Performance of a Thallium Chloride Scintiliator as a Total Absorption Shower Cascade Detector

Studies have been made of the performance of a large sample of the new heavy scintillator TlCl(Be,I) as a total absorption shower cascade (TASC) detector for high energy electrons and gamma rays. The observed energy resolution for electrons in the range 0.1 to 15 GeV is reported and compared to a Monte Carlo calculation of expected fluctuations in energy leakage from the crystal volume. The performance of this new scintillator and its potential applications are discussed.     

A precision synchrotron radiation detector using phosphorescentscreens

A precision detector to measure synchrotron radiation beam positions is described. It has been designed and installed as part of the beam energy spectrometers at the Stanford Linear Collider (SLC). The distance between pairs of synchrotron radiation beams is measured absolutely to better than 28 μm on a pulse-to-pulse basis. This contributes less than 5 MeV to the error in measuring SLC beam energies (approximately 50 GeV). A system of high-resolution video cameras viewing precisely aligned fiducial wire arrays overlaying phosphorescent screens has achieved this accuracy     

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.     

基于超高分辨γ射线探测器的蒙特卡罗模拟

能量分辨率是γ射线探测器关键技术指标之一,直接关联γ射线全能峰的尖锐程度、分离程度,从而影响全能峰被识别、区分的能力。提高γ探测器的能量分辨率,是γ探测器发展的一个重要方向,近年发展起来的超高分辨γ射线探测器,能达到25 e V@103 ke V的能量分辨率,其相对目前能量分辨率最好的高纯锗探测器的能量分辨率高一个数量级,因此超高分辨超导γ射线探测器成为了一大研究热点。为了推动超高分辨率γ探测器关键技术的实验研究,利用MCNP5采用了不同能量的射线源、不同规格的吸收体以及不同的支撑环境对超高分辨超导γ射线探测器的探测结果进行了模拟。这些模拟对于探测器的模型优化以及谱仪的设计有重要的指导作用。     

A Well-Type Ge(Li) Detector

The feasibility and usefulness of a coaxial Ge(Li) spectrometer as a well-type detector for sum spectra of coincident gamma rays is demonstrated. The value of the welltype geometry has previously been established in nuclear gamma spectroscopy with the use of (NaI(Tl) detectors. In this work a 16 cm3 hollow cylindrical germaniun detector has been made and mounted in such a way that access to the center of the detector is achieved from outside the cryostat. The detector is a fully depleted structure in which a hole of 1 cm diameter was ultrasonically cut, and a non-injecting contact applied to the inside surface. The measured resolution of the detector for a 1173 keV gamma ray sum peak from 144Pm was 2.6 keV f.w.h.m, which was mainly limited by statistics and preamplifier noise. The detection of sum lines arising from 2 or more coincident gamma rays is demonstrated by using the radioactive source of 144pm. With the source inside the well, for which the counting solid angle is nearly 4?, the sum peak of three lines at 1791 keV (696 + 618 + 477) was observed with an energy resolution of 3.5 keV f.w.h.m, and a peak to background ratio greater than 15:1. For the source outside the detector at a distance of 10 cm, this sum line was not observed above background for comparable counting statistics. Comparison is also made to results obtained from a 3" well-type NaI(Tl) crystal.     

叠层式探测器响应函数的理论计算和实验验证

光子能谱是脉冲辐射场中的重要参数.叠层式组合探测器可用于测量脉冲辐射场光子注量谱,而组合探测器对各种不同能量的光子的响应函数是光子能谱解谱的基础.本文用MCNP/4C对其响应函数进行了模拟计算,并采用热释光探测技术对典型能量点的γ射线的响应函数进行了实验验证.结果表明,叠层式组合探测器响应函数的理论模拟值和实验测量结果在实验测定精度内符合良好.     

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.     

国产LaCl3:Ce探测器裂变γ能区多能量点灵敏度测量

应用⁶⁰Co强γ源进行康普顿散射,再结合0.67 MeV（¹³⁷Cs源）和1.25 MeV（⁶⁰Co源）标准γ源,获得裂变γ能区多种能量γ辐射。以国产掺铈氯化镧（LaCl₃:Ce）闪烁晶体样品配光电倍增管构成快响应闪烁探测器,在这些γ能量下对LaCl₃:Ce探测器灵敏度进行了测量。测量结果表明：以LaCl₃:Ce对0.67 MeV γ的灵敏度为归一基准,LaCl₃:Ce对1.25 MeV γ的灵敏度约为1.28;对尺寸为f40 mm×2 mm的LaCl₃:Ce,能量在0.39～0.78 MeV之间对应的灵敏度最大为1.18,最小为0.96;对尺寸为f40 mm×10 mm的LaCl₃:Ce,最大为1.06,最小为0.98。本测量数据可为理论计算LaCl₃:Ce能量响应定标、校正提供测量数据参考,为获得裂变γ能区LaCl₃:Ce探测器综合灵敏度提供实验数据依据。     

核电厂运行现场高能γ射线的剂量调查

在核电厂正常运行期间,反应堆冷却剂系统内存在能够发射高能γ射线的¹⁶N等放射性核素。为了初步掌握核电厂运行期间不同区域内高能γ射线的辐射水平,利用NaI(Tl)谱仪在国内某核电站测量了反应堆厂房内的γ能谱,并根据γ测量谱和测量系统的响应函数计算了能量大于3 MeV的γ射线的场所剂量率。结果显示:在15个测量位置中,6个位置的γ测量谱中存在明显的高能成分,其对应的剂量率在1.02～30.14 μSv/h范围内。     

ST401闪烁探测器γ能量响应的实验研究

对脉冲γ射线束测量中常用的一种由塑料闪烁体ST401组成的电流型闪烁探测器的γ能量响应进行了实验研究。利用反应堆、加速器等多种手段产生一系列准单能的γ射线,实验标定了包括¹³⁷Cs、⁶⁰Co在内的13个能量点,得到了ST401闪烁体相对灵敏度随入射γ射线能量的变化曲线。实验值与理论计算结果进行了比较,二者在不确定度范围内基本一致。     

Gamma ray production cross sections from the bombardment of Mg, Al, Si, Ca and Fe with medium energy neutrons

Gamma ray production cross sections for the stronger gamma rays from nuclei excited by neutron bombardment of Mg, Al, Si, Ca and Fe have been measured using a time analyzed, quasi-mono-energetic neutron beam and a high-purity germanium detector. The results for neutron energies of 6.5, 17.4, 22.2, 32.5, 42.1 and 64.5 MeV are presented.     

Evaluation of prompt fission gamma rays for use in simulating nuclear safeguard measurements

Nondestructive assay methods that rely on measurement of correlated gamma rays from fission have been proposed as a means to determine the mass of fissile materials. Sensitivity studies for such measurements will require knowledge of the multiplicity of prompt gamma rays from fission; however, a very limited number of multiplicity distributions have been measured. A method is proposed to estimate the average number of gamma rays from any fission process by using the correlation of neutron and gamma emission in fission. Using this method, models for the total prompt gamma ray energy from fission adequately reproduce the measured value for thermal neutron induced fission of ²³³U. Likewise, the average energy of prompt gamma rays from fission has been adequately estimated using a simple linear model. Additionally, a method to estimate the multiplicity distribution of prompt gamma rays from fission is proposed based on a measured distribution for ²⁵²Cf. These methods are only approximate at best and should only be used for sensitivity studies. Measurements of the multiplicity distribution of prompt gamma rays from fission should be performed to determine the adequacy of the models proposed in this article.     

可作为校准检定用标准剂量计的能量补偿型高气压电离室改进

在电离辐射计量检定工作中,标准剂量计的测量结果通过检定逐级传递到工作计量器具,以实现单位统一和量值准确可靠。由于环境水平γ射线剂量率较低,国际上常用的PTW-UNIDOS系列标准剂量计无法满足需要。针对这一特点,结合蒙特卡罗方法对高气压电离室的X射线、γ射线和宇宙射线响应特性进行模拟计算,进行了能量补偿型高气压电离室改进。测试结果表明:剂量率约30 μGy/h时,能量补偿型高气压电离室在87 keV～1.25 MeV能量范围内相对于¹³⁷Cs γ射线的响应偏差不大于6%,宇宙射线和¹³⁷Cs γ射线的响应偏差不大于10%,在0.5 μGy/h～1 mGy/h范围内相对固有误差为-3%,0.5 μGy/h时的重复性为0.7%,校准因子的不确定度为4%(k=2),可作为环境水平标准剂量计在校准检定工作中使用。     

基于微通道板的电离室及其在同步辐射中的应用

在同步辐射装置中,气体电离室是定标光束线能量和评估能量分辨率的一个重要实验装置。为了摆脱电极探针式电离室的气体展宽对束线能量分辨率测定的限制,本文将微通道板(Microchannel Plate,MCP)应用于同步辐射光束线中的电离室,研制成功了具有高能量分辨率的电离吸收谱的探测系统。利用此系统测量标准气体在X射线入射时的电离吸收谱,通过分析测量所得谱线中吸收峰的展宽,可获得光束线的仪器展宽,本文以Ar的吸收谱为例给出了测量结果。     

TOF-PET探测器定时性能初步研究

本工作采用LYSO晶体阵列和平板型位置灵敏光电倍增管H8500对TOF-PET探测器进行了初步设计,能分辨3.2mm×3.2mm的晶体阵列。与BaF₂探测器组成时间谱仪,测量正电子湮没射线的瞬发时间谱,得到379ps的符合时间分辨率。根据已测量的BaF₂探测器时间分辨率（159ps）,可计算得到所设计的TOF-PET探测器时间分辨率为344ps。预计与此相同的两个TOF-PET探测器对正电子湮没射线的符合时间分辨率可达486ps左右,为新型PET的研究提供了有利条件。     

Basic consideration of a nuclear power monitoring system using neutron-induced prompt gamma rays

ABSTRACT

Monitoring only neutron flux in a nuclear reactor core has an advantage of offering reactor power monitoring accuracy. We started the development of a new nuclear instrumentation based on the measurement of prompt gamma rays emitted from metals placed at the neutron flux monitoring positions. The thermal neutron flux at the position of each placed metal piece can be monitored by measuring the prompt gamma rays as the count rate of each energy. The gamma-ray energy range was limited from 6 to 10 MeV to mitigate the interference of environmental gamma rays. Four metals, Ti, V, Ni, and Cu, were chosen as candidates in consideration of their neutron emission rates and self-absorption. In an experiment with a high-purity germanium semiconductor detector, we considered the identification of individual peak energies in an assumed situation where prompt gamma rays were emitted from the four different metals at the same time. Energy resolutions of the peak with the largest energy gap from the nearest energy peak of the other candidate metals were smaller than the gap. Thus, we confirmed that at least one peak for each candidate metal was able to be separated from the peaks derived from other candidate metals.     

瞬发伽玛活化分析中3种探测器性能比较

利用中国先进研究堆(CARR)热中子束流孔道首次开展了瞬发伽玛中子活化分析(PGNAA)实验。对NH4Cl、Si、Fe、Al等4种样品进行了辐照,同时采用HPGe、LaBr_3、BGO 3种探测器对样品进行实时测量,在瞬发伽玛射线的能量为0.002~10 MeV范围内研究了3种探测器在宽能区的能量线性、能量分辨率、探测效率等性能。     

蒙特卡罗方法在γ剂量率灵敏度标定中的应用

在γ剂量率测量标定中，使用ＧＤ－４０管作为γ探头来测量γ剂量率。实验室标定γ探头灵敏度在钴源上进行，６０Ｇｏ源平均能量为１．２５ＭｅＶ，而在实际测量中，辐射场的γ射线包含了各种能量成份，因此对实验室标定的灵敏度在实际应用中就需要进行修正。本工作通过蒙特卡罗粒子输运模拟方法，计算了单能与辐射场能谱的剂量比值，给出了修正因子，从而使γ剂量率灵敏度标定更加准确。     

A novel compact Tokamak Hard X-ray diagnostic detector

A compact X-ray detector based on the lutetium yttrium oxyorthosilicate scintillator(LYSO) and silicon photomultiplier(Si PM) has been designed and fabricated for the hard X-ray diagnosis on the HL_2A and HL_2M Tokamak devices. The LYSO scintillator and Si PM in small dimensions were combined in a heat shrink tube package, making the detector compact and integrative. The Monte Carlo particle transport simulation tool,Geant4, was utilized for the design of the detector for the hard X-ray from 10 keV to 200 keV and the best structure scheme was presented. Finally, the detector was used to measure the photon spectrum of a ~(137)Cs gamma source with a pre-amplifier and a multichannel amplitude analyzer. The measured spectrum is consistent with the theoretic spectrum, it has shown that the energy resolution of the detector is less than 14.8% at an energy of 662 keV.     

Annular gas ionization detector for low energy heavy ion backscattering spectrometry

A gas ionization chamber for use in backscattering spectrometry has been built. It has the shape of a hollow cylinder and can be placed in-line with the incident ion beam. The entrance window for detected particles is composed of a circular array of silicon nitride membranes. A low noise preamplifier with cooled FET is used for charge amplification. The detector resolution has been measured for a variety of ions in the mass range from He to Si and for energies between 0.5 and 8 MeV. The energy resolution of the ionization chamber surpasses the one of a state-of-the-art silicon charged particle detector for all ions heavier than Li. For Si ions the improvement in resolution is more than a factor of 2. The device does not suffer from any radiation damage. For He particles around 1 MeV the resolution is between 13 and 16 keV (FWHM). Therefore the new detector is not only well suited for heavy ion backscattering spectrometry but can also be applied for standard He RBS, allowing the use of a single detector for all types of projectiles in a wide energy range.