A Coaxial Ge(Li) Gamma-Ray Spectrometer

A single-open-end coaxial type Ge(Li) γ-ray detector with an effective volume of 8.7cm³ and a capacitance of 35 pF was made by Li-drifting for 440 hr at an applied voltage of 140 V at 40°C in thermomodule-controlled constant-temperature water coolant. The FWHM energy resolution with an E810F preamplifier was 4.2 and 8.0 keV for γ-rays of 122 and 1,173 keV respectively. The pulse height distributions of γ-rays from an irradiated natural U sample and ¹⁰⁵Rh isotope were measured.     

Anticoincidence-Shielded Ge(Li) Gamma-Ray Spectrometer for Marine Environmental Radionuclide Analysis

An anti-Compton γ-ray spectrometer has been developed, which possesses a number of characteristics particularly adapted to direct measurement of low-level complex mixtures of radionuclides in marine environmental samples.

The detector assembly consists of a 42.7 cm³ coaxial Ge(Li) detector and a well-type 6″diam. × 4″ Nal(Tl) detector for the anticoincidence shield. The sample to be measured is placed on the Ge(Li) detector inside the well of the Nal(Tl) crystal.

Suppression of the Compton background is particularly marked at the Compton edge when the assembly is operated in anticoincidence mode. The anticoincidence shield reduces the ¹³⁷Cs Compton edge by a factor of 6.6 to provide a peak-to-Compton edge ratio of 210: 1 without reducing the full-energy peak efficiency by more than 2%. Similarly, for the 1,332.5 keV ⁶⁰Co γ-rays the Compton edge is reduced by a factor of 7 to give a peak-to-Compton ratio of 85:1, though in this case the peak efficiency is reduced by a factor of 1.8 due to the cascade decay.

This spectrometer has permitted the detection of a few pCi of fallout nuclides such as ¹³⁷Cs and ⁹⁵Zr, contained in 30 g environmental wet samples counted at intervals of 1,000 min.     

Environmental Gamma-Ray Exposure Rates Measured by In-Situ Ge(Li) Spectrometer

A conversion function (G(E) function) was determined to obtain an exposure rate directly from a γ-rays spectrum measured by an in-situ Ge(Li) spectrometer. In order to verify the utility of the G(E) function method, three kinds of detector, namely, a portable Ge(Li) detector, a Nal(Tl) detector and an ionization chamber, were used to measure exposure rate due to environmental γ-rays at the same place, and the measured values of exposure rate were compared with each other. Two exposure rate values were obtained from a γ-ray spectrum measured by the Ge(Li) detector, using two different methods, namely, the G(E) function method and the HASL method. The average of exposure rates obtained by four different methods was 4.15 üR/h, and the deviation was 15% of the average.

By applying both the G(E) function method and the HASL method to an environmental γ-ray spectrum, a total exposure rate can be determined directly without information on the distribution of the radionuclides in soil, and individual exposure rates due to ⁴⁰K, ²³⁸U and ²³²Th series and ¹³⁷Cs of the known distribution in soil can be also determined.     

Timing Characteristics of Large Coaxial Ge(Li) Detectors for Coincidence Experiments

The high efficiencies of large volume 'coaxial' Ge(Li) detectors make them attractive for coincidence experiments. However the electric field in this configuration is not uniform and hence the charge collection times vary widely as a function of position in the detector. The resultant variations in output pulse shape limit coincidence resolving times. In our studies one 511 keV annihilation quantum (22Na source) was detected in a scintillation counter to establish the zero (start) time and its partner in the Ge(Li) detector (at 1500 V) was accepted only when a full energy pulse was registered. The stop pulse to the timesorter was generated by the leading edge of the Ge(Li) preamplifier pulse at ~ 10% (50 keV) of maximum amplitude. Scanning the detector with a 1 mm wide collimated ?-beam resulted in time distributions whose full widths at half-maximum (fwhm) were ~ 8 nsec in the coaxial region of the detector broadening to ~ 35 nsec at the closed end. The distributions are skew in shape with long approximately exponential tails having half value slopes of ~ 5 to ~ 20 nsec. Similar studies with stop pulses generated at ~ 50% of maximum amplitude show much broader time distributions. The position variation in pulse shapes due to charge collection time was confirmed from oscilloscope photographs by triggering with the scintillation counter 'start' pulse.     

In-Situ Measurement of Fission Product Plateout in In-Pile Gas Loop Using Portable Ge(Li) Gamma-Ray Spectrometer

A nondestructive and quantitative method of measuring fission products deposited on inside surface of the primary duct has been developed. A portable Ge(Li) detector with a lead collimator was used for the external scanning of γ-rays emitted from the fission product plateout in the duct.

Upon termination of the first irradiation cycle for the coated particle fuels in the high temperature in-pile gas loop OGL-1 installed in JMTR (Japan Material Testing Reactor), in-situ measurements of the plateout were carried out by the above method at different points in the primary system.

Identified nuclides in the measured γ-ray spectra were ¹³¹I, ¹³³I, ⁹⁵Zr, ⁹⁵Nb, ¹³⁷Cs, ^110mAg, ⁹⁹Mo, ¹⁴⁰La, ⁶⁰Co, ⁵⁸Co, ⁵⁴Mn, ⁵¹Cr, ⁶⁵Zn, ⁵⁹Fe, ¹²²Sb, ¹²⁴Sb, ¹⁸²Ta, ¹⁸¹Hf, ²²Na and ⁴⁶Sc. The plateout densities of these nuclides were obtained using conversion coefficients determined by detector calibration and calculation, which were from 10^-5 to 10^-2 μCi/cm².

It was shown clearly by the experiment that the present measuring method using an in-situ γ-ray spectrometer is useful in the studies of fission product plateout in the primary cooling system of a high temperature gas cooled reactor.     

On the Origin of Leakage Current in Ge(Li) Gamma-Ray Detectors

Hole-electron pair generation in Ge(Li) ?-ray detectors due to thermal radiation from the cryostat outer casing is suggested as an often overlooked source of detector leakage current. Thermal-radiation-induced currents of the order of 10-9A are estimated for a typical large coaxial detector at 77°K when the cryostat outer casing is at 300°K.     

Active Sample Anticoincidence Guarded Ge(Li) Spectrometer for Low Level Radionuclide Analysis

The problem of spectral interference in large volume radioactive samples counted in a guarded Ge(Li) spectrometer is attacked by a new approach. By making the sample itself a liquid scintillator detector, and using coincidence and anticoincidence gating, the detrimental effects of self absorption can be eliminated. In addition, this technique (denoted gamma-beta coincidence and gamma-beta anticoincidence spectrum analysis) allows discrimination between modes of decay. The system design, logic, performance, and significance to low level radionuclide analysis is presented.     

Variation of Intensity of Environmental Gamma-Rays Measured with Ge(Li) Spectrometer

The variation of the intensity of environmental γ-rays has been studied with a Ge(Li) spectrometer. The 12 γ-rays were selected to be examined and typical characteristics of variations were obtained for each γ-rays. The intensity of γ-rays of ²¹⁴Pb and ²¹¹Bi which are ²²²Rn daughter nuclei increases on rainy days to the severalfold value of the average in the case of no precipitation. These variations were observed to be roughly proportional to rainfall rate in a sequence of precipitation. The γ-rays intensity of nuclides of the thorium series and ¹³⁷Cs is nearly constant within about 3% regardless of the weather. Its variation is about equal to the statistical fluctuation of the present measurements. The mean diurnal variations of f-ray intensity were obtained on days without precipitation. The intensity of ²¹⁴Pb and ²¹⁴Bi j-rays fluctuates nearly sinusoidally with an amplitude of about 6% of the average value and the maximum in the early morning.     

Further Charge Collection Studies in Coaxial Ge(Li) Detectors

Calculations have shown that, for comparable trapping lifetimes, the effect of charge trapping in a coaxial detector is significantly less for the carriers which move radially outward from the core than for those which move inward, as a consequence of the non-uniform electric field. This has been verified by resolution measurements on two thin coaxial detectors made from the same hole-trapping crystal; one was made conventionally, by drifting lithium in from the outer surface, the other in an "inside out" configuration by drifting lithium outward from the surface of a central hole.     

NaI(Tl)γ谱仪测量数据的计算机处理方法

本文介绍了使用NaI(T1)γ谱线在铅室内分析环境土壤样品和就地γ辐射谱测量的刻度方法,以及专用微机解谱程序的功能和使用方法。     

Ge（Li）探测器的体源峰效率刻度

本文介绍了用点源模拟法来刻度体源峰效率的方法和刻度结果,并与直接体源法相比较,误差约为5％。     

Timing Performance of Ge(Li) Detectors

The influence of several parameters related to the detector,. such as depletion layer thickness, external radius of coaxial counters, applied electric field on the timing properties of planar and two open ended coaxial Ge(Li) detectors is investigated. Besides, the role of the electronical conditions is studied.     

Si（Li）电子谱仪的研制

研制了“无窗”的Ｓｉ（Ｌｉ）电子谱仪，测量了＾２０７Ｂｉ的内转换电子能谱，对能量９７５．６２ｋｅＶ的电子取得了２．０７ｋｅＶ的能量分辨率。     

塑料闪烁体环探测器作反符合屏蔽的NaI(Tl)γ能谱仪

本文报告了一个用塑料闪烁体环探测器作反符合屏蔽的NaI(T_1)γ能谱仪的结构及主要性能。它采用Φ76×76mmNaI(Tl)晶体作为主探测器和符合探测器,以自制的Φ500×520mm塑料闪烁体作环探测器。在有无井型反符合屏蔽条件下,能量范围0.1—2MeV时,谱仪的积分本底比为2.8,对~(137)Csγ源的康普顿减弱因子(积分比)为2.5。当源位于晶体表面中心时,谱仪对~(137)Cs源的能量分辨率和全能峰效率分别为9.5％和8.4％。     

Components of the background of Ge(Li) and Ge detectors in passive shielding

The components of the background of a Ge(Li) detector and an ultrapure Ge detector in gamma spectrometers in passive shielding with a special design were studied in a ground-surface laboratory in 1996–2006. The measurement time varied from 45 to 240 h. The background for the detectors is due to radionuclides in the shielding material and cavities in the shielding and the detector materials themselves. Special attention is devoted to the study of the time dependence found for the background of the daughter of products of ²²²Rn decay, including the 46.5 keV peak of ²¹⁰Pb. __________ Translated from Atomnaya énergiya, Vol. 103, No. 5, pp. 318–322, November, 2007.     

第三代电子动量谱仪的多参数符合测量系统研制

本文介绍了一种新研制的用于第３代电子动量谱仪的多参数符合测量系统。该系统以６个慢符合道的电荷脉冲信号（它含有位置信息）和一个快符合道中的符合时间信号作为７个参数，采用７个数据获到通道并行获取数据，经计算机系统处理，可同时得到（ｅ，２ｅ）反应相关的符合多道时间谱，电离能谱和电子动量谱。