Construction and Operation of an Electromagnetic Shower Detector

An electromagnetic shower detector consisting of lead glass blocks and scintillator hodoscopes was constructed. During calibration runs detector resolutions were measured for single incident electrons. Performance of the detector for ?° and multi-photon showers, including sizable backgrounds, was studied during actual data runs.     

Extended Capability for Fast Neutron Hodoscope Used at Treat

The fast neutron hodoscope used at TREAT reactor for fuel meltdown studies has been improved to permit count rates above 106/sec in each channel. Also a digital readout system, based on integrated circuit scalers, has been introduced. Peak instantaneous data rate capability, now about 107/sec, can be expanded to 109/sec.     

A Measurement of the Energy Resolution and Related Properties of an SCG1-C Scintillation Glass Shower Counter Array for 1-25 GeV Positrons

We report the measurement of the energy resolution of a 4×4 array of SCG1-C scintillation glass counters (Ohara Optical Glass Manufacturing Co., Ltd.) exposed to positrons in the energy range of 1 to 25 GeV. Each element of the array was 20.5 radiation lengths long. The resolution of the array was measured both with and without a 3.5 radiation length SCG1-C scintillation glass active converter and 0.2 radiation length hodoscopes used to measure shower position. We obtained an energy resolution ?/E = (1.63 + 1.46/?E)% without the active converter and ?/E = (0.64 + 3.94/?E)% with the active converter. Performing a partial correction for the average energy loss in the 0.2 radiation length hodoscopes resulted in an energy resolution of ?/E = (0.50 + 3.43/?/E)% for the active converter measurement. We also report on the measurement of the absolute number of photons produced by 1 GeV showers, the optical attenuation length for the light produced by showers, the fraction of the total light output that is due to Cerenkov light relative to scintillation light for showers, and the radiation darkening sensitivity of the scintillation glass.     

Study of PHOS Pre-shower Detector Performances

In the LHC/ALICE experiments, photon production will be studied with the PHOS electromagnetic calorimeter. A pre-shower detector has been proposed with a passive converter sandwiched by two MICROMEGAS detectors covering PHOS module to improve the photon identification, with respect to the set-up with only CPV in front of PHOS. The PPSD will considerably improve the rejection of neutral hadrons and the identification of overlapping showers.     

Avalanche Detector Arrays for in Vivo Measurement of Plutonium and Other Low Activity, Low Energy Emitters

Arrays of silicon avalanche detectors are being used for Ti vivo detection and measurement of low energy radiation in very small activities at room and body temperatures. Plutonium may be measured (via the 13.5-20 keV daughter uranium L x-rays) with an array of three 1 cm2 avalanche detectors in the esophagus, examining the thoracic lymph nodes which accumulate inhaled PuO2. The three detectors used in this array together provide uniformity of sensitivity to a source at any angle around the longitudinal axis of the array; using three independent signal processing systems, the array can also provide localization information. Plutonium scratches and puncture wounds may be inspected for contamination and the plutonium may be localized using a specially fabricated 1/8 inch diameter avalanche detector. With this configuration, the Minimum Detectable Amount (MDA) of Plutonium-238 (84% confidence level and four minute count) measured through 2 mm of tissue is 1 nCi. Early results of improved uniformity and resolution with the avalanche detector have shown promise of increased efficiency per unit area of detector face. A step toward unambiguous detection by making better use of the nanosecond speed of avalanche is described.     

新型望远镜带电粒子探测系统结构设计与理论模拟

为了在兰州重离子加速器国家实验室(HIRFL)的放射性束流线(RIBLL1)上开展基于完全运动学测量的远离β稳定线奇异核反应机制的研究,需研制一套由多个独立的望远镜系统(探测模块)组成的带电粒子探测阵列。每个探测模块包含1块16×16的厚65μm的双面硅条探测器、1块4×4的厚1 000μm的像素硅探测器和由雪崩光二极管(APD)读出的4×4CsI(Tl)阵列探测器。该探测阵列可实现大的能量测量范围、高能量分辨率和位置分辨,同时具备大立体角覆盖和粒子关联测量的能力。通过Geant4探测器模拟软件对单个探测模块进行模拟,结合对探测模块各部分的实验测试,给出了探测模块的设计方案和整体性能指标。     

角度灵敏平行板雪崩探测器及其应用

本文描述了其电极具有等距离分布的同心半圆环状窄条结构的位置灵敏平行板雪崩探测器(ASPD)的结构和工作原理。用此探测器可直接读出入射粒子的散射角θ和方位角φ以及时间信息。在流动的正庚烷气体中(气压950Pa)用~(241)Am α粒子对探测器进行了检验。得到θ方向角度分辨为Δθ=0.286°(对应于阴极平面上的径向位置分辨Δr=1.5mm),φ方向角度分辨Δφ=6°。时间分辨580ps。并给出了在串列静电加速器上被Au 靶弹性散射的α粒子的角分布的实验测量结果。     

电流型银激活探测器标定技术

为测量DPF脉冲中子产额,设计了电流型银激活探测器。该探测器由中子慢化体、天然银片、塑料闪烁体和光电倍增管组成。定义了该探测器测量DPF快脉冲中子产额时的探测灵敏度。采用高压倍加器稳态中子源对电流型银激活探测器的探测灵敏度进行了标定。稳态中子源的绝对中子产额由伴随粒子法给出。通过计算机自动记录探测器在饱和照射后其输出电流随时间的变化曲线,通过分析变化曲线求解特征参数,进而得到电流型银激活探测器在距离14 MeV脉冲中子源1 m处时的探测灵敏度为1.843´10⁹ nA^－1。在包含因子k为2时,探测灵敏度的扩展不确定度小于17.5 %。     

Pulse Height Dependence on Source Position in a Closed-End Coaxial Hyper-Pure Germanium Gamma-Ray Detector

The source position effect on peak center pulse height has been investigated on a 67cm3 closed-end coaxial hyper-pure germanium gamma-ray spectrometer. When a Na-22 source was moved on the axis of the detector, the peak center energy of 1274keV gamma-rays started to decrease at 20cm and a 44eV lower pulse height was observed at 1.5cm in front of the detector. The peak center energy did not change for moving the Na-22 source on a line(B) drawn through the detector center and perpendicular to the axis. The peak center energies observed for the source positions on the axis were lower than those observed on the line B, and the difference at 100cm distance was 15eV. This dependence is similar to that observed in a 73.2cm3 closed-end coaxial Ge(Li) detector reported by K. Shizuma, et al(JAERI-M 6497 (March 1976)). The shaping time of the main amplifier was 2?sec. The amount of the decrease in the pulse height at 1.5cm source-to-detector distance became smaller as the shaping time of the amplifier increased; the decrease was 178, 44, 24, and 10eV for the shaping time of 1, 2, 4, and 8?sec, respectively. The risetimes of the pulses were found to depend on the source position; the average risetime increased from 108nsec to 126nsec when the source moved from 30cm to 1.5cm in front of the detector. It is concluded that the risetime dependence on the source position is one of the origins which result in the pulse height dependence on the source position.     

一种高性能双维位置灵敏平行板雪崩探测器

本文描述了为兰州放射性离子束流线（RIBLL）研制的一种高性能平行板雪崩计数器（PPAC）。它由中心阳极和X、Y位置阴极构成，阳极间距3mm。阳极为1.5mm厚Mylar膜，双面镀金。阴极为φ25μm镀金钨丝，丝距1mm，位置读出采用电荷分除法。工作气体异丁烷。当工作气压为700Pa，阳极电压为500V时，对3组分α粒子位置分辨0.76mm(FWHM)，探测效率约99.1％。     

X射线纳秒时间分辨NIM电子学系统设计

主要介绍了一种用于X射线探测的纳秒时间分辨NIM电子学系统,并对该系统进行了功能测试、性能测试,得到了一些宝贵的是实验数据,为后续开展科学实验工作提供了参考。     

Initial test results of an ionization chamber shower detector for a LHC luminosity monitor

A novel segmented multigap pressurized gas ionization chamber is being developed for optimization of the luminosity of the Large Hadron Collider (LHC). The ionization chambers are to be installed in the front quadrupole and 0/spl deg/ neutral particle absorbers in the high luminosity interaction regions (IRs) and sample the energy deposited near the maxima of the hadronic/electromagnetic showers in these absorbers. The ionization chambers are instrumented with low noise, fast pulse-shaping electronics to be capable of resolving individual bunch crossings at 40 MHz. In this paper, we report the initial results of our second test of this instrumentation in a super proton synchrotron (SPS) external proton beam. Single 300 GeV protons are used to simulate the hadronic/electromagnetic showers produced by the forward collision products from the interaction regions of the LHC. The capability of instrumentation to measure the luminosity of individual bunches in a 40 MHz bunch train is demonstrated.     

直径30 cm的等高圆柱形载钆液闪探测性能

载钆液闪探测器是高能物理及核物理实验中重要的粒子探测工具。通过研制得到了一台大体积的直径为30 cm等高圆柱形载钆液闪探测器,载钆液闪溶液的载钆量为0.5%wt;利用252Cf中子源进行了中子与γ分辨性能实验测试,结果表明,直径30 cm等高圆柱形载钆液闪的中子与γ分辨性能较差;利用飞行时间技术通过符合测量的方法,分别测量了中子与伽马分辨谱中的中子与γ信号的时间分布,两者峰位之间的时间差为2 ns;利用252Cf裂变电离室的裂变碎片信号作为开门信号,通过符合测量的方法,获得了直径30 cm等高圆柱形载钆液闪的中子俘获时间分布实验数据,中子俘获平均时间为11μs。对于较大体积条件下,载钆液闪的中子与γ分辨性能较差的物理现象,通过实验给出了合理解释和分析。     

The Plastic Ball ? a Multi-Detector, Large Solid Angle Spectrometer with Charged Particle Identification for the Bevalac

For the study of central relativistic nuclear heavy ion collisions, which are characterized by the emission of a large number of particles, one needs a detector which covers a large solid angle ? 4? if possible ? and which is capable of identifying charged particles. The high multiplicity requires a large number of detectors, and the need for charged-particle identification requires a measurement of the energy loss, and the total energy for each particle detected. The spectrometer consists of 815 detector modules, which cover 94% of 4?. The geometry of these modules has been taken from the Stanford crystal ball detector for ?-rays ? with minor modifications. This geometry is suited for the high multiplicities of particles emitted in relativistic heavy ion collisions. The dimension of the individual elements have been chosen to stop 240 MeV protons. Above this energy reaction losses start to dominate, so that the light output of a scintillator would no longer be a true indication of the energy. Out of 100 charged particles, 94 will hit the Plastic Ball, 87 will fire a detector element, and 80 will be identified uniquely. For the individual detector modules we have used the "Phoswich" idea, by gluing a 4 mm thick CaF2 scintillator to a 35 cm thick plastic scintillator (NE114) with the shape of a truncated pyramid, which is viewed by one photomultiplier tube (PM2202B).     

A New Scintillator Tile/Fiber Preshower Detector for the CDF Central Calorimeter

A detector designed to measure early particle showers has been installed in front of the central Collider Detector at Fermilab (CDF) calorimeter at the Tevatron. This new preshower detector is based on scintillator tiles coupled to wavelength-shifting fibers read out by multianode photomultipliers and has a total of 3072 read-out channels. The replacement of the old gas detector was required due to an expected increase in instantaneous luminosity of the Tevatron collider in the next few years. Calorimeter coverage, jet energy resolution, and electron and photon identification are among the expected improvements. The final detector design, together with the R&D studies that led to the choice of scintillator and fiber, mechanical assembly, and quality control are presented. The detector was installed in the fall 2004 Tevatron shutdown and started collecting colliding beam data by the end of the same year. First measurements indicate a light yield of 12 photoelectrons/MIP, a more than two-fold increase over the design goals.     

Radiation Effects on Silicon Avalanche (Impatt) Diodes

The effects of fast neutrons with fluences up to 1016 n/cm2 on both dc and microwave characteristics of nearly abrupt X-band avalanche diodes have been studied. Good forward dc characteristics were observed up to 2×1015 n/cm2. At higher doses, the forward characteristics are degraded by the formation of a thin intrinsic layer at the metallurgical PN junction. The thickness of the intrinsic layer and its effects on device behavior could be reduced by reducing the depth of the diffused junction. At neutron fluences exceeding 4×1015 n/cm2, the avalanche breakdown voltage has a negative temperature dependence which results in a marked degradation in device reliability. The negative temperature coefficient is thought to be a result of an increase in the reverse saturation current or of changes in the field profile. Microwave oscillator characteristics - including oscillation threshold, power output, frequency, efficiency, and FM and AM noise - were virtually unchanged up to 1015 n/cm2. At neutron fluences greater than 1015 n/cm2, the oscillation threshold decreased and power output increased significantly (by 2 to 6 dB). The improvements are attributed to widening of the drift-field region and to a reduction in width of the unswept epitaxial parasitic resistance region. The greatest improvements occurred for the lowest-output power devices. These results suggest the use of nuclear radiation to tailor the defect concentrations and the field profiles of avalanche diodes to achieve optimal structures.     

LaBr_3(Ce)闪烁体APD前端读出设计

本文以雪崩光电二极管为小体积Labr_3(Ce)闪烁体的光电读出器件,并设计低噪声电荷灵敏前置放大器与雪崩光电二极管进行匹配组成完整前端探头,可应用于便携式小体积能谱仪中。雪崩光电二极管的增益、暗电流和结电容易受两端偏置电压影响,而这些特性的变化将影响能谱的读出效果。为此在不同的偏置电压下,测试了该探头组成的闪烁探测器的能量分辨率。当偏置电压为380 V时,对能量为662 keV的γ射线的最佳能量分辨为3.97%。     

Operating Characteristics and Applications of Multiwire Proportional Counters

Multiwire proportional counters have proved to be very useful for a wide variety of experiments at all energies. Properties of these detectors essential in planning an experiment, e.g. their efficiency as a function of position and their output timing, have been measured. Integrated circuit amplifier-discriminators have been developed for use with multiwire arrays and operated in the typical large accelerator environment. An experiment on the scattering of pions and protons by complex nuclei has been performed with 8-inch square arrays of proportional counters used for x, y hodoscopes.     

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。