Beta spectrometry for environmental radioactivity measurements.
A. Courti*, P. Bouisset and P. Chevallier
Actes du congrès ECORAD, 3-7 sept 2001, Aix en Provence, France
Radioprotection - Colloques, volume 37, C1-911/ C1-916.
* étudiant en contrat de thèse au laboratoire
Various anthropogenic sources contribute to the inventory of long lived beta emitters in the environment (40K, 210Pb, 60Co, 137Cs, 90Sr, 90Y). Studies have been carried out to obtain the 90Sr distribution in environment in order to estimate its impact in terms of radiation exposure to humans.
It is routinely measured it by proportional counter after radiochemistry. An incomplete radiochemical separation leads to a deposit submitted to count polluted by natural beta emitters. In order to guarantee results, 90Y daughter of 90Sr, is systematically extracted from the final radiochemical fraction and counted. The 90Y decreasing (T1/2 = 2.67 days) is checked by 2 hours successive counts during 64 hours. The delay between the end of radiochemistry and the counting is 15 days imposed for the radioactive equilibrium between 90Sr and 90Y to be reached. The duration from the beginning of the radiochemistry to the result of the measurement is of the order of five weeks.
In order to diminish this procedure, and in order to detect several radionuclides simultaneously, we study the possibility of a beta spectrometer based on two PIPS (Planar Passivated Implanted Silicon Canberra) solid detectors. Because of their different bmax energies and to their spectral features (continuum shape, conversion electrons), we have shown that the main radionuclides like 137Cs and 90Sr can be discriminated. The identification is independent of the source geometry. However, the quantification requires a well defined and reproducible geometry, for which a shorter radiochemical procedure is being studied. Real sample results will be presented.