七十年代初切伦科夫技术的发展

一、引 言 1934年发现切伦科夫辐射[1]以来,人们对它的性质从理论和实验上作了详尽研究[2,3].切伦科夫探测器成为高能物理实验中鉴别粒子最常用的工具.文献[4]综述了1973年前这类探测器在高能物理中的应用,本文介绍这一技术在七十年代的发展概貌. 切伦科夫辐射的基本关系是 cosθ(λ)=1[βn(λ)].(1)粒子运动的方向和速度β=V/c可由介质折射率n(λ)和辐射角θ(λ)唯一地确定.在折射率n的介质中,只有高于阈速度βth=1/n的带电粒子才产生辐射,利用这一特点区分阈速度以上和以下的粒子的探测器称阈式探测器.由[1]式容易求得 dβ/β=[tg2θ(dθ…     

光电探测器光谱响应实验中值得注意的一个问题

在《普通物理实验教学大纲》和《近代物理实验教学大纲》中,都列有关于光电探测器的实验项目(题目是《光电探测器特性》和《光电探测器的光谱响应曲线》)。这反映了光电子器件近年来的迅速发展及其在科学技术中日益增长的重要性。 光谱响应曲线是光电探测器的重要特性之一。用来进行这一实验的器件有真空光电管、光电倍增管、光电导管(光敏电阻)、半导体光电二极管、光电池、光敏晶体管、辐射热电偶堆等等。实验的基本原理是,对一定波长为人的光,光电流的强度I(λ)与单色辐射通量Φ(λ)成正比,即:用单色辐射通量Φ(λ)除所产生的光电流强度…     

一种高精度光纤测温系统工作波长的优化设计

基于基尔霍夫定律 ,利用钽酸锂热释电探测器设计了一种实用化的双波长、高精度光纤测温系统。依照测温系统中单个探测器的温度分辨力、R(T)～T曲线的线性度、R(T)～T曲线的温度灵敏度及其相对温度灵敏度与各主要技术参量之间的关系 ,对采用钽酸锂热释电探测器作光电转换器件实现的实用化实时测温系统的工作波长进行了优化设计。实验表明 ,在测温范围 4 0 0～ 130 0℃内 ,当系统工作在λ1=2 .1μm、λ2 =2 .3μm时 ,其温度灵敏度高于 1.0× 10 -4℃ -1,相对温度灵敏度不低于 0 9,测温精度不低于 0 15 %。均符合设计要求     

一种被动式单波长实时测温系统的优化设计

基于Kirchhoff定律,利用一面反射镜,设计了一种可同时测量发射率及温度的单波长实时测温系统.从系统的测温灵敏度、相对测温灵敏度、探测器的温度分辨力及系统的测温标准差与波长的关系出发,并结合大气对红外辐射的透射特性,优化了系统的工作波长; 从系统的抗反射辐射能力与波长带宽的关系出发,并结合探测器的最小可探测光功率要求,优化了系统的波长带宽.实验结果表明,当λ=0.80 μm、Δλ=20 nm时,在测温范围600~2 500℃内,系统的测温不确定度优于0.3%.     

热辐射基尔霍夫定律的一种教学方案

本文希望在论述基尔霍夫定律时有比较严密的形式. 设想用一根不导热的线将一个球形物体悬挂于真空腔中(图1),使腔壁保持恒定温度T,球体与腔壁只能通过辐射和吸收交换能量.该系统最终将达到热平衡,于是球体温度与腔壁温度相同.考虑球体表面上某面元,它受到的来自腔壁的光谱照度为e(λ,T),球体材料的吸收本领为a(λ,T),于是它对所有波长的总吸收通量密度为 再考虑到球体的光谱辐射度为r(λ,T),于是它对于所有波长的辐射度为于是得热平衡方程不失一般性,作等波长间隔划分,式(1)变为这是关于变元e(λn,T)的一个N元线性方程. 将上述球体A1依次…     

应用光学——光学系统设计指南

第十六章光电探测器和热探测器(续)16.1.5 光电扩散和光电子牵制效应设有一片匀质光电导体材料,辐射从其一面射入(波长λ<λ_0),如图16.5所示。此辐射将产生电子-空穴对,而电子-空穴对将从表面扩散出去。这个扩散电流已被用来测量辐照度,其方法有两种。 1.把光电导体放在磁场中,在它的两端就会产生电压,如图16.5所示。当上表面     

一种被动式辐射测温系统的波长及其带宽设计

介绍了采用PIN硅光电二极管作光接收器件实现的一种被动式实时测温系统。该系统主要由光学接收系统、信号放大与处理系统及显示系统三部分组成。从系统的相对测温灵敏度及探测器的温度分辨力与波长间的关系出发,结合大气对红外辐射的透射特性,确定了系统的工作波长;从系统的抗反射辐射能力出发,并结合探测器的最小可探测光功率要求,确定了系统的波长带宽。从P1、P2的测量不确定度出发,讨论了待测目标的发射率及温度的测量精度。结果表明,当λ=0.80μm、Δλ=20nm时,在测温范围600~2500℃内,系统的测温不确定度优于0.3%,满足设计要求。     

溴化镧闪烁体探测器性能及应用研究

LaBr3(Ce)探测器是一种新型闪烁体探测器,具有高光产额,高探测效率,高时间和空间分辨率,高能量分辨率,温度特性良好,抗辐射性能良好,操作简便等优点.从2001年以来,该探测器得到了迅速的研究和应用.LaBr3(Ce)探测器在核共振荧光检测、瞬发γ中子活化分析、爆炸物检测、核医学成像、环境辐射监测、空间辐射探测等方面的应用研究中取得了非常良好的效果.该探测器表现出优于以往用于这些领域的探测器的性能(例如NaI(Tl)探测器、BGO探测器、HPGe探测器等).介绍了LaBr3(Ce)探测器的性能及其应用研究进展,对代表性文献进行了简析和综述,阐明了其良好的应用前景.     

基于球面反射温阑的红外探测器变f数设计

制冷型红外探测器f数由冷阑尺寸和位置决定,在冷阑附近加温阑可以改变探测器f数,但是会引入大量杂散辐射.为解决这一问题,提出一种基于球面反射温阑的红外探测器变f数设计方法.建立了温阑红外辐射模型,分析普通平面温阑引入的杂散辐射及其对探测器性能的影响.在此基础上提出球面反射温阑的设计方法,通过改变表面形状和发射特性,降低温阑引入的杂散辐射,以保证探测器变f数后的性能.为验证本文方法,设计球面反射温阑和普通平面温阑改变某制冷型探测器f数,在高低温试验箱内进行辐射定标实验测量两种温阑引入的杂散辐射,比较二者对探测器的影响.分析和实验结果表明,球面反射温阑引入的杂散辐射远小于普通平面温阑,引入的噪声等效温差也较小,能够更好地保证红外系统的成像性能.     

d~3络合物零场分裂的双自旋-轨道耦合参数模型

建立了三角对称d~3络合物零场分裂的双自旋-轨道耦合参数模型,它包括了经典晶场模型的零场分裂公式所忽略的配体贡献D(ζ_p)以及配体与中心离子相互耦合贡献D(ζ_d,ζ_p)的两部份;讨论了在不同的ζ_p,ζ_d及λ_r的情况下D(ζ_p)及D(ζ_d,ζ_p)的相对大小;指出了在ζ_p.及λ_r较大的情况下双自旋-轨道(so)耦合参数模型才能给出合理的结果;作为该模型的应用,计算了VCl_2和VBr_2的零场分裂,验证了D(ζ_p)对VBr_2的零场分裂是不可忽略的,并给出了与实验一致的结果.     

Photoluminescence of gamma-, proton- and alpha-irradiated LiF detectors

Lithium fluoride (LiF), one of the most pervasive alkali halides in optical device research, is routinely used in optical data storage and radiation protection. LiF crystals may contain different aggregate defects produced by several types of ionizing radiation, with the number of defects being proportional to the cumulative radiation dose. Stimulation of irradiated LiF detectors by heating or with blue light causes thermoluminescence (TL) or photoluminescence (PL), respectively. We developed a new PL reader equipped with a blue light-emitting diode for stimulation and a Hamamatsu photomultiplier for registering green emissions, dedicated to examining LiF detectors as well as more broadly investigating TL/PL emission from standard LiF detectors irradiated with gamma rays, 60 MeV protons and alpha particles. The results confirmed very high efficiency PL signal from alpha-irradiated LiF detectors corresponding to their low efficiency after gamma irradiation, and vice versa for TL readout. Combining the TL and PL readouts permits us to discriminate between how different kinds of radiation affect efficiency in LiF detectors.     

非定域位势e-μr/r·e-μr′/r′·e-αR/R及e-μr/r·e-μr′/r′·e(-(β(r+r′))1/2·R))/R的Regge渐近行为

本文证明了两个物理上有兴趣的非定域位势e^-μr/r·e^-μr′/r′·e^-αR/R及e^-μr/r·e^-μr′/r′·e^{(-(β(r+r′))1/2·R)})/R的分波S矩阵元对动量变数k在除沿虚轴的割线(-∞i,0),(μi,∞i)的全平面,对角动量变数λ在右半平面Reλ>-1/2的半纯性和当k,λ分别趋于无穷大时的渐近性质。最后得到了Regge渐近行为。     

Advantages and disadvantages of luminescence dosimetry

Owing to their excellent dosimetric properties, luminescence detectors of ionizing radiation are now extensively applied in individual dosimetry services. The most frequently used personal dosemeters are based on Optically Stimulated Luminescence (OSL), radiophotoluminescence (RPL) or thermoluminescence (TL). Luminescence detectors have also found several applications in clinical dosimetry, especially around new radiation modalities in radiotherapy, such as Intensity Modulated Radiotherapy (IMRT) or ion beam radiotherapy. Requirements of luminescence detectors applied in individual and clinical dosimetry and some recent developments in luminescence of detectors and techniques leading to significant improvements of the functionality and accuracy of dosimetry systems are reviewed and discussed.     

The experimental and simulated LET spectrum and charge spectrum from CR-39 detectors exposed to irons near CRaTER at BNL

Human will be sooner or later return to the moon and will eventually travel to the planets near Earth. Space radiation hazards are an important concern for human space flight in deep space where galactic cosmic rays (GCR) and solar energetic particles are dominated and radiation is much stronger than that in LEO (Low Earth Orbit) because in deep space there is no magnetosphere to screen charged particle and no big planet nearby to shadow the spacecraft.Research indicates that the impact of particle radiation on humans depends strongly on the particles' linear energy transfer (LET) and the radiation risk is dominated by high LET radiation. Therefore, radiation research on high LET should be emphasized and conducted systematically so as to make radiation risk as low as reasonably achievable (ALARA) for astronauts.Radiation around the moon can be measured with silicon detectors and/or CR-39 plastic nuclear track detectors (PNTDs). At present stage the silicon detectors are one of the preferred active dosimeters which are sensitive to all LET and CR-39 detectors are the preferred passive dosimeters which are sensitive to high LET (≥5 keV/μm water). CR-39 PNTDs can be used as personal dosimeters for astronauts. Both the LET spectrum and the charge spectrum for charged particles in space can be measured with silicon detectors and CR-39 detectors.Calibrations for a detector system combined with the silicon detectors CRaTER (Cosmic Rays Telescope for the Effects of Radiation) from Boston University and Massachusetts Institute of Technology, and the CR-39 PNTDs from JSC (Johnson Space Center) – SRAG (Space Radiation Analysis Group) were conducted by exposing the detector system to the accelerator generated protons and heavy ions. US space mission for the radiation measurement around the moon using CRaTER was carried out in 2009.Results obtained from the calibration exposures indicate an excellent agreement between LET spectrum and charge spectrum measured with CR-39 detectors and simulated with PHITS (Particle and Heavy Ion Transport System).This paper introduces the LET spectrum method and charge spectrum method using CR-39 PNTDs and the Monte Carlo simulation method for CR-39 detectors, presents and compares the results measured with CR-39 PNTDs and simulated for CR-39 detectors exposed to heavy irons (600 MeV/n) in BNL (Brookhaven National Laboratory) in front and behind the CRaTER.     

Assessment of integrated solar ultraviolet radiation by PM-355 detectors

The increase in environmental solar UV radiation due to depletion of ozone layer is a recent challenge to human health (skin cancer and eye effects) in countries having clear skies. Therefore, applying integrated, passive and inexpensive techniques to assess solar UV radiation is very much essential. Measurements of environmental solar UV radiation in Dhahran, Saudi Arabia area were carried out for a period of two months in the summer period in 1996 using two techniques in parallel namely: passive nuclear track detectors and active solar UV radiometers. Some of the nuclear track detectors were mounted in different conditions such as: under shadow band, on solar tracking mechanism following the solar rays. Others were mounted on perpendicular, tilted and horizontal surfaces in sunlight. All detectors were attached to a wooden background of the same thickness (0.5 cm) to eliminate interference of the heat effect of various support materials and have uniformity of the support materials. The assessment was carried out for different periods extending from two to nine weeks continuously. The investigated period covered the hottest months in Saudi Arabia (July and August) when the sky was clear of clouds. The results indicate linear correlation between alpha track diameters and the integrated exposure to solar UV as measured by the solar UV radiometer for all nuclear track detector positions and orientations. The highest slope has been observed for the detectors placed on solar tracking mechanism following the solar rays and the lowest from detectors oriented under the shadow band on horizontal position (measuring the diffused UV radiation only). The results show that most of the measured UV radiation (60%) were from the diffused UV radiation. The characteristics of the upper layer of the detectors are changed after chemical etching very quickly, with increase in the exposure time to UV solar radiation at certain orientation. The results encourage the use of nuclear track detectors for environmental and personal solar UV dosimetry on a large scale in Saudi Arabia and similar hot and clear-sky countries.     

Neutron measurements using bubble detectors--terrestrial and space

Like all other radiation monitors currently used in the space program, the bubble detector (which has flown on several missions) was adapted from a technology that was developed for terrestrial radiation. Bubble detectors are the most recent technology for applications in personal neutron dosimetry. They are now regarded as a mature technology and are used in many countries as a neutron dosimeter of record with approval from the respective regulatory authorities. Extensive type testing and QA of bubble detectors has been done by numerous groups, many of these to show that bubble detectors meet national radiation protection requirements prior to their acceptance as a dosimeter of record. In fact, it has been stated "Only bubble detectors achieve a sufficiently low detection threshold (to meet ICRP-60 recommendations)..." (Portal and Dietze, 1992).     

Advances in gravitational radiation detection

New experiments are reported which improve our estimates of the bandwidth and energy flux of the observed radiation. These include search for coincident, sudden increases in power of newly instrumented detectors at 1661 Hertz and 1581 Hertz, at opposite ends of a 1000 kilometer baseline, and search for coincidences between outputs of detectors at 1661 Hertz and 5000 Hertz. Coincidences are observed for the detectors separated by 80 Hertz, implying a radiation bandwidth exceeding 80 Hertz.The new instrumentation is a modification of the earlier technique for bonding ferroelectric crystals to aluminium cylinders. Three detectors are fully operational with sensitivity one order better than earlier ones.Progress has been made in data retrieval employing a computer and magnetic tape. Earlier results on the coincidence rates and time delay experiments have been confirmed.A 1661 Hertz detector has been developed for operation at liquid helium temperatures. It is now undergoing tests at the Argonne National Laboratory.An experiment has been approved by NASA to employ the moon as a gravitational radiation detector. Equipment has been designed by Bendix and the University of Maryland for emplacement by the Apollo 17 astronauts.Supported in part by the U.S. National Science Foundation.Presented at the International Conference on Gravitation and Relativity, Copenhagen, 5–10 July, 1971.     

Silicon photodiodes as Thomson scattering detectors in experiments on the Tuman-3M tokamak and in bench experiments

Experiments on Thomson scattering in the Tuman-3M tokamak plasma with silicon photodiodes applied as radiation detectors are performed. Bench tests and numerical simulation are used to compare the efficiency of detector modules based on conventional and avalanche photodiodes in recording weak pulses of various durations against uniform background light. When the pulse duration increases to several hundreds of nanoseconds, the increase in sensitivity due to avalanche gain disappears. This is of importance for diagnosing the tokamak plasma, where the background radiation is relatively intense.     

THz radiation sensors

In the paper, issues associated with the development and exploitation of terahertz (THz) radiation detectors are discussed. The paper is written for those readers who desire an analysis of the latest developments in different type of THz radiation sensors (detectors), which play an increasing role in different areas of human activity (e.g., security, biological, drugs and explosions detection, imaging, astronomy applications, etc.). The basic physical phenomena and the recent progress in both direct and heterodyne detectors are discussed. More details concern Schottky barrier diodes, pair braking detectors, hot electron mixers, and field-effect transistor detectors. Also the operational conditions of THz detectors and their upper performance limits are discussed.     

Coherence of radiation as studied by multiple coincidences of photons and particles

Coincidences of photons and particles are measured by counting the number of events occurring simultaneously in two or more detectors. Coherent and incoherent radiation may have different behavior when the number of coincidence counts is studied with different arrangements of the coincidence detectors: the coincidence rate for the coherent radiation field, such as that obtained from a single-mode laser, is independent on the transverse separation between the detectors as long as the intensity of the radiation stays constant. On the other hand, with incoherent thermal radiation, using suitable monochromatization, the coincidence rate can show a significant bunching effect at detector separations smaller than the transverse coherence length. As a third alternative, photon antibunching may be observed if the radiation field is prepared in a number state, such as that available from resonance fluorescence of atoms, ions or molecules. If the time resolution of the detectors is not sufficient to resolve separate counts, corresponding effects can be observed in experiments, where the analog outputs of the detectors are multiplied to produce an intensity correlation signal. Intensity correlation and coincidence studies of photons and particles are reviewed in this report starting from the early experiments in the 1950’s and including recent work on X-ray coincidences and three-pion correlations. New results are presented for three- and four-photon coincidences at the X-ray wavelengths.