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 Silicon-Emulsion Shower Counter for Cosmic Ray High Energy Electron Observation

An instrument consisting of a combination of position sensitive silicon detectors, nuclear emulsion plates and lead plates is proposed for measurement of the energy of primary cosmic ray electrons with the energy of lower than 30 GeV. As position sensitive detector, two dimensional Si(Li) circular detectors with sensitive area of 38.5 cm2 have been fabricated and build-up curves (transition curves) of deposited energy in the detector versus thickness of lead plate for high energy electron beams are presented as fundamental data for design of such an instrument.     

Advantages of Response Function Change in a transXend Detector with Various Scintillators as Substrates of Segment Detectors

To enable practical computed tomography (CT) that uses the energy information of X-rays, the “transXend detector” was developed to provide energy information about incident X-rays by measuring them as an electric current. The transXend detector requires a spectrum survey method in the unfolding process for measuring the energy distribution of incident X-rays, when the response functions of segment detectors have nearly the same behavior. When employing various scintillators with different effective atomic numbers and densities as the substrates of the segment detectors, better convergence is obtained in the unfolding process by using only one initial guess spectrum. Additionally, less dose exposure is possible when using the transXend detector with various segment detectors, compared with the transXend detector that consists of the segment detectors with the same substrate.     

Transient Response of Surface Barrier Detectors as a Function of Fission Fragment Energy

The transient response of silicon surface barrier detectors to fission fragments of Cf252 was observed over a range of incident fragment energies from 13.6 to 90 MeV. From these observations the effect of the plasma formed by the incident particle on the charge collection time was determined. The time to disperse the plasma, tp, was calculated as a function of incident particle energy, Eo, and applied field, E. It was found that tp ? Eo1/m where 2 ? m ? 3 and tp ? E-1. A simple model gave reasonable agreement with the experiments and indicated that the plasma is dispersed by field-enhanced diffusion.     

Long-term measurements of equilibrium factor with electrochemically etched CR-39 SSNTD

Recently, our group proposed a method (proxy equilibrium factor method) using a bare LR 115 detector for long-term monitoring of the equilibrium factor. Due to the presence of an upper alpha-particle energy threshold for track formation in the LR 115 detector, the partial sensitivities to ²²²Rn, ²¹⁸Po and ²¹⁴Po were the same, which made possible measurements of a proxy equilibrium factor F_p that was well correlated with the equilibrium factor. In the present work, the method is extended to CR-39 detectors which have better-controlled etching properties but do not have an upper energy threshold. An exposed bare CR-39 detector is first pre-etched in 6.25 N NaOH solution at 70 °C for 6 h, and then etched electrochemically in a 6.25 N NaOH solution with ac voltage of 400 V (peak to peak) and 5 kHz applied across the detectors for 1 h at room temperature. Under these conditions, for tracks corresponding to incident angles larger than or equal to 50°, the treeing efficiency is 0% and 100% for incident energies smaller than and larger than 4 MeV, respectively. A simple method is then proposed to obtain the total number of tracks formed below the upper energy threshold of 4 MeV, from which the proxy equilibrium factor method can apply.     

Solar particle induced upsets in the TDRS-1 attitude control systemRAM during the October 1989 solar particle events

The three large solar particle events, beginning on October 19, 1989 and lasting approximately six days, were characterized by high fluences of solar protons and heavy ions at 1 AU. During these events, an abnormally large number of upsets (243) were observed in the random access memory of the attitude control system (ACS) control processing electronics (CPE) on-board the geosynchronous TDRS-1 (Telemetry and Data Relay Satellite). The RAR I unit affected was composed of eight Fairchild 93L422 memory chips. The Galileo spacecraft, launched on October 18, 1989 (one day prior to the solar particle events) observed the fluxes of heavy ions experienced by TDRS-1. Two solid-state detector telescopes on-board Galileo designed to measure heavy ion species and energy, were turned on during time periods within each of the three separate events. The heavy ion data have been modeled and the time history of the events reconstructed to estimate heavy ion fluences. These fluences were converted to effective LET spectra after transport through the estimated shielding distribution around the TDRS-1 ACS system. The number of single event upsets (SEU) expected was calculated by integrating the measured cross section for the Fairchild 93L422 memory chip with average effective LET spectrum. The expected number of heavy ion induced SEUs calculated was 176. GOES-7 proton data, observed during the solar particle events, were used to estimate the number of proton-induced SEUs by integrating the proton fluence spectrum incident on the memory chips, with the two-parameter Bendel cross section for proton SEUs     

p+~(107,109)Ag核反应数据的计算和分析

本工作通过理论计算的方法获得了一套适合入射能量为从阈值到200 MeV的p+107,109 Ag核反应全套微观数据。首先,使用光学模型理论进行调参计算,得到了一套适合入射能量为从阈值到340MeV的p+107,109 Ag核反应Becchetti-Greenlees光学势参数,这套参数与实验数据符合很好。其次,在这套光学势参数的基础上用扭曲波玻恩近似对入射能量从阈值到200MeV的p+107,109 Ag直接非弹性散射截面进行了计算。最后,使用核反应统计理论计算了入射能量从阈值到200MeV的p+107,109 Ag核反应各反应道的截面和出射粒子能谱,得到了该能区p+107,109 Ag核反应全套微观数据。将所有计算值与实验数据进行比较,结果表明,所得到的全套微观数据与实验数据符合很好。     

大面积阵列中子伽马甄别探测器的蒙特卡罗模拟研究

对特殊核材料的检测关乎国土安全,需要一个快速、安全可靠的辐射检测系统。采用Geant4蒙特卡罗模拟软件建立一套基于塑料闪烁体的大面积中子伽马探测系统。研究单根闪烁体晶体不同截面边长、多种层数结构以及不同natGd₂O₃包裹方式等探测器的关键参数,通过调整探测器的响应数目阈值评估探测器的n/γ甄别性能。结果表明,当采用截面边长为6 cm×6 cm的塑料闪烁体包裹25 μm厚的natGd₂O₃、探测器之间放置3 mm厚Pb板以及探测器响应数目阈值设置为3时,阵列探测器可以达到约23%的中子探测效率以及约802的n/γ甄别比。计算结果可对大面积阵列探测器的关键参数优化提供理论依据。     

Silicon detector response to heavy ions at energies of 1–2 MeV/amu

The response of silicon detectors has been measured for He, O, S, Cl, Br, Ag and Pb ions in the energy range 1–2 MeV/amu. Following deliberate, long exposures of the detector, a transient effect was observed for 140 MeV Br ions, in which the pulse height decreased with increasing ion dose and then partially recovered within an hour of the final exposure. Using brief, consecutive exposures, the effective energy for creating a detectable electron–hole pair was determined using the pulse height difference method. The energy deposited by ions in the ‘dead-layer' at the detector surface and energy loss via non-ionizing events was taken into account. For ions with atomic numbers 2Z17 and energies above the Bragg peak, the effective energy was found to decrease linearly with increasing electronic stopping power at first, and then to level off at 3.52 eV/electron–hole pair. For intermediate mass ions (17<Z40), at energies close to the Bragg peak, increases slightly (2%) with increasing stopping power. For the heaviest ions studied (Z40), whose energies are below the Bragg peak of the stopping power curve, increases strongly (10–20%), even though the electronic stopping power is approximately constant.     

Neutron response functions for superheated droplet detectors

Neutron response functions for superheated droplet detectors have been analyzed from threshold up to 2 MeV incident energy, taking into account a gradual threshold function, in terms of temperature and incident energy. A method for obtaining fitted parameters is described. Detection mechanisms up to 14 MeV are discussed     

Applications of Detectors in Low Energy Nuclear Physics

This review paper discusses new applications of detectors in low energy nuclear physics and emphasizes semiconductor particle detectors where new developments have had an outstanding influence on the nuclear physics which can be done. The paper includes an account of: new limits of detector resolution; a new method for measurement of gamma ray lifetimes; gamma-gamma angular correlation studies with multiple scintillation detectors; kinematic energy shift correction with radial position sensitive detectors; an improved particle identification system with multiple detectors; and the application of germanium to measurements of long-range charged particles. The paper also discusses present state-of-the-art limitations and possibilities in areas of particular importance to nuclear physics.     

Resolution and sensitivity as a function of energy and incident geometry for germanium detectors

The use of modeling programs such as MCNP to predict the response of HPGe detectors is increasing in importance. Accurate simulation of germanium detectors to incident gamma rays relies on knowledge of the performance of the detector in different detector–source geometries. Two important performance parameters are the resolution and sensitivity. The resolution is the FWHM and FW.1M/FWHM ratio. The IEEE 325-1996 standard only specifies the FWHM measurement at one geometry and two energies. Nearly all measurements are made in a different geometry and at other energies. Other investigators [Specifications for Today’s Coaxial HPGe Detectors, 2001 ANS Annual Meeting, Milwaukee, WI; Metzger, private communication, see also: Radionuclide Depth Distribution by Collimated Spectroscopy, 2002 ANS Topical Meeting, Santa Fe, NM], have shown that the sensitivity and resolution change with position of the incident gamma ray on the front of the detector. Such variability has possible implications for the accuracy of peak shape and area determination, since the calibration is potentially a function of angle of incidence. To quantify the sensitivity and resolution variation as a function of energy and point of incidence, measurements have been made on several coaxial detectors of various crystal types and sizes in different source–detector geometries. The full-energy peaks from 59 keV to 2.6 MeV were used. The detectors were placed in a low-background shield to reduce any contribution from external sources. None of the detectors tested was a low-background type. The sources used were an ²⁴¹Am source, ⁶⁰Co source and a natural thorium oxide sample. The ²⁴¹Am 59 keV gamma rays were collimated by a 2 cm thick, 1 mm diameter lead collimator. Several gamma rays from the thorium source were used and collimated by a 10 cm thick and 2 mm diameter tungsten collimator. These collimated sources were used to collect spectra for the incident beam on the front and sides of the detectors. The peak widths were calculated using the methods outlined in IEEE 325-1996. Data are presented to show that the peak shape and sensitivity change with incident beam position and full peak energy.     

Tory II-C Nuclear Instrumentation System

The design of the nuclear instrumentation system for the Pluto series of nuclear ramjet test reactors is an attempt to provide a very flexible nuclear sensing system that will be adequate for Tory II-C and following test reactors. The nuclear detectors will be exposed to the leakage neutron flux from the reactor during operation. Since the leakage flux is proportional to reactor power, the neutron detectors will give a measure of reactor power. A difficulty in providing nuclear instruments for this reactor is the uncertainty in the neutron energy spectrum of the leakage flux at the detectors. Since detector response varies with neutron energy, a large margin of flexibility is desirable. A difficulty which may be encountered is a significant shift in neutron energy spectrum at high power and temperature. This would make indicated nuclear power nonlinear with calorimetric power. A difficulty in insufficient instrument overlap was encountered with the Tory II-A experiment where a large margin of flexibility would have been useful. The detector placement for the Tory II-A experiment had the power range detectors in line with the reactor and main air pipe. At high air flows there was a much greater mass of air between the detectors and the reactor, allowing fewer neutrons to reach the detectors per unit reactor power. This is the reason for the power range detectors being placed off to the side of the Tory II-C test vehicle. Not all difficulties can be foreseen, but provision is made where possible to overcome them.     

Quantitative depth profiling of deuterium up to very large depths

Quantitative depth profiles of deuterium up to very large depths are achieved from the energy spectra of protons created by the D(³He,p)α nuclear reaction at incident energies up to 6 MeV. The advantages of this method compared to the more often applied resonance method are discussed. For light target materials the achievable depth resolution is mainly limited by geometrical spread due to the finite size of the detector aperture, while for heavy materials the resolution is mainly limited by multiple small-angle scattering. A reasonable depth resolution throughout the whole analyzed depth can be obtained by using several different incident energies. Depth profiling up to 38 μm is demonstrated for a-C:D layers deposited on the limiter of Tore Supra, and up to 7.5 μm in tungsten coatings from the divertor of ASDEX Upgrade.     

核活化法反应计算中的蒙特卡罗模拟

用MCNP/4B程序,对核活化法反应计算中的截断能量、通量计数方式、数据库、阈探测器之间的扰动等因素的影响作了分析.截断能量可选为有效反应阈能,不影响计算结果,但可减少计算时间.栅元通量计数方式稳定可靠,效率高,计算值略高.不同的数据库的计算结果可能有些差别.阈探测器之间的扰动对计算结果的影响很小.     

薄窗型多阳极气体探测器研究进展

薄窗型气体探测器是最近发展并用于低能量加速器质谱探测技术。该探测器的入射窗采用氮化硅膜,薄而均匀,分辨率高,目前已在低能量粒子探测技术中得到初步应用,显示出广泛的应用前景。本文主要从薄窗型气体探测器基本原理、薄氮化硅膜与Mylar膜的对比、不同质子数Z的低能量粒子脉冲高度对比、薄窗型气体探测器与硅探测器的对比,以及应用等方面进行阐述。     

Charge resolution of CR-39 plastic nuclear track detectors for intermediate energy heavy ions

The charge resolution (δZ) for heavy ions (nuclear charge: Z < 40) of 0.1-1 GeV/n energy in CR-39 plastic nuclear track detector (PNTD) and its dependence on etching time, and on projectile Z and energy were investigated and optimized as part of an effort to make precise measurements of projectile charge-changing cross sections. Two types of CR-39 PNTD, HARZLAS TD-1 and BARYOTRAK, were exposed to heavy ion beams with seven values of Z behind thick targets to produce projectile fragments. Following chemical etching (7 N NaOH at 70 °C) for varying etch times, δZ of the projectiles was determined for each detector type. A strong dependence of δZ on the amount of bulk etch (B) was seen. It was also observed that δZ can be remarkably improved with longer etching time as a function of B^−1/2, in accordance with the trend seen in other types of track detector such as glass nuclear track detector. However, for B ? 60 μm (30 h etching), saturation occurs and there is no further improvement in δZ. Analysis of the correlations between projectile Z, energy, detector response, and fluctuation of the response make it possible to develop a model to predict the δZ for projectiles of given Z and energy. The predicted and measured values of δZ show good agreement within 10%. We conclude that 4 ? Z ? 30 at intermediate energy can be identified with good δZ in these detectors. The predictive model will be used in designing future cross section measurement experiments.     

高能P-P对撞中的μ子探测——模拟探测

对一种适用于未来高能P-P对撞机上的探测器模型和质心能在16和40TeV的P-P对撞事例中进行了模拟。并把模拟的物理事例引进了模拟的探测器。 本文重点叙述了如何把物理事例和探测器衔接起来,如何利用该模拟系统“探测”粒子和测量它们的物理量。特别是对μ子的探测和测量。     

Nuclear track formation and skewness of particle trajectories in the target: A new perspective

It is discussed why track detectors such as CR-39 and CN-85, which are only composed of light elements, are highly sensitive and efficient compared with detectors such as glass and mica, which are partly or fully composed of heavier elements. Weak scattering of incident particles by light target atoms does not significantly deviate incident particles from their straight trajectories while the target atoms recoil considerably, damaging the detector. Heavier atoms scatter incident particles through wide angles, significantly deviating them from their straight paths while the target atoms recoil weakly, producing less damage. Simulations are presented to demonstrate these concepts about nuclear track formation.