Atmospheric deposition of 7Be by rain events, in central Argentina.

JURI AYUB, J.; DI GREGORIO, D.E.; HUCK, H.; VELASCO, R. H.; RIZZOTTO, M.

AIP CONFERENCE PROCEEDINGS

American Institute of Physics

Lugar: New York; Año: 2007

0094-243X

Beryllium-7 is a natural radionuclide that enters to the ecosystems through wet and dry depositions and has numerous environmental applications in terrestrial and aquatic ecosystems. Atmospheric wet deposition of 7Be was measured in central Argentina (San Luis province). Rain traps were installed (1m above ground) and individual rain events have been collected. Rain samples were filtered and analyzed by gamma spectrometry. The gamma counting was undertaken using a 1.033 kg intrinsic high-purity natural germanium crystal built by Princeton Gamma-Tech. The cryostat was made from electroformed high-purity copper using ultralow-background technology. The detector gamma efficiency was determined using a water solution with known amounts of chemical compounds containing long-lived natural radioisotpes, 176Lu, 138La and 40K. All rain samples of around 400 ml, were counted during 1 day. The 7Be detection limit for the present measurements was as low as 0.2 Bq l-1. 32 rain events were sampled and analyzed (November 2006-May 2007). Data show that events corresponding to low rainfall (<20 mm) are characterized by significantly higher activity concentrations (Bq l-1).  Initial activities of each individual event vary from 0.8 to 3.5 Bq l-1; and precipitations vary between 4 and 70 mm. The integrated activities by event of 7Be are fitted with a reload lineal model that takes account size precipitations and elapsed time between two rain events. This model estimated effectively wet deposition of 7Be and atmosphere reload in 1 day for latitude S30º.