Optimization of the gamma-ray spectrometry counting time based on uncertainties of radionuclides concentration in samples

Marcelo Bessa Nisti,Fernanda Cavalcante,Catia Heloisa Rosignoli Saueia,Barbara Paci Mazzilli,Marcelo Francis Máduar

doi:10.15392/bjrs.v8i2.1197

Marcelo Bessa Nisti, Fernanda Cavalcante + Show 3 more

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https://doi.org/10.15392/bjrs.v8i2.1197

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Abstract

This paper aims to propose an easy and fast method of optimization of the gamma-ray spectrometry counting time in determining natural radionuclides (Pb-210, Pb-212, Pb-214, Bi-212, Bi-214 and Ac-228) in order to minimize uncertainties in the concentration. The samples were measured by gamma-ray spectrometry with a hyper-pure germanium detector Canberra, 25% relative efficiency, effective resolution of 1.9 keV on the 1332.5 keV 60Co with associated electronics and coupled to a microcomputer. Multichannel Maestro A65-I model was used for spectrum acquisition and peak net area determination, and WinnerGamma/Interwinner 6.01 software was used for gamma-ray spectra analysis and to calculate the concentrations and associated uncertainties. The counting times used were 86,000 s and 150,000 s.

Highlights

The technique of gamma-ray spectrometry is a powerful tool for determining the contents of gamma-ray emitter radionuclides in samples
An important step in using gamma-ray spectrometry on a routine basis for a given detection system is the definition of adequate counting time, which depends on the sample type, the radionuclides to be determined, radiation background, sample geometry and characteristics of the detection system
The natural radionuclides usually utilized in high resolution gamma-ray spectrometry for the determination of the 238U decay series are 210Pb, 214Pb and 214Bi, and for the 232Th decay series are

Summary

Introduction

The technique of gamma-ray spectrometry is a powerful tool for determining the contents of gamma-ray emitter radionuclides in samples. To ensure that high-quality spectra are obtained, good practices for their acquisition must be established, including physical setup, electronic settings, counting conditions, corrections for unwanted but inevitable sources of radiation [1] and validation by proficiency tests. An important step in using gamma-ray spectrometry on a routine basis for a given detection system is the definition of adequate counting time, which depends on the sample type, the radionuclides to be determined, radiation background, sample geometry and characteristics of the detection system (detector, shielding and associated electronics). Counting time in gamma-ray spectra acquisition can be preset relying in two criteria: the attainment of an acceptable minimum detectable activity (MDA) value; or instead the need to quantify the target radionuclide, even at very low concentration. A major issue in determining activity in samples with very low radionuclides concentration is the high uncertainties that arise, when not sufficient counting time is employed

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