Direct gamma-X spectrometry measurement of 129I in environmental samples using experimental self-absorption corrections

Direct gamma-X spectrometry is a suitable technique for quantifying low-level I-129 activity, down to a few becquerels per kilogram, in environmental samples. Direct gamma-X spectrometry is a non-destructive technique that is rapid, which can be used for measuring several radioisotopes (multielementary) and that is easy to implement. A description is given of an experimental method for determining the self-absorption correction in the low-energy range, below 25 keV, to quantify I-129 in different environmental matrices. The method is based on the measurement of the mass energy-attenuation coefficient mu(m)(E) of the sample and the standard used to calibrate the measuring system. The mu(m)(E) data are introduced in a simplified formulation of the correction factor that is validated for several container-detector sets commonly used in low-level activity environmental measurement. The method has also been tested on I-125, I-129 and Cs-137, using different energy transitions. For marine algae species with high iodine concentrations (>2 x 10(-3) as a fraction of mass), an original method of determining the I-129/I-total ratio as against the mu(m)(E) determination in the vicinity of the iodine K-absorption edge energy is described. (C) 1999 Elsevier Science B.V. All rights reserved.