Public effective doses from environmental natural gamma exposures indoors and outdoors in Iran

Abstract

The effective doses of public in Iran due to external gamma exposures from terrestrial radionuclides and from cosmic radiation indoors and outdoors of normal natural background radiation areas were determined by measurements and by calculations. For direct measurements, three measurement methods were used including a NaI(TI) scintillation survey meter for preliminary screening, a pressurised ionising chamber for more precise measurements and early warning measurement equipment systems. Measurements were carried out in a large number of locations indoors and outdoors ∼1000 houses selected randomly in 36 large cities of Iran. The external gamma doses of public from living indoors and outdoors were also calculated based on the radioactivity measurements of samples taken from soil and building materials by gamma spectrometry using a high-resolution HPGe system. The national mean background gamma dose rates in air indoors and outdoors based on measurements are 126.9±24.3 and 111.7±17.72 nGy h(-1), respectively. When the contribution from cosmic rays was excluded, the values indoors and outdoors are 109.2±20.2 and 70.2±20.59.4 nGy h(-1), respectively. The dose rates determined for indoors and outdoors by calculations are 101.5±9.2 and 72.2±9.4 nGy h(-1), respectively, which are in good agreement with directly measured dose rates within statistical variations. By considering a population-weighted mean for terrestrial radiation, the ratio of indoor to outdoor dose rates is 1.55. The mean annual effective dose of each individual member of the public from terrestrial radionuclides and cosmic radiation, indoors and outdoors, is 0.86±0.16 mSv y(-1) by measurements and 0.8±0.2 mSv y(-1) by calculations. The results of this national survey of public annual effective doses from national natural background external gamma radiation determined by measurements and calculations indoors and outdoors of 1000 houses in 36 cities of Iran are presented and discussed.