STUDY OF QUENCHING EFFECTS WHEN MEASURING SOFT β EMITTERS IN ENVIRONMENTAL SAMPLES BY LSC AND ITS APPLICATION TO DETERMINE

ABSTRACT. Using liquid scintillation counting (LSC), 241Pu is usually measured after isolating the Pu isotopes and then electroplating onto planchets via supported-disc LSC (SD-LSC) to minimize quenching problems that might have appeared when dissolving the precipitate deposited on the disc. However, if those quenching problems are carefully controlled or cor-rected, the measurement of 241Pu activity, once dissolved from the disc, could well be valid. In this paper, we approached the problem of measuring 241Pu directly from the disc in 2 ways: a procedure of Pu dissolution from the planchet is developed in parallel with a study of the chemical quenching in these kinds of environmental samples to obtain the counting efficiency of the measurement of 241Pu by LSC. In relation to the SD-LSC method, an increase in counting efficiency was observed using our radiochemical procedure. Finally, we propose a validation of the LS technique by measuring the 241Pu in electroplated lacustrine sediment samples using an accurate alternative technique consisting of counting the ingrowth of the 241Pu alpha-emitting daughters. To use this technique, the samples must have been electroplated at least 5 yr ago to let the alpha daughters grow in the disc. The activities obtained using both techniques are in good agreement