Self-absorption correction factor applied to 129I measurement by direct gamma-X spectrometry for Fucus serratus samples.

O. Lefèvre, P. Bouisset, P. Germain, E. Barker, G. Kerlau, X. Cagnat

Nuclear Instruments and Methods in Physics Research A 506,  173-185

Self-absorption corrections have been determined for the energies characterising 129I below 40 keV in the frame of studying Fucus serratus samples by direct gamma_X spectrometry. This work was performed on a large spatio-temporal scale in order to integrate the fluctuations of the matrix. More than 200 samples monthly collected from January 1983 to December 1996 along the  French Atlantic and English Channel coasts have been measured as part of the Permanent Observatory of the radioactivity programme of the Institut de Radioprotection et de Sûreté  Nucléaire (IRSN). A relationship has been established between experimental mass attenuation coefficients at low energy and the 40K concentrations of the samples, where the latter showed the same temporal variation as the 127I concentration (iodine stable isotope). Based on the mean correction factors determined in the present work, a simplified method is proposed to quantify the content of 129I. The direct gamma-X spectrometry results obtained in this way are in good agreement with those reported by Patti et al. (Radioprotection 23 (1988) 381) using neutron activation analysis for the samples collected between October 1983 and December 1984 at Herquemoulin, located near the La Hague reprocessing plant.