光电倍增管线性电流扩展研究

根据对光电倍增管工作原理的分析,介绍了目前提高光电倍增管线性电流的方法,分析了不同类型的非线性效应.基于数字化示波器的应用和数据处理技术,提出了利用实验数据,通过数值校正的方法扩展光电倍增管的线性电流.利用线性电流大的光电管与光电倍增管进行比较,对光电倍增管通过校正,可以使光电倍增管的最大线性电流扩展5倍以上.     

光电倍增管对数十ms级宽脉冲信号的响应特性研究

提出了数十ms级宽脉冲信号的来源,探讨了光电倍增管响应失真的原因,给出了本实验光电倍增管的应用背景,搭建了宽脉冲信号实验平台,反复调整并测量了光电倍增管对于宽脉冲信号的响应特性,研究了一种测量光电倍增管对宽脉冲信号响应保真的方法,给宽脉冲中子探测器的研制奠定了基础,为宽脉冲中子探测领域的科研任务提供了重要参考。     

快响应门控光电倍增管设计

门响应时间和消光比是门控光电倍增管的两个重要性能参数。介绍了将俄制CHφT5型光电倍增管改制为门控光电倍增管的设计。采用控制光电倍增管第二聚焦极的方法,设计快响应门控制电路,使门控光电倍增管具有3个量级以上的消光比,开门延迟响应时间为70 ns,光电倍增管恢复输出的时间为20 ns。光电倍增管灵敏度降低了20%。     

光电倍增管老练对稳定性的影响

在闪烁计数、能谱分析和一些精密的光度测量中,光电倍增管的工作稳定性是很重要的。光电倍增管的稳定性实质上是光电倍增管的增益随时间的漂移——疲劳效应。产生疲劳效应的因素很多,一般与阴极倍增极材料、制造工艺、环境温度、使用条件及测量仪器精度等有关。实验证明,光电倍增管除了通过选取材料、改进制造工艺及选择最佳工作条件以提高其工作稳定性外,用老练的方法对部分管子克服疲劳效应改善工作稳定性是有一定成效的。     

精确测量光电倍增管最大脉冲线性参数的实验研究

李萨如图形法是测量光电倍增管最大脉冲线性参数的常用方法。本工作针对实验室使用李萨如图形法测量光电倍增管最大脉冲线性参数精度不高的问题,提出了使用恒流标定法确定李萨如图形的标准直线,进而给出了精确确定光电倍增管最大脉冲线性参数的方法及应用实例。结果表明：该方法有效降低了由判断标准直线引入的不确定因素,提高了光电倍增管最大脉冲线性参数的测量置信度,为高精度脉冲波形特征参数测量提供了必要的实验依据。     

大面积光电倍增管地磁场效应测试系统

大面积型光电倍增管(Photomultiplier Tube,PMT)广泛应用于各种高能物理实验中,但它对磁场比较敏感,在有地磁场的情况下实验结果的可靠性难以保证。为此,需要在电磁屏蔽间内放置高磁导率磁屏蔽罩定量屏蔽磁场,或在电磁屏蔽室缠绕三围螺线管线圈定量屏蔽地磁场。利用实验虚拟仪器工程平台,基于常用通信协议,建立了一套光电倍增管磁场效应在线测试系统,实现对光斑尺寸和磁场强度的自动调节,光电倍增管阳极信号的实时采集、存储和显示,可用于研究光电倍增管的地磁场效应。     

光电倍增管射频电磁辐射敏感性研究

分析了典型光电倍增管的电子束聚焦过程和射频电磁场对其干扰的机理,在此基础上利用脉冲光源和TEM小室设计了一套实验装置,开展了光电倍增管电磁辐射敏感性研究。在实验中通过观察光电倍增管计数率的变化,确定了其存在一个最敏感的干扰角度,找出了在此敏感角度下的干扰阈值和最易受干扰的频率点。最后对光电倍增管的两种电磁屏蔽措施进行了对比,给出了一种较为满意的设计方案,并应用于某型β射线探测器。     

正电子发射断层成像探测单元光电倍增管的增益调整

保持各个光电倍增管的增益一致性对正电子发射断层成像（PET）的质量至为重要。事件的响应输出取决于光电倍增管对于事件发生位置的光收集效率和事件的能量。光电倍增管对于某位置的光收集效率与光电倍增管对此位置所张的立体角成正比。当光电倍增管增益漂移后,通过计算出的各个管子的输出信号比值的变化完成对增益的自动调整,结果证明方法是有效的。     

团簇尺度的瑞利散射测量中光电倍增管信号刻度与归一化处理

利用光电倍增管测量团簇的瑞利散射,信号幅度与团簇源背压有关,也与光源强度和光电倍增管工作电压有关.当团簇源背压变化范围较大时,散射信号幅度变化可能导致光电倍增管信号超出线性范围.为此,在不同的光源强度、不同的工作电压下对光电倍增管输出信号进行了刻度,得到了输出信号幅度随光源强度、工作电压之间的关系.用此关系.对不同条件下的实验数据进行归一化处理,得到了团簇散射因子随团簇源背压的关系曲线,与同类实验和理论结果相符.     

光电倍增管中子直照响应实验研究

采用脉冲束中子飞行时间法和脉冲电荷计数法相结合的多参数测量方法,在中国原子能科学研究院HI-13串列加速器上,利用9Be(d,n)10B反应白光中子源,实验研究了光电倍增管对0.75～15MeV之间的出射中子直照灵敏度。根据光电倍增管的工作原理,采用MCNP程序模拟计算了光电倍增管的中子直照灵敏度。分析表明,计算结果与实验结果基本一致。     

Progress on Photomultipliers and Image Intensifiers at EMI Electronics Ltd.

This paper reviews recent work at E.M.I. on photomultiplier tubes. Dark current measurements by various techniques are presented, including data on tubes with high quantum efficiency and minimum thermionic emission suitable for low energy scintillation counting. Mention is made of a new fast tube, a small tube, and modified ion detectors. Two four-stage image intensifiers are described.     

Basic Limitation of Scintillation Counters in Time Measurements

The time resolution of a scintillation detector can be calculated from the scintillator illumination function, and the response of the photomultiplier to an instantaneous pulse of light. Such calculations using the parameters of present scintillators and photomultipliers agree with measured resolutions and predict improvements which can be achieved. Parameters of commercial and some promising experimental fast scintillators are given, as well as measurements on transit time spread of some fast photomultipliers.     

Relative Light Output Evaluation of Different Commercial Plastic Scintillators

An evaluation of light emitted from commercial plastic scintillators, when bombarded with radioactive particles, was done using photomultiplier tubes with S-11 and S-13 responses. Fourteen plastic scintillators, 1-in. long, were compared and eight different kinds were used to study light output as a function of length. It was found that light output does not fall exponentially with increasing length but rather as the sum of two exponents. A proposed method of analysis leads to two different absorption coefficients. Two possible explanations are given for this phenomenon.     

A Monte Carlo study of the timing resolution of BaF2 forTOF PET

A Monte Carlo study of the timing resolution of small BaF₂ crystals for time-of-flight (TOF) positron emission tomography (PET) is presented. The interaction of 511-keV gammas, the emission and transport of ultraviolet light in the crystal, and the pulse formation in the photomultiplier are simulated. The individual contributions to the timing resolution and the overall effect are calculated and compared to experimental measurements. It is found that for small crystal lengths the choice of photomultiplier can have strong effect on the resolution     

Negative Electron Affinity Materials in Photomultipliers

Since their introduction as laboratory devices about five years ago, negative electron affinity (NEA) electron emitters have found many applications for low-light-level detection. Over forty types of photomultiplier tubes with NEA materials are now available for detection of light from the ultraviolet to the near infrared. These devices provide useful photosensitivity to 1.1 micrometers. The detectors which are currently available will be reviewed, and the prospects for the near future will be discussed. A general summary of the contribution of NEA materials to low-light-level detection will be included.     

Photomultiplier Selection Criteria for Satellite Experiments

Forty-six RCA C 7151 Q photomultiplier tubes and thirty-five EMI 9711 NB photomultiplier tubes have been tested for use in the telescope of the COS-B gamma-ray experiment. The tubes were selected taking into account gain, linearity, fatigue behaviour and temperature characteristics. Besides identifying the most suitable tubes for this application, the experimentally determined values make it possible to derive "typical" behaviour parameters which can be used to pre-select tubes at the ordering stage. The results obtained with the EMI tubes clearly demonstrate a striking difference between "typical" catalogue values and "typical" measured values for the batch tested.     

Phase Doppler anemometer: commissioning tests for measurement of water aerosol sizes and velocities in flashing jets

A state-of-the-art phase Doppler Anemometer (PDA) has been commissioned at AECL Research, Whiteshell Laboratories to undertake the measurement of size and velocity of water droplets generated in flashing jets. Experimental data on size and velocity distribution of water aerosols in flashing jets are required to support licensing of current multiple-unit and single-unit Canada deuteruim uranium stations. This paper presents the methodology involved in choosing the magnitudes of the various operating parameters of the PDA such as laser power and sensitivity of photomultiplier tubes in obtaining the experimental data. The various calibration and validation procedures used are also discussed. Size and velocity distributions in a typical flashing jet are presented.     

Time Resolution Measurements with Fast Photomultipliers

A comparision of experimental data and theoretical predictions on time resolution limits of fast photomultipliers has been performed. XP 1020 photomultipliers have been used and measurements were done with a fast electronic system built in our laboratory. This system was tested with a Co60 source, the best time resolutions achieved over a period of two hours being 164 psec at f.w.h.m. A hydrogen discharge lamp has been built which produced short light pulses whose shape is determinated by a sampling method. Several light intensities were used to simulate different energy losses in plastic scintillators and time resolution measurements were performed for different threshold settings of the discriminator. The results of these measurements were compared to theoretical data calculated by means of a statistical model of the photomultiplier. Good agreement was found assuming a photoelectronic yield of one photoelectron per 2.5 KeV in Naton 136 plastic scintillator and a single electron response (SER) variance of 500 psec. The necessity of having more accurate data on photomultiplier parameters, mainly concerning the transit time jitter, was pointed out in order to have a better understanding of the photomultiplier's behaviour.