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

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

AIP Conf. Proc. -- August 7, 2008 -- Volume 1034, pp. 107-111
THE NATURAL RADIATION ENVIRONMENT: 8th International Symposium (NRE VIII); DOI:10.1063/1.2991186

Issue Date: 7 August 2008

J. Juri Ayub,a D. E. Di Gregorio,b,c H. Huck,b,c H. Velasco,a and M. Rizzottoa
aGrupo de Estudios Ambientales. Instituto de Matemática Aplicada San Luis. Universidad National de San Luis—CONICET. Ejercito de los Andes 950. Argentina
bDepartamento de Física, Comisión National de Energía Atómica, Av. Gral. Paz 1499, 1650 San Martín, Provincia de Buenos Aires, Argentina
cEscuela de Ciencia y Tecnología, Universidad National de San Martín. Martín de Irigoyen 3100, 1650 San Martín, Provincia de Buenos Aires, Argentina.
Beryllium-7 is a natural radionuclide that enters into 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. Rain traps were installed (1 m 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 40%-efficient p-type coaxial 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 was surrounded by 50 cm of lead bricks to provide shielding against radioactive background. The detector gamma efficiency was determined using a water solution with known amounts of chemical compounds containing long-lived naturally occurring radioisotopes, 176Lu, 138La and 40K. Due to the geometry of the sample and its position close to the detector, the efficiency points from the 176Lu decay, had to be corrected for summing effects. The measured samples were 400 ml in size and were counted curing one day. The 7Be detection limit for the present measurements was as low as 0.2 Bq l−1. Thirty two rain events were sampled and analyzed (November 2006-May 2007). The measured values show that the events corresponding to low rainfall (<20 mm) are characterized by significantly higher activity concentrations (Bq l−1). The activity concentration of each individual event varied from 0.8 to 3.5 Bq l−1, while precipitations varied between 4 and 70 mm. The integrated activity by event of 7Be was fitted with a model that takes into account the precipitation amount and the elapsed time between two rain events. The integrated activities calculated with this model show a good agreement with experimental values. ©2008 American Institute of Physics
Keywords: radioisotopes, beryllium, gamma-ray spectroscopy

DOI: 10.1063/1.2991186

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