Abstract

Granitoid rocks belonging to plutons of Greece, covering a wide range of compositions and rock-types, have been studied for their specific activity (Bq/kg) of 238U and 226Ra from 238U radioactive series and 228Ra and 228Th from 232Th radioactive series by using gamma-ray spectroscopy. Results on the radioactive secular equilibrium of both 238U and 232Th radioactive series are presented by studying the 226Ra/238U and 228Ra/228Th ratios. The majority of the samples are in radioactive secular equilibrium for 226Ra/238U±1σ. However, several samples exhibit 226Ra/238U ratios significantly different from 1. The distortion of the secular equilibrium in the 226Ra–238U isotopic system of those samples has occurred over the last 1Ma, and can be associated with post-magmatic processes, mainly rock–water interactions. All studied samples have 228Ra/228Th ratios equal to unity ±1σ. Consequently, they can be considered to be in secular equilibrium for the last 40a.

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