¹²⁹I determination by direct gamma-X spectrometry and its application to concentration variations in two seaweed species

¹ IRSN/DEI/STEME/Environmental Radioactivity Measurement Laboratory, Bât. 501, Bois des Rames, 91400 Orsay, France, e-mail: evelyne.barker@irsn.fr
² IRSN/DEI/SECRE/Octeville-Cherbourg Radioecology Laboratory, Rue Max Pol Fouchet, BP. 10, 50130 Octeville, France
³ EDF, 6 quai Watier, 78401 Chatou Cedex, France

Abstract

The quantification of radionuclides by direct gamma-X spectrometry with energy below 100 keV requires knowledge the elementary composition of the sample or the development of a device for determining the mass attenuation coefficients. This is especially true for ¹²⁹I which is characterised by a 29.8 keV X-ray and 39.6 keV gamma ray. Experimental equipment has been developed in order to obtain this mass attenuation coefficient as a function of energy. ¹²⁹I concentrations were measured in samples of seaweed (Fucus serratus and Laminaria digitata) collected monthly over a period of one year nearby La Hague reprocessing plant in France. This paper describes the measurement methodology used to determine ¹²⁹I concentrations and variations in the two seaweeds over a one-year period. Mean mass attenuation coefficients for ¹²⁹I energies were established in order to determine the self-attenuation corrective factor for both seaweed species, regardless of the sampling date.