Current Methods for Laboratory Analysis of Environmental Levels of Radioactivity

This paper reviews the current methods for laboratory analysis of environmental levels of radioactivity and discusses the background, Compton scatter, and efficiency parameters that are associated with the various spectrometer systems. The methods which are discussed are: 1) total absorption gamma-ray spectrometry, 2) multidimensional gamma-ray spectrometry, and 3) multidimensional gamma-ray spectrometry with dual beta coincidence (all systems use NaI(Tl) detectors). Dual Ge(Li) anticoincidence shielded systems as well as NaI(Tl) and Ge(Li) coincidence gamma-ray spectrometers are discussed. The analysis of X-ray and alpha emitters is pursued for both laboratory and field detector systems. The special adaptation of some gamma-ray, X-ray and alpha spectroscopy systems to field utilization including underwater analysis is presented.     

Wafer-Bonded Silicon Gamma-Ray Detectors

A wafer-bonded silicon power transistor has been shown to function as an x-ray detector. The device consists of two thin device wafers bonded onto either side of a 2 mm-thick high-resistivity silicon wafer. The hydrophobic bonding process was performed at 400deg C. This low temperature wafer bonding technique should enable the development of large-area, position-sensitive detectors, using thick, high-resistivity intrinsic silicon bonded to thin readout wafers fabricated using conventional CMOS technology. These devices should enable fabrication of thicker intrinsic silicon detectors than currently available. Thick, position-sensitive detectors based on double-sided strip detectors and pixellated detectors are possible. To demonstrate this, a 1 mm thick gamma-ray detector was created from two 0.5 mm thick wafers that were patterned with gamma-ray strip detectors. The energy resolution of the detector is 8.9 keV FWHM for 60 keV gamma rays at room temperature with a leakage of 0.9 nA while operating at 700 V and fully depleted. Improvements in the technique should allow for thicker detectors with better energy resolution.     

An inversion decomposition method for better energy resolution of NaI(Tl) scintillation detectors based on a Gaussian response matrix

NaI(T1) scintillation detectors have been widely applied for gamma-ray spectrum measurements owing to advantages such as high detection efficiency and low price.However,the mitigation of the limited energy resolution of these detectors,which detracts from an accurate analysis of the instrument spectra obtained,remains a crucial need.Based on the physical properties and spectrum formation processes of NaI(T1) scintillation detectors,the detector response to gamma photons with different energies is represented by photopeaks that are approximately Gaussian in shape with unique full-width-at-half-maximum(FWHM) values.The FWHM is established as a detector parameter based on resolution calibrations and is used in the construction of a general Gaussian response matrix,which is employed for the inverse decomposition of gamma spectra obtained from the detector.The Gold and Boosted Gold iterative algorithms are employed to accelerate the decomposition of the measured spectrum.Tests of the inverse decomposition method on multiple simulated overlapping peaks and on experimentally obtained U and Th radionuclide series spectra verify the practicability of the method,particularly in the low-energy region of the spectrum,providing for the accurate qualitative and quantitative analysis of radionuclides.     

采用基于标准谱的热中子俘获瞬发活化伽玛分析方法分析NaCl水溶液

使用ＮａＩ（Ｔｌ）等能量分辨率较低但探测效率高的探测器在复杂环境进行在线热中子瞬发活化伽玛分析时宜采用基于标准谱分析方法。该方法包括标准谱完全集的获得，加权最小二乘解谱，灵敏度及归一化参数刻度等关键环节。我们采用ＮａＩ（Ｔｌ）探测器，使用＾２５２Ｃｆ中子源，对ＮａＣｌ水溶液进行了分析，获得了较好的精度。     

Resolution in large rectangular NaI(Tl) detectors: a study

Experiments were carried out for studying the resolution of 4-in (10-cm)×4-in (10-cm)×16-in (40-cm) NaI(Tl) detectors used in high-sensitivity airborne gamma-ray spectrometric surveys. Change of resolution with source-detector geometry emphasized the inadequacy of existing specifications for resolution in explaining the detector response. An additional specification for resolution measurement, namely, overall resolution, is proposed. Measurement and applications of overall resolution of the detector are discussed     

HPXe电离室和LaCl3(Ce)探测器在核材料鉴别中的应用

在核材料鉴别中，鉴于铀、钚材料中同位素种类多，发射的多条γ射线能量比较集中（主要都在0．1～2MeV之间）且分支比都比较小，生成的γ能谱复杂等特点，对于测量铀、钚材料的γ探测器要求具有高的能量分辨本领和探测灵敏度。常用于该种测量的是NaI闪烁探测器和HPGe探测器，而新的高压氙（HPxe）电离室探测器和LaCl3（Ce）探测器为核材料的鉴别提供了一种新的有效检测手段。     

惰性气体β-γ符合测量系统探测器能量及分辨率刻度

β-γ符合法是全面禁止核试验条约(CTBT)放射性核素核查中惰性气体氙测量的一种重要方法,探测器能量及分辨率刻度是其首要解决的关键技术。本工作详细介绍了β-γ符合测量系统NaI(Tl)闪烁体和塑料闪烁体探测器能量及分辨率刻度的方法和结果,采用γ放射性核素点源刻度NaI(Tl)γ射线能量及分辨率,利用137Cs661.66keVγ射线康普顿散射电子刻度塑料闪烁体β射线能量及分辨率,并与131Xem内转换电子刻度的β射线能量分辨率结果进行了比较。结果表明:用137Cs康普顿散射电子刻度塑料闪烁体β射线能量是一种简便可行的方法,但用其刻度的β射线分辨率比实际的大。     

Development of a direction finding gamma-ray detector

This paper describes a direction finding gamma-ray detector, which consists of three different scintillators; NaI (Tl), CsI (Tl) and BGO. The detector positively increases directional sensitivity to incident gamma-rays, and can measure direction, energy and number of gamma-rays. This detector will be useful to carry out monitoring of nuclear power plants or radiation facilities in emergencies. It will be also effective in searching for radiation sources such as radioisotopes and radioactive contaminations. Experimental results have shown the proposed directional detector has a potential for practical use in real fields and will contribute to radiation emergency preparedness.     

Fe-Doped High Purity GaAs as a Room Temperature Gamma-Ray Spectrometric Detector

Fe-doped high purity GaAs crystals have been grown using a vertical-type liquid-phase epitaxial technique and have been studied as room temperature gamma-ray spectrometric detectors for nuclear fuel safeguards. To improve the detector gamma-ray counting efficiency, a double-epitaxial-layer detector was studied.     

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.     

参考法扣除溴化镧探测器固有本底谱

为减少溴化镧[La Br3(Ce)]探测器固有放射性对低计数水平下测量的影响,探讨了一种参考法扣除La Br3(Ce)探测器固有本底谱。通过引入一个碘化钠[Na I(Tl)]探测器作为参考,并利用MC模拟得到两探测器的探测效率比,将屏蔽条件下La Br3(Ce)探测器能谱中的环境本底谱扣除,得到更准确的La Br3(Ce)探测器固有本底谱。实测能谱在扣除固有本底谱后,原本被固有本底谱影响的峰得到了恢复,有助于后续能谱分析中的定性和定量分析。     

GAGG:Ce探测器与NaI:TI探测器性能比较

研究了封装反射层材料对GAGG:Ce探测器光收集的影响,同时与Na I(TI)闪烁体探测器进行了详细的对比性实验,用137Cs、60Co标准源测量了γ能谱,对GAGG:Ce与Na I(TI)闪烁体探测器的温漂、能量线性及能量分辨率等性能指标重点进行了讨论。结果表明:GAGG:Ce探测器随温度漂移变化程度较大;能量线性好,线性相关度r为0.9999;对662 ke V的γ射线能量分辨率为7.8~8.0%。     

Positologica: A Positron ECT Device with a Continuously Rotating Detector Ring

A rotary positron emission computed tomography device is developed for human brain and animal studies. The device utilizes 64 rectangular BGO detectors arranged at unequal spacing on a circular ring. The detector ring is continuously rotated at a constant speed of 60 rpm or less. This single continuous motion of the ring with the detector array provides excellent sampling characteristics and high detector redundancy. The device has a field of view 24 cm in diameter with a slice thickness adjustable from 1 cm to 2 cm. Measured width of system response to a 2 mm diameter line source is 5.8 mm FWHM at the center and less than 9 mm FWHM within a circle 16 cm in diameter. Measured sensitivity including scattered coincidence events is about 17 kcps/pCi/ml for a 20 cm diameter water phantom and 2 cm thick slice.     

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.     

反应堆中子注量率相对分布测量系统铅屏蔽计算分析

为批量化测量探测片活性,设计了多道中子注量率相对分布测量系统。每一个NaI探测器测量一个探测片,探测器之间采用铅屏蔽。为了消除其他通道探测片对本通道探测片测量结果的影响,通过设计保证邻近通道活化探测片对本通道干扰小于0.05%。本文采用点源积分方法计算(经蒙特卡罗模拟验证),并确定了满足屏蔽要求的铅屏蔽体尺寸。     

脉冲中子全能谱测井闪烁探测器响应特性的蒙特卡罗模拟

利用蒙特卡罗方法模拟研究NaI和BGO晶体探测器对不同γ射线的响应。模拟结果表明,BGO晶体的光电峰和第一逃逸峰对计数贡献大,而NaI晶体的逃逸峰贡献大。对于井眼和地层流体分别为油和水砂岩地层,模拟改变NaI和BGO晶体探测器的直径和长度时的非弹性散射γ射线响应能谱,采用不同能窗处理方法对地层流体的分辨能力不同,选取光电峰和第一、第二逃逸峰对应的能量窗时,BGO晶体探测器比NaI晶体探测器测量的C/O（C与O的元素含量比）差值大,但受尺寸的影响不大;采用光电峰对应的能量窗时,BGO晶体探测器测量的C/O差值比NaI的大得多,且随尺寸的增加差值增大;能量道的漂移对C/O值影响较大,而能量分辨率对差值影响相对较小。     

Recent Advances in X-Ray Detection Technology

A review is presented of recent developments in x-ray photon detectors and in the associated detector electronics. The first portion of the paper is devoted to a survey of the presently available physical inforrnation on the "intrinsic" resolution of silicon and germanium radiation detectors, proportional counters and NaI(Tl) scintillation crystals. Semiconductor detectors suitable for x-ray applications and low noise electronics are then analyzed in some detail. Discussions follow on scintillation detectors, proportional counters, and "external" photoelectric detectors. Recent spectral achievements and interesting applications are illustrated.     

Development of a miniature gamma-ray endoscopic probe for tumorlocalization in nuclear medicine

Two types of miniature gamma-ray endoscopic probes developed for insertion into a body cavity to detect invisibly small or deeply located tumors are described. One is a single detector system using a small BGO (Bi₄Ge₃O₁₂) crystal connected with a fiber optic light guide, and the other is a dual detector system using a pair of single detector probes of the same size combined with a random coincidence technique. The performance of these detectors was tested by using a point source and a hollow cylindrical water phantom that simulated a body cavity. Measured and calculated results indicated that a dual detector system can be used for realistic tumor localization in a body cavity, and a single detector system may be applied only for the detection of tumors in which radiopharmaceuticals that emit gamma rays of energy below about 200 keV are accumulated     

脉冲中子全能谱测井数据处理方法及影响因素的模拟研究

C/O能谱测井是确定含油饱和度的主要测井方法,模拟水平井条件下的非弹性散射伽马能谱,研究C/O值与含水饱和度、孔隙度及泥浆侵入深度的关系。而探测器的类型、尺寸、探测效率、能量分辨率、稳谱、能谱的处理方法以及中子对探测器晶体的作用都会对测井结果产生影响。利用蒙特卡罗方法模拟源距分别为30cm和58cm处,且井眼和地层流体分别为油和水砂岩地层的中子能量分布,通过研究中子对NaI、BGO、GSO和LSO四种探测器的作用及响应关系得到：中子对探测器的作用将使地层流体分辨能力降低。模拟改变NaI和BGO晶体探测器的直径和长度时的探测器响应能谱,采用不同的能窗处理方法对地层流体的分辨能力不同,选取光电峰和第一、第二逃逸峰对应的能量窗时BGO晶体探测器测量的C/O差值要比NaI晶体探测器的大,但受尺寸的影响不大;但采用光电峰对应的能量窗时,BGO晶体探测器测量的C/O差值要比NaI大得多,且随着尺寸的增加差值也增加。能量道的飘移对C/O值影响较大,而能量分辨率对差值影响相对较小     

低本底反康普顿高纯锗γ谱仪

本文介绍的谱仪采用铅-石蜡-铅为主的复合物质屏蔽。HPGe探测器对~(60)Co的1332keV γ射线的相对效率为25％,能量分辨率好于1.75keV。在阱型反符合屏蔽下,系统对放在HPGe端面的~(137)Cs点状薄膜源的峰康比可达800:1;测量时间1000min,置信度95％时,对~(137)Cs点源探测灵敏度好于5.6mBq;谱议在100—2000keV能区内的积分本底好于8.7±0.1次/min,与无反符合屏蔽时相比,压缩倍数为6.6。