Natural uranium isotopes and 226 Ra in surface and groundwater from a basin of a semiarid region in Brazil
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Natural uranium isotopes and 226Ra in surface and groundwater from a basin of a semiarid region in Brazil Lino Valcarcel Rojas1 · José Araújo dos Santos Júnior1 · José Antonio Corcho Alvarado2 · Marvic Ortueta Milan1 · Stefan Röllin2 · Romilton Santos Amaral1 · Zahily Herrero Fernández1 · Josineide Marques do Nascimento Santos1 Received: 11 May 2020 / Accepted: 13 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract This research aimed to get information about the uranium and radium activity concentrations in surface and ground water in a semiarid region in Brazil. Mean (and range) activity of 0.46 (0.01–1.8), 0.015 (0.0004–0.066) and 0.32 (0.09–1.32) Bq L− 1 were found for 234U, 235U and 238U, respectively. Uranium radioisotopes account for the higher radioactivity in surface and groundwater, 226Ra was found only in few groundwater samples (0.09–0.61 Bq L− 1). 226Ra/238U (0.15–0.43) and 234U/238U (1.18–1.86) activity ratios are indicative of radioactive disequilibrium in groundwater. Expected effective doses from few water sources can be considered significant if untreated water is used for drinking. Keywords Uranium isotopic ratios · Dose assessment · Radioactive equilibrium · Semiarid region
Introduction
* Lino Valcarcel Rojas [email protected] José Araújo dos Santos Júnior [email protected] José Antonio Corcho Alvarado [email protected] Marvic Ortueta Milan [email protected] Stefan Röllin [email protected] Romilton Santos Amaral [email protected] Zahily Herrero Fernández [email protected] Josineide Marques do Nascimento Santos [email protected] 1
Grupo de Radioecologia, Departamento de Energia Nuclear (DEN), Centro de Tecnologia e Geociências (CTG), Universidade Federal de Pernambuco (UFPE), Avenida Professor Luiz Freire, 1000, Cidade Universitária, Recife, PE 50740‑545, Brazil
Spiez Laboratory, Nuclear Chemistry Division, Federal Office for Civil Protection, 3700 Spiez, Switzerland
2
Radioactivity is naturally present in all environmental com‑ partments, including surface and ground water. The main contributors to the radioactivity in water are the naturally occurring radionuclides from the three natural decay chains [1], and to a less extent 40K. Uranium (U), radium (Ra) and radon (Rn) radioisotopes are by far the most important contributors in water. Uranium has three naturally occur‑ ring isotopes (238U, 235U and 234U), with 238U representing approximately 99.27% of the mass of the element [2]. 238U and 235U are head of two radioactive decay series. However, due to their relative abundances, only the contribution of the 238 U series is considered important. Within the 238U series, the isotopes with a relevant contribution to the radioactivity in water are 238U, 234U, 226Ra and 222Rn, all of them alpha emitters. This is explained by their relatively high solubility in water. The chemical composition of ground water, and its level of radioactivity, is mainly controlled by the mineral compo‑ sition of the rocks with which the water interacts within the aquifer. High c
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