Measurement of Be-7 in soils and sediments by gamma spectroscopy

作者：Landis Joshua D^*; Renshaw Carl E; Kaste James M

来源：Chemical Geology, 2012, 291: 175-185.

DOI：10.1016/j.chemgeo.2011.10.007

• Beryllium-7
• Gamma
• Interference
• Integration
• Precision
• Actinium-228

Measurement of cosmogenic Be-7 in soils and sediments by gamma spectroscopy has been routine for three decades. However, the analytical constraints of this method have yet to be adequately described. Natural abundance of Be-7 in bulk soils and sediments is typically low (10(6) to 10(8) atoms kg(-1)), resulting in very low signal-to-noise ratio in the gamma spectrum. Be-7 quantification is further complicated by numerous interferences from ubiquitous U-238- and Th-232-series radionuclides. We investigated the environmental gamma spectrum in the region of Be-7 emission using spectra obtained from hundreds of natural stream sediment samples, one well-characterized sediment naturally-enriched in Be-7, and pure standard materials enriched in both U-238-series and Th-232-series decay chains. In typical samples no fewer than three discrete photopeaks directly interfere with Be-7 measurement, one of which, the (228)AC 478.3 keV photon, yields significant positive bias. Risks of Be-7 false-positives due to this overlapping photopeak approach 50% for typical soils or sediments. Detection limits for Be-7 in these materials using conventional high-purity germanium instruments are as low as 0.1 Bq, but increase by up to a factor of four in the presence of modest activities of U-238- and Th-232-series nuclides. Here we demonstrate a methodology for the measurement of low Be-7 abundances in soils and sediments that is unbiased and that optimizes precision.

• 出版日期2012-1-6