اندازه گيري تشعشعات زمينه طبيعي استان چهارمحال و بختياري

Measurement of natural background radiation in Chaharmahal and Bakhtiari province

The presence of natural background radiation and environmental radioactivity is due to distribution of radionuclides in the earth and cosmic rays. These causes exposure to biological area and human body. In most countries natural background radiation has been measured repeatedly, but there is no accurate and complete information in lran. The contents of natural radionuclides (uranium, actinium, and thorium) as well as the thin layer of atmosphere in the higher altitude regions are reasons of high level of human exposure. The aim of this survey was focused on determining the current background radiation of Chaharmahal and Bakhtiari province, which is the highest altitude region in Iran. The outdoorsʹ environmental monitoring exposure rate of radiation was measured in 100 randomly selected regions using a portable Geiger-Muller detector. Eight measurements were made for each region and averaged as exposure rate of natural background radiation of that region. The mean exposure rate was found to be 28.2+_1.4 miuR/h and an overall outdoor dose rate was 49 nGy/h which is higher than the worldwide mean value of 44 nGy/h as reported in UNSCEAR, 1998. The annual effective dose equivalent was found to be 0.49 mSv/y. The results showed that there is a good correlation between altitude and exposure rate. ln relation to the altitude and geological structure of the province the results also showed that the higher altitude regions has the higher natural background radiation level.