The use of gamma-rays analysis by HPGe detector to assess the gross alpha and beta activities in waters

Autor(es)

Casagrande, M. F. S. ^[1] ; Bonotto, D. M. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Estadual Paulista, UNESP, Dept Petrol & Metalogenia, Av 24-A 1515, CP 178, BR-13506900 Rio Claro, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Applied Radiation and Isotopes; v. 137, p. 1-11, JUL 2018.
• Citações Web of Science: 1

Resumo

This paper describes an alternative method for evaluating gross alpha and beta radioactivity in waters by using gamma-rays analysis performed with hyper-pure germanium detector (HPGe). Several gamma emissions related to a and beta(-) decays were used to provide the activity concentration data due to natural radionuclides commonly present in waters like K-40 and those belonging to the U-238 and Th-232 decay series. The most suitable gamma emissions related to beta(-) decays were Bi-214 (1120.29 keV, U-238 series) and 2 degrees 8 11 (583.19 keV, Th-232 series) as the equation in activity concentration yielded values compatible to those generated by the formula taking into account the detection efficiency. The absence of isolated and intense gamma-rays peaks associated to a decays limited the choice to Ra-226 (186.21 key, U-238 series) and Ra-224 (240.99 keV, Th-232 series). In these cases, it was adopted appropriate correction factors involving the absolute intensities and specific activities for avoiding the interferences of other gamma-rays energies. The critical level of detection across the 186-1461 keV energy region corresponded to 0.010, 0.023, 0.038, 0.086, and 0.042 Bq/L, respectively, for Ra-226, Ra-224, Tl-208, Bi-214 and K-40. It is much lower than the WHO guideline reference value for gross alpha (0.5 Bq/L) and beta (1.0 Bq/L) in waters. The method applicability was checked by the analysis of groundwater samples from different aquifer systems occurring in the Brazilian states of Sao Paulo, Minas Gerais and Mato Grosso do Sul. The waters exhibit very different chemical composition and the samples with the highest radioactivity levels were those associated with lithotypes possessing enhanced uranium and thorium levels. The technique allowed directly discard the K-40 contribution to the gross beta activity as potassium is an essential element for humans. (AU)

• Processo FAPESP: 16/03054-2 - Estudo radiométrico integrado em estâncias hidrominerais dos estados de São Paulo e Minas Gerais
• Beneficiário: Daniel Marcos Bonotto
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 15/03974-1 - Metodologia alternativa para caracterização da radioatividade alfa e beta total nas águas
• Beneficiário: Matheus Felipe Stanfoca Casagrande
• Modalidade de apoio: Bolsas no Brasil - Iniciação Científica