Study of plutonium redistribution in a raised peat bog following a fire

Abstract

Peat lands are archives of past diversity, climate, and other environmental conditions. The redistribution of radionuclides in a peat bog after a fire consists of change in vertical distribution and releases/losses to the atmosphere through evaporation and resuspension. The study of different radionuclides such as plutonium isotopes will be important to understand the radiation exposures to man following fire on contaminated land. In this work, a fast and sequential procedure for uranium, plutonium and americium determination in soil samples is presented. Together with the study of redistribution of uranium and plutonium isotopes in a raised peat bog located in the nature reserve of Vakö Mire (south of Sweden) following a big fire (1992). The procedure is based on the four main steps of any radiochemical procedure: pre-treatment, isolation of radionuclides, source preparation and measurement via alpha spectrometry. The sequential separation of the radionuclides is performed by extraction chromatography, employing UTEVA resin in columns and DGA resin in cartridges. Once the procedure was established, two cores of the Vakö Mire peat bog were studied (one from the burnt area and another from the not affected area). The first 10cm of each core sliced in 1 cm layers were analyzed. The results for plutonium in the burnt core show an increase in the 239+240Pu activity concentration (Bq/m2) at the ash layer, while in the not affected area the concentration slightly increases with depth due to the global fallout. Regarding uranium isotopes, their behaviour in the peat bog is different from plutonium. The non-burnt area presents much higher values of activity concentration than the burnt one due to its higher inorganic content. The fire made this element easily movable via weathering conditions and as results the U content in the burnt core is hardly 10% of the total amount accumulated in the non-burnt area. Moreover, 234U and 238U isotopes were found in secular equilibrium.