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Service Radioactivité

Many of the methods of environmental studies in radioactivity involve analysis of samples in a radiochemistry laboratory. Although the sample media and sample preparation vary, the basic analytical methods are used for all types of samples. Many nuclides of interest in the vicinity of nuclear facilities can be ascertained by gamma-ray spectrometry, which often requires little or no sample preparation. Radionuclides that emit only alpha or beta radiation cannot be analyzed by gamma spectroscopy. Examples of these nuclides are Pu-239 and Sr-90 alone, and many of the radionuclides in the natural series. Measurement of gross beta and gross alpha are often used to screen samples for alpha and beta emitters. If predetermined screening levels are exceeded, then, more complex analytical chemistry techniques are used to analyze specific nuclides. Tritium, which is a weak beta emitter, is usually measured in a liquid scintillation counter. Several compendia of analytical methods for radionuclides in environment media are available (Chieco et al., 1990 ; IAEA, 1989 ; Bodnar and Percival, 1982 ; NCRP, 1986a).

In LGGE, the present studies of basic parameters such as absolute dating and radiochronology, accumulation rates (snow and sediments) and their respective spatial and temporal variations, transfer and deposition processes, are extensively determined thanks to the radiochemical analysis and to the great sensitivities (and high resolution) of gamma and alpha spectrometries, as well as low level beta counting.

The radioactivity detection equipment adapted particularly for low-level, environmental measurements, in LGGE, is described in the following sections.

References :

Bodnar, L.Z. and Percival, D.R., 1982. RESL Analytical Chemistry Branch procedures manual. Report IDO-12096 US Department of Energy, Idaho Falls, Idaho.

Chieco, N.A., Bogen, D.C. and Knutson, E.O. eds, 1990. EML procedures manual. Report HASL-300, DOE Environmental Measurements Laboratory, New York.

IAEA, 1989. Measurement of radionuclides in food and the environment – a guide – book