Investigation of Natural Radioactivity in Igneous Rocks and Estimation of Excess Lifetime Cancer Risk due to Gamma Radiation in Mahallat, Iran

Amount of natural background ionizing radiations in environment depends on kind of soil, stones and geographical conditions. Hot springs of Mahallat facilities are annually visited by many tourists. Determination of environmental radioactivity and excess lifetime cancer risk is very important.
In this research, twenty four samples of igneous and travertine rocks from a region (300 hectares) and four water samples of Mahallat hot springs were collected. The specific activities of radionuclides were determined for all samples by using gamma ray spectrometry method and employing high purity germanium detector with 30% relative efficiency.
External and internal hazard indices for igneous rocks, water and two travertine samples varied from 0.00 to 0.71 and for two another travertine samples obtained from 8.17 to 22.50. The average of annual gonadal dose equivalent (AGDE) was determined as 0.36 and 0.20 mSv/y and also the average of excess lifetime cancer risk (ELCR) was calculated as 0.23 × 10-3 and 0.12×10-3 for igneous and travertine rocks, respectively. Maximum acceptable value and world wide average of ELCR are 10-3 and 0.29×10-3, respectively.
The results of this research show that the hazard indices and ELCR for magma region are less than unity and world wide average respectively. Therefore; there is no consequence for people health. So, the radioactivity only around the orifice of hot springs where radium compositions are deposited, is more than maximum acceptable value.