Distribution of238U,232Th,40K, and 137Cs concentrations in soil samples nearby a nuclear laboratory, Capao Island, Brazil

Abstract

Absolute soil concentrations of 238U, 232Th, 40K, and 137Cs sam ples were mea sured us ing high-resolution gamma spectrometry. The area of interest encompasses an embankment in a man grove swamp in Guaratiba, Rio de Ja neiro, called Capao Island, where nu clear, 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 signif icant environ mental im pact has re sulted from neu tron phys ics ex per iments performed in a graphite ex po nen tial pile in ad dition to the operation of two cesium-driven irradiating facilities, radiation monitoring of the iso topes was car ried out. A total of eight 250 ml soil samples were ex tracted within an area of 300 m 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 ex pected nor mal range for 232Th (60% of sam ples) and 40K (20% of samples) should be attrib uted to the construc tion debris (cement, rocks, and sand) used in the em bank ment at the site. Since there is no handling of those isotopes at that site or adjacent fa cilities that could af fect their pres ence, it was con cluded that no de tect able contamination has occurred.