Natural radioactivity and dose from marble used as building material

The activities of /sup 226/Ra, /sup 232/Th and /sup 40/K radionuclides have been measured in marble chips collected from the factories in Islamabad, Pakistan using NaI(TI) gamma ray spectrometer. The spectrometry system was calibrated with a reference material RGI obtained from IAEA. The activity measurements were based upon 1460.8 keV, 1764.5 keV and 2614.6 keV energies of /sup 40/K, /sup 226/Ra and /sup 232/Th, respectively. The spectrum stripping was done by matrix inversion method. The calculated specific activities of the marble samples varied from 4 Bq.kg/sup -1/ to 63 Bq.kg/sup -1/ for /sup 40/K. The Radium equivalent activities, have been calculated and were found to vary from 26 Bq.kg/sup -1/ to 100 Bq.kg/sup -1/, respectively. These values are within the limit by OECD (Ra /sub eq/ < 370 Bq.kg/sup -1/) and ICRP-60 (Ra/sub eq/ < 100 Bq.kg/sup -1/ for the safe use of the construction materials for dwelling. H/sub ex/ and h/sub in/ indices ranges from 0.0716 to 0.2692 and from 0.0831 to 0.4277, respectively which are also less than 1 according to OECD limit. The calculated values of overall absorbed dose rate for marble samples varies from 13 nGy.h/sup -1/ to 46 nGy.h/sup -1/. Dose rate (nGy/hr per Bq/kg) using Ingree code at a distance of 1 meter from floor varies from 10 to 65 for /sup 226/Ra, 11 to 53 for /sup 232/Th and 1 to 9 for /sup 40/K for all marble samples. All these results indicate that marble samples under study are safe for use as a construction material. (author)