natural radioactivity of granites used as building materials in iran

the radionuclides 226ra, 232th and 40k concentrations measured as well as radiological parameters, for 14 granite samples that use in iran as building material were calculated. the measurements of the radioactivity concentrations were carried out at nuclear physics laboratory university of tabriz. this subject is important in environmental radiological protection, since granites are extensively used as building and ornamental stones. the external and internal hazard index and the annual effective dose rates index evaluated and compared to the limits proposed by united nation scientific committee on the effects of atomic radiation. radiation exposure dose rate and radium equivalent activity raeq for all samples under investigation were calculated. radium-equivalent activities (raeq) range from 210.50-450.72 bq/kg. in addition internal hazard index (hin) and external hazard index for evaluation of environmental risk have also been determined which range 0.81-1.63 and 0.57-1.22 respectively. recommended values for internal and external hazard index are 1.5 and 1 respectively. the annual effective doses of studied samples is calculated based on equations and conversion coefficient proposed by unscear which is 1.05 for one sample and ranges from 0.3 – 1 svg/y for other studied samples. according to european commission (ec, 1999), effective doses exceeding the dose criterion of 1 msv/y should be taken into account in terms of radiation protection.