Increasing the sensitivity of Pu-241-determination for emission- and immission-control of nuclear installations by aid of liquid scintillation counting

Despite the Pu-241-concentrations in nuclear fuel to be reprocessed is high, up to now only few results are available concerning the emissions of Pu-241 with liquid and gaseous effluents and the environmental contamination in the surroundings of nuclear installations by Pu-241. The reason for this fact surely is the difficult measurement of Pu-241, a pure β-emitter with a β-energy of 21 keV. A procedure was developed and optimized which allows to measure Pu-241 very sensitively in all kinds of sample materials. In a first step, Pu isotopes are separated from matrix elements, cleaned radiochemically, electroplated, and measured by α-spectrometry. Then, the deposited Pu is redissolved in nitric acid and extracted with trioctylphosphinic oxide. The organic phase is mixed with scintillator cocktail and measured with a liquid scintillation counter. The detection limit of the optimized procedure for a counting time of 100 minutes is 40 mBq Pu-241 per sample