Pages: 149-153

Authors: Luciano S. R. Oliveira, Celio J. V. Oliveira, Bruno M. R. Carvalho, Paulo A. M. Cabral, Helio C. Vital and Edson R. Andrade

Abstract

Absolute soil concentrations of ²³⁸U, ²³²Th, ⁴⁰K, and ¹³⁷Cs samples were measured using high-resolution gamma spectrometry. The area of interest encompasses an embankment in a mangrove swamp in Guaratiba, Rio de Janeiro, called Capao Island, where nuclear, chemical and biological defense laboratories of the Brazilian Army Technology Center are in operation for more than 30 years. In order to ensure that no significant environmental impact has resulted from neutron physics experiments performed in a graphite exponential pile in addition to the operation of two cesium-driven irradiating facilities, radiation monitoring of the isotopes was carried out. A total of eight 250 ml soil samples were extracted within an area of 300 m x 300 m. No trace of ¹³⁷Cs was detected and the measured levels of ²³⁸U were found to be close to the global mean. However, some data that slightly exceeded the expected normal range for ²³²Th (60 % of samples) and 40K (20 % of samples) should be attributed to the construction debris (cement, rocks, and sand) used in the embankment at the site. Since there is no handling of those isotopes at that site or adjacent facilities that could affect their presence, it was concluded that no detectable contamination has occurred.

Key words: gamma-ray spectroscopy, soil, ²³⁸U, ²³²Th, ⁴⁰K, ¹³⁷Cs

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