Determination of natural Ra isotopes in samples from northern Sao Paulo state coastal area

The present work aims the determination of natural Ra isotopes in coastal samples collected at Ubatuba region, with the application of the obtained inventories to estimate coastal water mixing rates and assess submarine groundwater discharge. Since these radionuclides are present in sea water in trace form (10''-16 g/ L), the methodology included pre-concentration of huge volumes of sea water using MnO2 coated acrylic fiber, leaching of these fibers in HCl media and co-precipitation of the long-lived Ra isotopes with BaSO4. Before long-lived radium isotopes determination, the isotopes 223Ra e 224Ra were quantified using a delayed coincidence system. The delayed coincidence system utilizes the difference in decay constants of the short-lived Po daughters of radon 219Rn and 220Rn to identify alpha particles derived from its decay products. The activities of 226Ra and 228Ra were determined by gross alpha and beta counting respectively, of the Ba(Ra)SO4 precipitate in low-level gas flow proportional detector. Considering the results obtained in 2002 and 2003, the coastal waters exchange time were estimated for Flamengo, Fortaleza and Mar Virado embayments using the activity concentrations of 223Ra, 224Ra, 226Ra and 228Ra. (author)