Beta spectrometry for environmental radioactivity measurements

¹ Laboratoire de Mesure de la Radioactivité de l'Environnement (LMRE), IPSN, bâtiment 501, Bois des Rames, 91400 Orsay cedex, France
² Laboratoire pour l'Utilisation du Rayonnement Électromagnetique (LURE), bâtiment 209D, Université Paris-Sud, 91405 Orsay cedex, France

Abstract

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 (T_1/2 = 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 β_max 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.