Ge Detector System Research Articles

Precision measurements of gamma-ray intensities I. 56Co, 88Y, 110mAg, 134Cs and 207Bi

To determine relative intensities of gamma rays in the region of 280–2750 keV, Ge(Li) detectors were calibrated with eight kinds of standard sources and four kinds of cascade gamma-ray sources. The disintegration rates of the standard sources were determined by means of the coincidence method. Intensity measurements were performed with two Ge(Li) detector systems. Experimental conditions were improved, especially for source positions and the dead time. The total number of calibration measurements was 437. Gamma-ray spectra were carefully analyzed, and the sum effect was corrected. Relative gamma-ray intensities of 56Co, 88Y, 110mAg, 134Cs and 207Bi were obtained with errors less than 0.5% for strong gamma rays.

Irradiation history of the Kirin meteorite.

Cosmogenic nuclides have been studied in the Kirin chondrite (H5). Some experimental results obtained in samples sent to us (Nos. 1 and 4 fragments) are described. We measured the gamma rays of 50Mn, 26Al, 22Na and 60Co, using Ge(Li) detector systems. 53Mn was determine by an activation method based on 53Mn(n, γ)54Mn. The light rare gases were also measured by a mass spectrometer in one of the specimens. We compare our data with others and conclude that it is possible to read out the fossil records in the meteorite and interpret them by, 1) Multiple exposure history and 2) Depth effects in the production of cosmogenic nuclides in different geometries.

Nuclear magnetic moment of the 161 keV state and other spectroscopic investigations of 133Cs

The magnetic moment of the 161 keV state of 133 Cs was remeasured by the 1PAC technique in an external magnetic field of 9.5 T as μ I(161keV) = 2.0(2)n.m. The known half-life of the 161 keV state, T 1/2 = 190(15)ps, was confirmed by a Coulomb-excitation experiment. The 161 keV state as well as the few other states for which large B(E2)↑ values are observed exhibit the characteristic properties of a ground state core-excitation multiplet as proposed by de-Shalit. A high precision remeasurement of the 276 keV–161 keV γ-γ angular correlation by use of a three Ge(Li) detector system gave A 2 = −0.495(5) and A 4 = −0.54(6), and confirms the result obtained by Winn and Sarantites which is in contradiction to all previous data. A comparison of the M1/E2 mixing ratio derived from this angular correlation for the 161 keV transition with recent precise data for the total conversion coefficient proves that anomalous conversion is present and leads to the penetration parameter λ = +25(9).

An anticoincidence-shielded Ge(Li) gamma-ray spectrometer with high sensitivity for measurement of environmental radionuclides

This paper describes a Ge(Li) detector system with anticoincidence shield designed for gamma-ray spectrometry of environmental samples. The system embodies three main differences from some previous designs. First, to minimise cost, a Ge(Li) detector made of standard materials was used. Second, the sample chamber is located in the anticoincidence shield so as to afford, depending upon source geometry, a greater efficiency for lower energy Compton scattered photons. Third, and more importantly for good sensitivity, a large sample may be accommodated in a re-entrant chamber. The system is based on a closed-end coaxial Ge(Li) detector of 75 cm3 volume with 2.0 keV fwhm resolution at 1332 keV. The anticoincidence shield consists of two cylinders of NE110 plastic scintillator each of 30 cm radius and 30 cm long. Calculations were carried out to determine for a small source the best position of the sample chamber to achieve, with acceptable sacrifice, improved Compton suppression at lower energies (100–200 keV) where backgrounds usually pile up but in which region there may be peaks of interest. Good agreement was obtained between expected and achieved suppression at different energies using a small 137Cs source. Background spectra under different shielding conditions are discussed, and the system's usefulness is illustrated using the spectrum produced by nuclear weapon test fallout on an air filter. Examples are given of calibration of the system using sources prepared from reference solutions. As an illustration of the sensitivity of the system, minimum detectable activities for two types of sample are calculated. Experience in operation verifies these results. In a bulk sample, an activity concentration of 12 fCi/g of 137Cs is measurable with an accuracy of ±10% (one standard deviation) in 1000 min. This performance is at least comparable with other more elaborate systems.

Evaluation of Well-Type Ge(Li) Detectors for Low-Level Radiochemical Analysis

Well-type Ge(Li) detectors have been evaluated for low-level gamma-ray spectrometry and radiochemical analyses. The detectors were found to have good resolution, high peak-to-Compton ratios and low backgrounds. The use of an anticoincidence shield further improves the detector performance. The detector efficiencies and backgrounds are compared with those obtained with other Ge(Li) detector systems. The well detectors were found to have better detection efficiencies and as low backgrounds as either large coaxial detectors or opposed detector systems. Sum-coincidence effects are more pronounced in the well detector and use of this feature is discussed. Applications which utilize the low-energy response of the detector are described. Minimum detectable activity levels were determined for several nuclides.

Doppler Broadening Measurement of Positron Annihilation in Alkali Halides

Doppler broadening method of positron annihilation (DOBPA method) is developed, and applied to the study of electronic structures of alkali halides. Radiation from positron annihilation in 14 kinds of alkali halide single crystals were measured with a Ge(Li) detector system. Observed Doppler broadened spectra were unfolded by computer, and intrinsic distributions were obtained. Electron momentum distributions were extracted from these distributions. To study anisotropy of the momentum distribution, radiation was measured along the [110] direction as well as along the [100] direction. Anisotropy of the momentum distribution was observed except for lithium halides and cesium halides. The strongest anisotropy was found in RbBr.

Total toK-shell photoelectric cross section ratios in Zr, Ag, Ta, and Th

Total photon atomic cross sections in elements Zr, Ag, Ta and Th were determined around theirK-edges in the energy region 6 to 400 keV with a good geometry set-up using proportional counter or Ge(Li) detector system. From these values the photoelectric cross sections were obtained by subtracting the theoretical values of coherent and incoherent scattering cross sections. The resulting photoelectric cross sections were fitted to curves above and below theK-edge for each element and extrapolated on either side and the total toK-shell photoelectric cross section ratios were determined with an error not exceeding 2%. The ratios were compared with the theoretical values obtained by Grodstein and others, as also from the empirical relation of Hubbell. The present values show good agreement with those of Scofield. A definite trend of decrease of the ratio as the energy increases is observed in the case of Th unlike in the previous experimental studies.

Total photon cross-sections in the energy region (5÷1100) keV

Total photon cross-sections are measured by using the transmission method in a good geometry set-up in elements 6≤Z≤92 at twenty-one energies in the region (5÷1100) keV by means of proportional counters and a Ge(Li) detector system. The measured cross-sections are compared with the theoretical predictions of Scofield and Storm and Israel. The values in general agree within 1%.

The K-conversion coefficients of γ-rays above 800 keV from 182Ta decay

The relative intensities of the K-shell internal conversion electrons above 800 keV from the decay of 182Ta(115 d) have been studied. These measurements were made with a π√2 iron-free, magnetic, electron spectrometer with observed resolutions of 0.075 to 0.20%. Relative γ-ray intensities were also determined on Ge(Li) detector systems. These data were combined to obtain K-shell conversion coefficients for 21 transitions. The estimated uncertainties are as small as 0.5% for the relative electron intensities and 0.8% for the conversion coefficients. Multipole mixing ratios are determined for a number of the transitions.

Sodium In-Pile Loop Experiment on Delayed Neutron Detector-, Precipitator-, and Cover-Gas Gamma-Ray Spectrometer-Type Fuel Failure Detection Systems

Performance of four different types of fuel failure detection systems has been studied using a sodium in-pile loop located in Japan Research Reactor No. 2. In the sodium in-pile loop, 8.5 liter sodium circulates through an irradiation section (500°C), a main cooler (400°C), an expansion tank (380°C), an electromagnetic pump, and a main heater at a flow rate of 3 liters/min. In the irradiation section, four metallic uranium (20% enriched) plates of a total amount of U-235 of 9.18g had been irradiated at a thermal neutron flux of 5.4×1010 n/cm2sec. A delayed neutron detector consisting of a BF3 counter system in a graphite moderator (50cm×5Ocm×8Ocm) detects delayed neutrons from fission products in the expansion tank. Helium cover gas over the sodium in the expansion tank carries gaseous fission products to a precipitator (The Plessey Co. Ltd., Mark XI) by which beta-rays from Rb-88 and Cs-138 collected on the precipitator wire are detected. The precipitator was modified to measure gamma-ray spectra from the wire using a Ge(Li) detector system for the nuclide identification. The helium gas is also guided into a gas reservoir whose gamma-ray spectra are analysed by another Ge(Li) detector system. Construction and performance of these detection systems was described in detail and their detection sensitivities and response were compared.

Spin values of the low lying nuclear levels of201Hg

Gamma-gamma directional correlations have been investigated for the cascades of 135-30 keV and 135-32 keV in201Hg from the decay of201Tl. A combination of NaI (Tl) and Si (Li) detectors was used for the experiments. Spin values ofI=1/2, 3/2 and 1/2 have been assigned to 1.58, 32.19 and 167.49 keV energy levels. In addition, the relative intensities of theγ rays have been measured with a Ge (Li) detector system. The results are 2.2±0.2, 2.2±0.2, 26.5±1.3, 1.6±0.1 and 100 for theγ rays of 30.60, 32.19, 135.34, 165.88 and 167.43 keV energies, respectively.

Low-background Ge(Li) detector systems for radioenvironmental studies

Two Ge(Li) detector systems designed to measure low-level radioenvironmental samples are described. The materials used in the construction of these systems and the effect of these materials on the background radioactivities are discussed. One system, designed to count mid-range specific activities, contains a closed, coaxial, 10% Ge(Li) detector that is housed in electrolytic magnesium and operated within a standard lead cave. Continuum background levels in this system vary from 0.1 c/min keV at 200 keV to 0.01 c/min keV at 1 MeV. The second system, designed for maximum sensitivity, contains a 15%-relative-efficiency Ge(Li) detector housed in electrolytic magnesium and operated in anticoincidence with a large plastic detector. This entire system is placed inside a lead-and steel armor plate shield located in a counting room below ground level. For single gamma-ray emitters from point sources, the maximum continuum suppression factor is greater than 8. Under suppression conditions the background continuum, as well as the usual contaminant peaks, are the lowest yet reported for Ge(Li) environmental counting systems. Continuum values decrease from about 6 × 10 −3 c/min keV at 200 keV to less than 3 × 10 −4 c/min keV at 1 MeV. A 1000 min count of 250 g of soil shows that this system can measure a 137Cs specific activity of 20 fCi/g with a precision of 15%. The lowest specific activity per gram detectable in a one-week count under threshold conditions (± 50%) for a single gamma-ray emitter with E γ >500 keV is several hundred aCi/g.

Comparison of Ge(Li) and Anti-Compton Systems for Measurements of Environmental Samples

There are numerous reasons for performing environmental measurements for routine health or safety monitoring and to determine the movement of trace elements or radionuclides through our environment to man. This is often a requirement for the licensing of nuclear power reactors, as well as many other meteorological or environmental research experiments. In this paper a variety of sensitive low-level counting systems have been discussed from an analyst's viewpoint, centering on a variety of NaI(Tl) and Ge(Li) gamma ray spectrometers. The coincident gamma-ray emitters are most sensitively detected through NaI(Tl) multidimensional gamma ray spectrometry, while single gamma ray emitters are very sensitively detected with Ge(Li) detector systems. NaI(Tl) detector systems are superior in general for environmental measurements.

In situ activation analysis of marine sediments with252Cf

A seabed nuclear probe has been developed which permits the measurement of up to 33 elements at the parts per thousand to parts per million levels in continental shelf areas. The probe consists of a neutron irradiation source,252Cf, which neutron activates the elements in the minerals of interest. These resulting radioactive elements emit characteristic gamma radiation which is analyzed in situ in 2- to 10 min counting intervals with a Ge(Li) detector system. Details of the irradiation source, the Ge(Li) detector, and spectra taken in situ in a marine environment are discussed with respect to the detection of the minerals at concentrations of economic interest.

Trace element distributions in man-made fibers

A preliminary study to evaluate the use of neutron activation analysis for the characterization of six groups of man-made fibers for forensic purposes has been made. A total of 81 samples of acetate, acrylic, modacrylic, nylon, polyester and rayon were analyzed. Small samples, approximately the size typically found during a crime scene search, were analyzed using a Ge(Li) detector system following a 20 min irradiation at a flux of 5·1013 n·cm−2·sec−1. The following elements were determined quantitatively in one or more of the samples: Ti, Sr, Au, Zn, Sb, Br. Mn, Mg, Cu, In, Co, Cu, V, K, Al, Cl, Na, Ca, and S. Significant qualitative and quantitative differences were found both between and within the six groups. However, within certain groups some fibers from different manufacturers showed marked similarities in qualitative and quantitative composition.

A High-Rate Direct-Coupled Preamplifier for High Energy Ge Detector Systems

The fast counting of high energy gamma events with excellent resolution is made possible by the design of a recycling preamplifier and a direct-coupled spectrometer system. Measurements were performed with a 40 cc Ge(Li) coaxial detector. Data were observed with and without pile-up rejection for count rates up to 150,000 counts/s. Resolution without pile-up rejection for 60Co was 2.50 keV FWHM at 75,000 counts/s (1.5-μs shaping). The exceptional performance of this direct-coupled system is mainly attributed to the preamplifier which requires no pole-zero compensation. After single differentiation the pulses return precisely to the baseline.

The HASL Ge(Li)-NaI(Tl) Low Level Counting System

A high efficiency Ge(Li) detector system with a NaI(Tl) annulus and back-detector has been developed to provide coincident and anti-coincident gamma-ray spectrometry of low level samples. Independent control of the three detector signals and a flexible logic arrangement allow optimum detection of non-coincident (Compton suppression) or coincident gamma-rays with either wide or narrow angles of correlation. This counting system and its application to the analysis of environmental samples is described.

Decay of naturally occurring 138La

Abstract The decay of naturally occurring 138La was investigated using a Ge(Li) detector system. In addition to the 33 keV X-ray, the energies of the two γ-radiations emitted were measured to be 1.436 ± 0.001 MeV and 0.788 ± 0.001 MeV. The partial half-lives of the EC branch to 138Ba and of the β-decay branch to 138Ce were calculated from intensity measurements to be (2.34 ±0.37) × 1011 and (4.7 ± 1.5) × 1011 y respectively.

Gamma-gamma directional correlations in 140Ce

Abstract Directional correlation measurements have been performed on six γ-ray pairs occurring in the de-excitation of 140 Ce. Of these, two are 1–3 correlations with an unobserved intermediate γ-ray. Both NaI(T1)-Ge(Li) and Ge(Li)-Ge(Li) detector systems were used. The following mixing ratios were deduced for the 329, 433, 487, 752, 816 and 868 keV transitions: δ (329; D , Q ) = 0.018±0.007, δ (433; D , Q ) = 0.36 ±0.02 or −0.14±0.03, δ (487; Q , O ) = −0.002±0.007, δ (752; D , Q ) = −0.33 ±0.03, δ (816; D , Q ) = 0.031±0.005, −0.09 δ (868; D , Q )

810.6?863.6 keV ??-directional correlation in58Fe

The 810.6–863.6 keV γγ-directional correlation has been measured with an NaI(Tl)-Ge(Li) detector system. The NaI window was set on the 810.6+863.6 keV composite peak. From the (810.6 NaI gate) (863.6 Ge spectrum) data at 90 °, 135 °, and 180 °, we deducedA2=+0.51±0.03 andA4=+0.09±0.04. These results disagree with the values previously obtained from58Co decay (with Nal-NaI detector systems) but agree with the values from γγ(θ) studies following thermal neutron capture by57Fe.