An improved alpha scintillation counting method for determination of Th, U, Ra-226, Th-230 excess and Pa-231 excess in marine sediments

In a previous paper it was shown that thick-source α counting is a simple means for determining Th, U, Th-230 excess, and Pa-231 excess concentrations, and hence sedimentation rates, for deep-sea sediments. Here it is shown that radon escape can lead to inaccurate results if powdered samples are used and that this problem can be overcome by preparing samples as a borate glass before measurement. Glassed samples also permit a novel measurement of the Ra-226 content by measurement of the post-fusion buildup of Rn-222, a determination shown to be necessary for near-surface sediments that have a deficit of Ra-226. It is also shown that Po-210 is lost during the fusion and that this loss can be allowed for in the calculations. The above observations are found on comparisons of measured and calculated α count rates for several Th and U standards and on comparisons with α spectrometry results from four sets of deep-sea core samples