Radiological studies in the hot spring region of Mahallat, Central Iran

Five hot springs called 'Abegarm-e-Mahallat', located in the central part of Iran, have a mean water temperature of 46 +/- 1 degrees C and are used by visitors as spas. This is an area of high natural radiation background due to the presence of Ra-226 and its decay products in the deposited travertine (CaCO3). The mean concentration of Ra-226 in these hot springs, measured by the emanation method, ranged from 0.48 +/- 0.05 to 1.35 +/- 0.13 Bq I-1. Rn-222 concentrations measured in the hot springs using a liquid scintillation counter ranged from 145 +/- 37 to 2731 +/- 98 Bq I-1. Mean radon concentrations in air were 487 +/- 160 and 15.4 +/- 2.7 Bq m(-3) for indoor and outdoor, respectively. Radiation levels above that of normal background (similar to 100 nGy h(-1)) were mainly limited to the Quaternary travertine formations in the vicinity of the hot springs. The results of environmental radiological studies in this region are presented and discussed.