226Ra and 228Ac in a Freshwater Ecosystem

Abstract

Abstract Uranium, thorium, and their decay products, being primordial radionuclides, are of interest in the nuclear fuel cycle. They have therefore been systematically considered in the radiological survey of the Portuguese rivers Douro and Tejo. We summarise survey data on 226Ra and 228Ac concentrations, in water, sediments, fish and acquatic macrophytes, determined by gamma spectrometry, and covering the period from 1976 to 1981 for the River Douro and 1976 to 1986 for the River Tejo. Field concentration factors (CF) and distribution coefficients (Kd) determined for these rivers have values within the following ranges: CF values in fish muscle, 49 to 52 for 226Ra and 41 to 49 for 228Ra; in aquatic macrophytes (1 to 1.5) x 103 for 226Ra and (0.75 to 1.1) x 103 for 228Ra; values of Kd in sediments (2.5 x 3.3) x 103 for 226Ra and (2.9 to 3.2) x 103 for 228Ra. These values are discussed. 228Ac/226Ra ratios for both rivers are compared and interpreted.