Activity ratios of thorium isotopes in living species compared with other environmental samples

Kierepko, R., Mietelski, J.W., Gaca, P. and Tomankiewicz, Ewa (2008) Activity ratios of thorium isotopes in living species compared with other environmental samples. Nukleonika, 53 (1), 27-30.

Abstract

Since about ten years our laboratory is conducting studies on the determination of Pu in many environmental samples, among them also the biological ones. Plutonium results were already discussed elsewhere [1, 4, 5, 8–21, 27]. In the course of radiochemical procedure for plutonium separation a thorium fraction was separated for each sample. Since we had not used any thorium tracer in the past, thorium activities were not determined. However, always alpha sources were prepared and then measured. This produced a relatively large archive of thorium alpha spectra from which one can study activity ratios of thorium isotopes. Two ratios seems to be interesting. The first is the Th to Th activity ratio. Both these isotopes are the Th-series members and, therefore, one might expect equilibrium. Usually this is not the case. Another subject is the activity ratio between Th and Th. One can tell that there is no relation between these two isotopes and, therefore, this ratio should not bring any information. The first isotope belongs to the U series, it is a decay product of U. The second one is just a primordial parent of the Th series. So, one can expect, that this ratio will generally reflect the activity ratio between the U and Th series for a given environment. However, this ratio might be modified by weak effects and this possibility should be taken into consideration.

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