Calibration and use of well-type germanium detectors for low-level gamma-ray spectrometry of sediments using a semi-empirical method

Abstract

Gamma-ray spectrometry is a widely used technique to quantify the presence of numerous radionuclides in environmental samples. In this work, we describe a methodology for efficiency calibration of four well-type germanium detectors and their use for the determination of low-level activities of gamma emitters in sediment samples. An experimental efficiency calibration for each detector was built with three materials for 17 energies, ranging from 46.5 keV to 1460 keV. For efficiency transfer to different geometries and sample types, we used the effective solid angle approach (ET-Ω method). Final calibrations were calculated for all detectors, several counting geometries, and elemental composition of selected sample types. Calibrations were validated with six reference materials. This methodology allowed to reliably analyze nine gamma emitters (²¹⁰Pb, ²⁴¹Am, ²³⁴Th, ²²⁸Ac, ²¹⁴Pb, ²⁰⁸Tl, ¹³⁷Cs, ¹³⁴Cs and ⁴⁰K) in sediment samples. Using these calibrations, gamma emitter profiles of sediment cores from contrasting aquatic systems (lake, intertidal, marine and deep-sea areas) provided reliable profiles of ²¹⁰Pb and artificial radionuclides useful for dating and stratigraphic interpretation. A protocol to implement this methodology is also presented.

Keywords: Efficiency calibration; Efficiency transfer; Environmental radioactivity; Gamma-ray spectrometry; Well-type detector.