Determination of 226Ra and 238U in environmental samples from the analysis of the 186 keV photopeak and their progeny in equilibrium.

Abstract

Radium-226 is a significant natural radionuclide in environmental studies, primarily due to its decay product ²²²Rn and its progeny. It is widely determined via the short-lived ²²²Rn progeny in equilibrium, a well-established method. Alternatively, ²²⁶Ra can be quantified through its 186.21 keV γ-ray. In environmental samples, this photopeak overlaps with the 185.72 keV peak of ²³⁵U, forming a multiplet around 186 keV, which is challenging to deconvolute. Resolving these peaks provides valuable information for the determination of ²²⁶Ra, ²³⁵U and ²³⁸U. At Nuclear Engineering Laboratory of the National Technical University of Athens (NEL-NTUA), both the direct and indirect methods for analysing ²²⁶Ra, ²³⁵U, ²³⁸U as well as other natural radionuclides such as ²¹⁰Pb, ²²⁸Ra and ²²⁴Ra in environmental samples have been employed for decades. For the γ-spectroscopic analysis at NEL-NTUA, the in-house developed SPUNAL code is used, which however does not always analyse the multiplet photopeak at ∼186 keV to its components. This study introduces an enhancement of the methods applied, combining a new calibration of the detector system and a suitable algorithm to resolve the multiplet peak at ∼186 keV. The method offers results from both the 186 keV photopeak analysis and the γ-rays emitted by ²³⁴Th and the short-lived radon progeny, ensuring the accuracy of yielded results for ²²⁶Ra, ²³⁵U and ²³⁸U. The proposed analysis technique has been successfully validated through a series of analyses of constructed spectra. Furthermore, the technique was applied successfully for the analysis of a series of samples, proving of great value for the analysis of samples of environmental significance.