Natural gamma radioactivity in granites with different weathering degrees: A case study in Braga (NW Portugal)

Abstract

Granite is one of the most radioactive rocks due mainly to their content in K, U e Th. In order to assess radiation risks in historical buildings, a gamma radiation assessment has been made in quarry samples of the Braga granite with different weathering degree. Using gamma spectrometry, the specific activities of U and Th, decay chains and radioactive K, were measured. The specific activities of radionuclides were used to calculate the gamma building index (I < inf > ? < /inf > ) of the EU technical guidance (RP112) for regulatory control of building materials, and to estimate some radiological hazardous parameters such as: the average radium equivalent activity (Ra < inf > eq < /inf > ), Annual Gonadal Equivalent Dose (AGED), the absorbed dose and the annual effective doses. All the samples exceed the I < inf > ? < /inf > value of 1 and the indoor air annual effective dose rate in excess due to buildings materials can be higher than 1 mSv y < sup > -1 < /sup > in the more weathering samples.