TITLE:
Accurate Determination of 232Th through 208Tl Using Ultra-Low Background Gamma Spectrometry in Environmental Matrices
AUTHORS:
Abdul J. Khan, Umme-Farzana Syed, Cynthia A. Costello
KEYWORDS:
232Th, 208Tl, Soil, Sediment, Ultra-Low Background Gamma Spectrometry, True Coincidence Summing
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.14 No.4,
April
8,
2026
ABSTRACT: Accurate measurement of thorium-232 (232Th) in environmental samples is essential for geochemical research, ecological monitoring, and radiological safety. Because 232Th emits gamma radiation at a low probability, its activity is often estimated from short-lived daughter isotopes such as 228Ac, 212Pb, 212Bi, and 208Tl, assuming secular equilibrium. This study used ultra-low-background high-purity germanium (HPGe) gamma spectrometry to measure the 232Th activity in certified reference materials and environmental sediment and soil samples. The 2614.5 keV gamma line of 208Tl provided the most accurate and consistent results, although corrections for true coincidence summing (TCS) effects were necessary. Gamma lines from 228Ac and 212Pb exhibited minimal summing losses, which helped verify equilibrium-based measurements. Statistical analysis confirmed consistency across all daughter nuclides, validating the use of 208Tl and related decay products for 232Th determination. This method proves effective for routine environmental analysis and regulatory compliance.