Gamma radiation in rocks used as building materials: the Braga granite (NW Portugal)

Abstract

[Abstract]Granite can be a rock with significative radioactivity levels due to its content in radioisotopes of K, U e Th. The Braga granite has been extensively used from the past in historical buildings of this city in North Portugal. A gamma radiation assessment has been made in quarry samples of the Braga granite with different weathering degree, in order to assess radiation risks in historical buildings, derived from their content in radionuclides. The specific activities of radioisotopes in 238U and 232Th decay chains and radioactive 40K were measured by gamma spectrometry on samples with different weathering degree. The results were used to calculate the gamma building index (Iγ; EU technical guidance RP112) a other indices to estimate the radiological hazard of the rock as building material. Specific activities are above world averages and all the samples have Ig >1 (the threshold that implies specific studies for building materials). This result can be especially relevant for historical building where this granite is used as bulk material.