Determination of 241Pu in evnironmental samples by liquid scintillation counting: preliminary report

The determination of 241pu in envirionmental samples carried out in this laboratory earlier were based on the measurements of the 241Am content of platinum discs onto which the plutonium fractions of the samples were electrodeposited two to three years earlier. The disadvantages of this method is that a waiting period of several years is needed before the 140Pu-content of the sample can be determined. Even after this time, the amount of 241Am built up by decaying of 241Pu is small and thus the counting statistics remain poor. The aim of this work was to develop a method for determination of low 241Pu concentrations in environmental samples by automated liquid scintillation counting. The 241Pu concentration of lichen, beard-moss and reindeer liver samples was determined by the method described. The 241Pu results as well as the 239240Pu concentrations are given. In addition, the activity ratio 241Pu/239240Pu is indicated. The highest 241Pu value, 6500 pCi/kg dry wt., was found in a beard-moss sample collected in 1966. The detection limit of the counting system is about 1 pCi using a counting time of 300 minutes. During analysis of the fourteen samples analyzed no contamination due to other beta-activities was found