Brigitte R. S. Pecequilo
Cidade Universitária, Brazil
Title: Self-attenuation factors in gamma-ray spectrometry
Biography
Biography: Brigitte R. S. Pecequilo
Abstract
Gamma-ray spectrometry with high-resolution semiconductor detectors is currently the most widely used analytical technique for qualitative and quantitative determination of gamma-ray emmitters radionuclides. Quantification of elements relies on the correct analysys of the spectra, depending strongly on the efficiency calibration of the measurement apparatus, most often performed with aqueous standard multi-radionuclides solutions. Soever, lower energy gamma rays have less penetrating ability and tend to interact more readily with matter, so, when the efficiency calibration curve is obtained with an aqueous standard multi-radionuclides solution, a self- attenuation correction is required if samples present densities higher than the water ones. Samples such sand, soils and sediments have apparent typical densities varying from 1.2 g.cm-³ to 2.9 g.cm-³, so a correction of the efficiency curve is necessary. Self-attenuation factors are determined by Cutshall transmission technique, measuring the transmission of gamma rays through both the solid sample and an ultrapure water sample in the same geometry, using punctual sources, with gamma transitions in the range of interest. All samples are measured in the same geometry with high-resolution HPGe detectors. Self-attenuation correction factors are experimentally determined for every different sample density. A study of two hundred samples of sands and soils, allow to conclude that, to obtain more reliable analyses, one should use correction factors for the self attenuation behavior, especially in the lower part of the energy spectrum. Also, as attenuation, apart from density, strongly depends on the sample chemical composition, correction factors must be determined for each studied sample.