Investigation of self-attenuation of 210Pb (46 keV) gamma ray in sediment, certified reference material and high-density minerals: Implication to precise measurement of 210Pb

High resolution gamma spectrometry is one of the most widely used techniques in the measurements of envi-ronmental level Pb-210 in sediment from coastal and freshwater environments and such measurements are needed to establish Pb-210 chronology for the past 100-150 years. Precise measurement of( 210)Pb in sediment and soil requires appropriate self-absorption correction for its low-energy (46.5 keV) gamma radiation due to differences in the matrix between the sample and standard used to calibrate the instrument. Here we report a method that involves precise determination of( 210)Pb activity in sediment sample by calibrating the HPGe well detector with RGU-1-IAEA Certified Reference Material for well-defined geometries. A comparison of the Pb-210 activity ob-tained from gamma-ray spectrometry with that obtained from alpha spectrometry via Po-210, using( 209)Po as yield tracer, indicates good agreement. We propose an empirical relation between the absolute efficiencies and packing densities of sample in a well-defined geometry (cylindrical counting vial) by affecting the count rate of Pb-210 and its progenitor, Ra-226 (via Pb-214 and Bi-214). The effects of self-attenuation of 46.5 keV (Pb-210), for naturally-occurring high-density minerals (apatite, titanite, monazite, and cerite) are evaluated. Specific activity of Pb-210 on apatite measured by alpha and gamma spectrometry are compared. This study is relevant and useful for precise measurements of gamma-emitting environmental radionuclides such as Pb-210, Be-7, Cs-137 as well as Ra-226.

Automated summary

High resolution gamma spectrometry is a widely used technique for measuring environmental Pb-210 in sediment. This study presents a method for precise measurement of Pb-210 activity in sediment samples by calibrating the detector with a certified reference material. The study also investigates the self-attenuation effects of Pb-210 and compares the specific activity of Pb-210 measured by alpha and gamma spectrometry. The findings are relevant and useful for measuring gamma-emitting environmental radionuclides.