple scintillation electron detector configurations for scanning electron microscope

The purpose of this paper is to find some general rules for the design of robust scintillation electron detectors for a scanning electron microscope (SEM) that possesses an efficient light-guiding (LG) system. The paper offers some general instructions on how to avoid the improper design of highly inefficient LG configurations of the detectors. Attention was paid to the relevant optical properties of the scintillator, light guide, and other components used in the LG part of the scintillation detector. Utilizing the optical properties of the detector components, 3D Monte Carlo (MC) simulations of photon transport efficiency in the simple scintillation detector configurations were performed using the computer application called SCIUNI to assess shapes and dimensions of the LG part of the detector. The results of the simulation of both base-guided signal (BGS) configurations for SE detection and edge-guided signal (EGS) configurations for BSE detection are presented. It is demonstrated that the BGS configuration with a matted disc scintillator exit side connected to the cylindrical light guide without optical cement is almost always a sufficiently efficient system with a mean LG efficiency of about 20%. It is simulated that poorly designed EGS strip configurations have an extremely low mean LG efficiency of only 0.01%, which can significantly reduce detector performance. On the other hand, no simple nonoptimized EGS configuration with a light guide widening to a circular or square profile, with a polished cemented scintillator and with an indispensable hole in it has a mean LG efficiency lower than 6.5%.