Radial efficiency gradients in Ge(Li) gamma detectors

Counting of radioactive sources in contact with the vacuum container of a Ge(Li) detector may lead to errors because of large efficiency gradients. In order to explore the radial dimension of this problem, several point sources were stepped across in contact with the cap of several detectors, and curves of absolute efficiency against radius were measured. The insensitive core of an open-end coaxial detector reduced the central point-source efficiency at 122 keV at the cap to 20% less than a comparable closed-end detector. In compensation, however, there was a reduction in the radial efficiency gradient. The radial efficiency gradient was approximately proportional to the radius, with the central flattening for the open-end detector superimposed on the trend.     

Calculation of the absolute peak efficiency of Ge and Ge(Li) detectors for different counting geometries

A new method is presented to calculate with improved accuracy the absolute peak efficiency of cylindrical Ge and Ge(Li) detectors for point, disk and cylinder sources, positioned at any source-detector distance. Moreover attention was paid to true-coincidence effects. The method is extensively tested and applied for the analysis of reference materials. The accuracy turned out to be 3% or better. Research associate of the “Nationaal Fonds voor Wetenschappelijk Onderzoek”.     

Ge(Li) gamma-ray spectrometry as a pilot for NaI(Tl) gamma-ray spectrometry

Lithium-drifted germanium semiconductor detectors give much better resolution than do thallium-activated sodium iodide detectors, but much lower sensitivity. They can often advantageously be used in conjunction with NaI(Tl) detectors, to show whether corrections must be applied for activities other than the one to be measured and to provide the necessary information for calculation of the corrections.     

Total efficiency of gamma-ray detection by germanium semiconductor detectors

The total efficiency of γ-ray detection by Ge(Li) semiconductors is calculated for the energy range 0.1 to 10 MeV, for cylindrical detectors with radii from 0.25 cm to 2.5 cm and thicknesses from 0.1 cm to 1 cm, at distances between the source and detector ranging from 2 cm to 20 cm.     

A method for resolution enhancement of interfering peaks in Ge(Li) gamma-ray spectra

A method is proposed for the analysis of interfering peaks in Ge(Li) gamma-ray spectra making use of resolution enhancement by digital resonators. The successive steps of analysis are: (1) the resolution enhancement of multiplets by a special convolution transformation (5 or 7 channels); (2) non-recursive filtering and (3) the elimination of ripples. The final result of the first and second steps is equivalent of a digital resonator. A computional code is quite simple and can be executed by small computers. For opened multiplets one can obtain practically complete separation by means of this method. The limit of identification for a closed doublet of equal intensities amounts to about 0.6 times the FWHM. Subroutine COMPLEX was written in FORTAN IV and BASIC. The validity of the method is shown by an analysis of some synthetic multiplets and the determination of gold traces in Pt-Rh alloy by means of instrumental and destructive activation analysis.     

Use of the Pearson IV function to describe the dependence of detection efficiency of Ge detectors on gamma-ray energy

2000 analytical functions were fitted to the measured gamma-ray detection efficiencies of a Ge detector for a small irradiation vial located at the closest distance from the detector. Among these, the Pearson IV function, gave the best fit. The measured and calculated efficiencies were compared for 50 determinations (for energies which varied between 61 and 2754 keV) and a relative standard deviation of 8.3% was obtained.     

A least squares spectrum fitting method for the measurement of Ge(Li) gamma-ray peak areas

A method is described for the measurement of very small peak areas and for the resolution of multiplet peaks based upon least squares fitting procedures. The method does not use an analytical function to describe the peaks, but instead uses an actual peak shape derived from a γ-spectrum. Analysis of the IAEA. Intercomparison Spectra, G-1, is used to illustrate the technique.     

Spline and polynomial models of the efficiency function for Ge gamma-ray detectors in a wide energy range

Summary In one of our recent papers, the applicability of linear parameter functions for fitting the full-energy peak efficiency of n-type Ge gamma-ray detectors has been examined over a wide energy range of 50-8500 keV. In that paper we compared six different analytical functions and showed that higher-order polynomial functions on a log-log scale gave the best performance. However, there is a drawback to using the log-log scale when an additive function of efficiency at different energies or of the inverse efficiency has to be used in a fitting procedure. In the present study, the applicability of higher-order polynomial and spline functions to linear and inverse efficiency, but logarithmic energy scales, is examined.     

Efficiency calibration of Ge(Li) detectors,and the effects of geometry and physical properties of samples on the efficiency of detectors

To perform quantitative analysis of Ge(Li) spectra, not only energy calibration but also efficiency calibration procedures are done. Although the use of standard sample volume, mass, density and geometry is preferable, this optimum is not always possible. So to achieve an optimization is the main objective of the work reported here. Efficiencies have to be determined as a function of energy, density, thickness, mass of sample, intensity, and source-to-detector distance.     

Photoefficiency of gamma-radiation recording and limits of detection for individual elements in activation analysis using Ge(Li) semiconductor detectors

The photoefficiency and source utilization coefficients for 3.5, 28 and 45 cm³ Ge(Li) detectors were determined. Values of the source utilization coefficient were obtained as a function of the measurement geometry. Limits of detection were determined for 30 elements with long-lived isotopes and 38 elements with short-lived isotopes.     

The relative sensitivity and accuracy of NaI(Tl) and Ge(Li) detectors for minor components

A mixture of²³³Pa,¹⁴⁰La,⁸²Br,⁶⁴Cu.⁷²Ga,⁶⁰Co, and²⁴Na of known disintegration rates was counted on a NaI(Tl) and a large Ge(Li) detector. Both systems detected²³³Pa when present at 0.2%, and accurate results were observed for²³³Pa,¹⁴⁰La, and⁶⁰Co when present at greater than 0.5% of the total disintegration rate. The accuracy of the results from either system was not significantly different since the mean ratio of the observed to true results was 0.99±0.05 and 1.06±0.06, respectively. However, equal sensitivity and accuracy were achieved only when the counting interval for the germanium system was 1000 min, or 60 to 600 times that for sodium iodide.     

An anticoincidence-shielded Ge(Li) gamma-ray spectrometer and its application to radioanalytical chemistry problems

An anticoincidence-shielded Ge(Li) γ-ray spectrometer incorporating a largevolume, high-resolution coaxial diode inside a large plastic phosphor shield is described. It provides a peak-to-Compton ratio of 245: 1 for¹³⁷Cs and a significantly improved sensitivity for both low- and high-level radionuclide measurements. Examples of its application to neutron activation analysis, analysis of proton activated sources, and environmental radionuclide analysis are illustrated. This paper is based on work performed under United States Atomic Energy Commission Contract AT(45-1)—1830.     

A method for systematically analyzing Ge(Li) photopeaks

A relatively straight forward method of fitting Ge(Li) photopeaks with a Gaussian histogram is presented. The method, which is expecially suited to photopeaks which are distributed over a relatively small number of channels, determines photopeak area, pulse height, resolution and the residual background. Results are given to indicate the Gaussian distribution of the experimental data from −1σ to +6σ.     

Relative efficiency calibration of Ge(Li) detector in low energy region

The relative gamma-ray intensities in the energy region between 122 and 411 keV in the decay of¹⁵²Eu were measured by using a Ge(Li) detector. Its efficiency calibration was carried out with the radioactive sources of²⁴¹Am,⁵⁷Co,²⁰³Hg,¹³⁷Cs,¹³³Ba,⁷⁵Se,¹⁶⁹Yb and¹⁹²Ir.     

Some practical procedures in computerized thermal neutron activation analysis with Ge(Li) gamma-ray spectrometry

The practical use of a correction procedure for random coincidence losses, the determination of the detection limit and the standardization of measuring conditions are described. Special correction methods for the interference of the Cu analysis by²⁴Na, the burn-up of the radioactive nuclide formed and the interference of the Pt determination by Au are also given.     

Cross-correlation analysis of Ge(Li) spectra

A sensitive technique is proposed for activation analysis using cross-correlation and improved spectral orthogonality achieved through use of a rectangular zero area digital filter.     

A computer program for calculating Ge(Li) detector counting efficiencies for Marinelli beakers

A novel computing method has been developed to calculate the absolute photopeak efficiency of a Ge(Li) detector for Marinelli beakers of different heights and diameters and with variable density. For each point in the cylindrical sample the detection efficiency is calculated taking into account the distance from the detector and gamma-ray attenuation and the efficiency is integrated numerically over the volume of the sample. The detector is approximated as a point detector with an experimentally determined effective interaction depth. It is necessary to measure the absolute efficiency for a point source located on the detector axis and on a line beside the detector parallel to the axis. The computer program calculates the absolute counting efficiency for Marinelli beakers of any geometry and for any density. The measured and calculated values for three different densities give a good (–2.2%) overall agreement.     

Analysis of interfering peaks in Ge(Li) gamma-ray spectra using the resolution enhancement filters second version of the method

The new results obtained during the last two years are presented against a background of the previous development of the method (first version). The effect of the resolution enhancement filters containing non-recursive smoothing on the wide peaks, advantages of recursive technique and the construction of nonlinear baseline under multiplet to be resolved according to the GUNNINK and NIDAY method are reported in this paper.