[en] Measurement of beta emitters in environmental samples is actually based on radiochemical separation in the low-level case, or on the gross beta technique for control or accidental situations. We have studied the response function of a new detection system in order to discriminate by spectrometric methods beta and beta-gamma emitters. The idea is to use shorter radiochemical procedures for trace analysis, but still be able to detect and quantify eventual contaminations as well as get more qualitative and quantitative information than the one that gross beta technique can obtain. The set-up consists of two thin silicon detectors of large area, placed in a telescope configuration and working at room temperature. Our study has been realised with a series of pure sources having different spectrometric properties (³⁶Cl, ⁶⁰Co, ⁸⁵Sr, ⁹⁰Sr-⁹⁰Y, ¹⁰⁹Cd, ¹³⁴Cs, ¹³⁷Cs, ²⁰⁷Bi and ²⁴¹Am) in order to study in a second stage real environmental samples and their complex spectra. With this set-up we obtained detection limits lower than those based on the proportional counter in the case of ³⁶Cl and equivalent in the case of ⁹⁰Sr. Finally, improvements on the system are discussed. This system could be implemented for the measurement of low level samples after radiochemical separation or in accidental or post-accidental situation, in laboratory as well as in situ. (author)

[en] Various anthropogenic sources contribute to the inventory of long live β-emitters in the environment. 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. The Laboratory routinely measures ⁹⁰Sr by proportional counter after radiochemistry. An incomplete radiochemical separation leads to a deposit submitted to count polluted by natural β-emitters. In order to confirm the result, ⁹⁰Y (daughter of ⁹⁰Sr), is extracted from the final radiochemical fraction and counted. The ⁹⁰Y decreasing (T_1/2 = 2.67 days) is checked by successive counts over 64 h. The delay between the end of radiochemistry and the counting is imposed by 15 days to allow radioactive equilibrium between ⁹⁰Sr and ⁹⁰Y to be established. In order to remove this delay the purity of the ⁹⁰Sr fraction source can be verified by β-spectrometry. Thus, a β-spectrometer is under development in collaboration with Canberra Semi-Conductor and Canberra Electronic. It consists in a PIPS detector where several silicon layers are combined. Initial results will be presented in this paper

[en] Techniques used to quantify pure beta emitters (³H, ¹⁴C, ⁹⁰Sr, ³⁶Cl, ⁶³Ni...) in environmental matrices are based on a physico-chemistry selection of the element followed by liquid scintillation or proportional counting. We have studied a new method using thin Si (PIPS) detectors to obtain a spectrometric discrimination with or without the physico-chemical discrimination. Detection limits for pure sources are of the same order than values obtained with standard techniques with the advantage to identify other residual radionuclides. The part of natural radionuclide is important for surveillance measurement because global results induce complementary measurements. The spectrometry technique can discriminate natural and artificial contribution without necessity of detailed measurement even results above regular thresholds. (author)