Coincidence summing in gamma and X-ray spectrometry

doi:10.1016/0168-9002(93)90394-W

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Volume 325, Issue 3, 15 February 1993, Pages 478-484

https://doi.org/10.1016/0168-9002(93)90394-W Get rights and content

Abstract

A new technique to calculate coincidence-summing corrections in γ-ray spectroscopy developed by Semkow et al. [Nucl. Instr. and Meth. A290 (1990) 437] was extended to incorporate coincidence-summing effects due to X-rays. The technique was experimentally validated in the case of ¹³⁹Ce measurement. It is shown how the technique can be applied for the calculation of the full-energy peak and of total detection efficiencies. In addition, an absolute method for measuring the activity of a point source is proposed and demonstrated in the case of ¹³⁹Ce. Finally it is shown how this improved technique can be applied to assess the ratios of the probabilities for emission of X-rays and for parameter optimization in peak-evaluating procedures.

References (7)

T.M. Semkow et al.
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There are more references available in the full text version of this article.

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A code is developed to correct for the coincidence summing effect in detecting a voluminous gamma source, and this code is applied to a¹⁵²Eu standard source as a test case. The source is 1000 mL of liquid in a cylindrical shape. To calculate the coincidence summing effect, the cylindrical source is considered as 10(radial) × 8(height) sectional sources. For each sectional source, the peak efficiency and total efficiency are obtained by Monte Carlo simulation at each energy for 10 energies between 50 keV and 2000 keV. The efficiencies of each sector are then expressed as polynomials of gamma energy. To calculate the correction coefficients for the coincidence summing effect, the KORSUM code is used after modification. The magnitudes of correction are 4%–17% for the standard ¹⁵²Eu source measured in this study. The relative deviation of 4.7% before the coincidence correction is reduced to 0.8% after the correction is applied to the efficiency based on the measured gamma line. Hence, this study has shown that a new method has been developed that is applicable for correcting the coincidence effect in a voluminous source, and the method is applied to the measured data of a standard ¹⁵²Eu cylinder source.
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The chapter provides a description of inorganic crystal scintillators, their properties, and the mechanisms of scintillation in inorganic crystals. This includes a description of the various components of the solid scintillation analyzer, the crystal detector, photomultipliers, pulse height discriminators, single- and multichannel analyzers. Concepts and principles of solid scintillation analysis are described, including gamma-ray spectra, counting and detection efficiencies, activity determinations, self-absorption, counting geometry, spectral resolution, and background measurements. Automated methods of solid scintillation analysis included automated gamma analysis and microplate scintillation techniques. A treatment of the scintillation process in plastic media and the applications of plastic scintillators are included. The chapter provides a treatment on the measurement of neutrons with inorganic scintillators, and neutron detectors with scintillating and optical fiber. Neutron/gamma pulse shape discrimination and Bonner sphere neutron spectrometry are described in discussions on the measurement of neutrons with solid scintillators. Principles and practice in the application of the Lucas cell for the measurement of ²²²Rn are included. Advances in the development of phoswich detectors are described for the simultaneous detection and measurement of alpha-, beta-, gamma-rays and neutrons, low-level counters, the simultaneous measurement of neutron/gamma/proton fields, and simultaneous beta- and gamma-spectroscopy. Other applications of inorganic crystal scintillators described include neutrino detectors, the detection and measurement of double beta (ββ) decay, and the use of scintillation detectors and scintillating bolometers in the search for neutrinoless double beta (0νββ) decay and the search for weakly interacting massive particles.
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A trapezoid approach for the experimental total-to-peak efficiency curve used in the determination of true coincidence summing correction factors in a HPGe detector
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Citation Excerpt :
For example, ignoring TCS effects can lead to a typical error with a factor of 2 in the determination of 60Co activity when a well-type Ge detector is used (Laborie et al., 2000). In literature, the problem of true coincidence has been investigated for both point and voluminous sources by many researchers (Andreev et al., 1973; Debertin and Helmer 1988; Moens et al., 1982; Korun and Martincic 1993; Kolotov et al., 1996; Sima, 2000; Korun, 2001; Blaauw and Gelsema 2003; Vidmar and Korun 2006; Arnold and Sima 2006; Vidmar et al., 2007). A method was developed to characterize a well-type detector with using a full-energy peak (FEP) and a peak-to-total (PTT) efficiency curves that were determined using coincident photons from a nuclide by Blaauw who used a two-parameter function to describe the energy dependence of PTT ratio and extended it to volume sources (Blaauw, 1998).
In this work, a simple method for true coincidence correction is suggested for a voluminous source measured in close detection geometry for a HPGe detector. TrueCoinc program based on Sudár's algorithm was used to determine true coincidence summing correction (TCS) factors by using full energy peak (FEP) efficiency, and total-to-peak (TTP) efficiency curves in which experimental efficiencies are obtained from almost coincident-free radionuclides such as ⁵⁴Mn, ⁵⁷Co, ⁶⁵Zn, ¹⁰⁹Cd, ¹³⁷Cs and ²⁴¹Am. In order to calculate TTP efficiency curve three different approaches were tested. One of them is new and here called trapezoid approach which was used successfully in determining total count of spectrum for the TTP efficiency curves. According to different TTP determination methods, the changes in true coincidence factors are observed. The FEP efficiency curves are also established for a cylindrical source. Then, TCS factors were determined for the particular peaks of daughters of ²²⁶Ra, ²³⁸U, and ²³²Th using the suggested method. Those activities measured from some certified reference materials such as IAEA RGU-1 and RGTh-1 are used to validate the present TCS correction procedure.
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2012, Applied Radiation and Isotopes
Citation Excerpt :
For n-type detectors other challenges arise; the low energy 14 keV gamma photon of 57Co contributes to summing-out of the 122 keV peak and summing-in to the 136 keV peak, and coincidence summing between gammas and x-rays, as it occurs for 88Y and 139Ce, becomes significant. Although corrections for some of these cases have been described earlier (Korun and Martincic, 1993; Novkovic et al., 2007), this technical note presents simplified methods to correct for summing effects in 57Co, as well as for summing of gammas with x-rays having energies up to 40 keV for n-type HPGe detectors. Three lead-shielded coaxial HPGe detectors were used for this project: a 50% relative-efficiency n-type detector with a carbon fiber window (denoted G7), a 33% n-type detector with a beryllium window (G3), and a 44% p-type detector (G6) serving as a control.
Simple and practical coincidence summing corrections for n-type HPGe detectors are presented for the common calibration nuclides ⁵⁷Co and ⁶⁰Co using a defined “virtual peak” and accounting for the summing of gamma photons with x-rays having energies up to 40 keV (⁸⁸Y and ¹³⁹Ce). These corrections make it possible to easily and effectively establish peak and total efficiency curves suitable for subsequent summing corrections in routine gamma spectrometry analyses. Experimental verification of the methods shows excellent agreement for measurements of different reference solutions.

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