Possibilities for determination of 241Am in environmental samples by gamma counting, with and without radiochemistry

Abstract

241Am emits 59.5 keV gamma rays with an abundance of 36%. The lower limits of detection achievable using efficient low energy gamma detectors, namely a low energy HP Ge detector of active area 20 cm2 and an HP Ge well-type detector (active volume 120 cm3) were studied. The low energy detector is more favourable for bulk samples, with an absolute counting efficiency for 100 cm3 samples of about 2%. For small samples (up to 5 cm3) the high efficiency of the well-type detector (20–30% absolute) is more advantageous. Limits of detection of 0.5 or 1 Bq kg−1 for soil or 0.1 Bq kg−1 (dry weight) for ashed biota were obtained. The concept of a simple concentration step to separate 241Am from the bulk of the sample by co-precipitation followed by high sensitivity gamma counting in the well-type detector was investigated, thus avoiding the lengthy radiochemical separation, electro-plating and alpha spectrometry of traditional procedures. A number of real (Cumbrian area) and spiked samples were examined and tracer experiments performed. The two techniques, non-destructive and with simple radiochemistry, show particular promise when rapid assays are required, e.g. in accidental releases.