Determination of Iodine-129 in Samples of Conifers Collected in Argentina

INTRODUCTION I (t1/2 = 1.57.10 years) is produced in nature by spontaneous fission of natural uranium and spallation reactions of cosmic radiation with xenon in the upper atmosphere. Two important artificial sources are nuclear weapons tests and normal operation of nuclear facilities, which originate long-lived radioiodine, as a result of uranium fission. At present, the terrestrial equilibrium of the biosphere is strongly affected particularly near of nuclear reprocessing plants. Nowadays, I is important as a sensitive tracer for large-scale environmental processes and for surveillance of reprocessing of nuclear fuel, waste conditioning plants and final waste repositories. These are some of the reasons why detailed knowledge of background levels before the start of those operations and of possible current changes in the activity levels of all relevant environmental matrixes is necessary. In order to detect characteristic regional differences or variations in time in the levels of I, the concentration in the Argentine environment has been studied. There are two important nuclear techniques for the I analysis at environmental levels: radiochemical neutron activation analysis (RNAA) and accelerator mass spectrometry (AMS). An improved method developed at the A.R.N. laboratories has been used for the determination of I in conifers using RNNA. The method is simple and suitable for routine analysis. To perform it, a commercial charcoal for I adsorption and polypropylene tubes with low-sodium contents for reactor irradiation are needed. Clean-room laboratory conditions are necessary during pre-irradiation processing to prevent sample contamination. (2) The use of I as tracer allows the simultaneous determination of I activity and total recovery at the same time. Instead, when using I it is necessary to keep the sample up to decay of interferences, to eliminate Compton radiation before determining the chemical yield. 4)