Comparison of three measuring techniques performances to quantify Am-241 in different samples from laboratory experiments carried out under controlled conditions.

M. Morello, C. Colle and G. Grasset Actes du congrès ECORAD, 3-7 sept 2001, Aix en Provence, France Radioprotection - Colloques, volume 37, C1-933/ C1-937.

Theoretically, alpha and gamma emission rates of Am-241 are intense enough to be actually used through three different radioactive measuring techniques, gamma spectrometry, liquid scintillation and alpha spectrometry. From an experimental point of view, it is very important to choose the less time-consuming method for measuring the isotopes activities from collected samples. Unfortunately, (for the metrologists) the behaviour of such an isotope as the Am-241 in a natural environment results in samples with very low incorporated activities. This is particularly true in terrestrial areas where transfers from soils to grown up plants are weak. Such a phenomenon leads to a wide range of sample contamination levels where, for example, soil activity can differ from plant activity by several orders of magnitude. Depending on what the radioecological study is about, the metrologist has to apply the optimal measurement method regarding simultaneously, the sensitivity to be reached with the required sample preparation. In general, the lower is the sample activity, the more accurate the detection technique to discriminate between the effective signal from isotope under measurement and noise from natural ambient radioactivity must be. Spectrometric measurement techniques give, in this case, a quantitative result completed by qualitative information on reading the corresponding spectrum.