239+240Pu and 90Sr deposition densities in undisturbed surface soil in Vietnam

Full text: The distribution of cumulative deposition of 137Cs in undisturbed surface soil was well investigated in Vietnam. However, this kind of study for 239+240Pu and 90Sr is still not performed in the country. In this work the cumulative deposition densities of 239+240Pu and 90Sr were measured and compared with that of 137Cs. 239+240Pu and 90Sr as well as 137Cs deposition densities in undisturbed surface soil are determined for 30 sites having different geographic and geo ecological conditions such as rainfall, soil properties, latitude, etc. Soil samples were taken at two depths, from the surface to 10 cm, and from 10 to 20 cm using a cylindrical corer with inner diameter of 4.2 cm. Soil properties such as texture, content of total organic matter, humic, fulvic were analysed for each sample. The samples were passed through a sieve with a mesh of <1 mm to remove coarse gravels and then calcinated. 137Cs in samples was analysed on a gamma spectrometer equipped with HPGe detector. About 50 gam of the dry soil was chemically treated and dissolved Pu was purified then electrochemically deposited on a stainless steel disk.239+240Pu was quantified on an alpha spectrometer equipped with PIPS detector. Another 500 gam of the sample was radiochemically treated and 90Sr was collected with strontium nitrate carrier. 90Sr in the samples was analysed through its daughter 90Y on a low level beta counting system. Quality control for the analytical results has been performed using IAEA reference material (Soil 4/2000) and the deviation between experimentally obtained results and certified values are within ±5 %. It was revealed that the 239+240Pu, 90Sr and 137Cs depositions in undisturbed surface soil in this study vary within a range of 18-96 Bq/m2, 171-1026 Bq/m2, 243-2965 Bq/m2, respectively. The ratios of 239+240Pu and 90Sr deposition densities to that of 137Cs vary from 0.02 to 0.22 and from 0.09 to 1.17, respectively. (author)