Determinación de índices alfa y gamma de granitos comúnmente usados como materiales de construcción en la ciudad de Riobamba

Abstract

In the present investigation, the risk indices associated with alpha and gamma radiation emitters present in the most commercialised granites in the city of Riobamba have been determined. The granite samples were crushed, pulverised, and dried at 105 degrees Celsius, then hermetically sealed and left to stand for four weeks. The material was analysed at the Subsecretaria de Control y Aplicaciones Nucleares (SCAN) using a high resolution germanium semiconductor detector (HPGe) and at the laboratory of Nuclear Techniques of the Escuela Superior Politécnica de Chimborazo, where a working technique was implemented using the Rug 91-2 spectrometer with a NaI(Tl) thallium-activated sodium iodide scintillator. The comparison of the results of the specific activity of K-40 obtained with the NaI (Tl) detector and the HPGe detector shows a trend of activity concentration measured with the scintillator higher than that measured with the semiconductor detector, except in the case of the Negro Galaxy granite where the opposite is observed, it is verified that the two detection systems have different efficiencies and therefore present heterogeneous results. The gamma index for the studied granites, calculated with the specific activities of K-40, Th-232 and Ra-226, reported by SCAN, show that the Violet granite presents a value of 6.72, therefore, its use in dwellings will contribute to exceed the reference level of external exposure due to gamma radiation indoors, the other four granites present typical values of 0. 04 to 0.80, on the other hand, the alpha indices varied between 0.10 and 0.80, consequently, the specific Ra-226 concentrations in all samples do not exceed the suggested value of 200Bq per kg. Finally, further studies with granite are recommended, using complementary techniques to ratify the results obtained in the investigation.