International Journal of the Physical Sciences Vol. 5(6), pp. 696-699, June 2010 Available online at http://www.academicjournals.org/IJPS ISSN 1992 - 1950 © 2010 Academic Journals Full Length Research Paper Measurement of radon concentration inside houses in Tafila Province, Jordan O. Abu-Haija 1 *, B. Salameh 1 , A. W. Ajlouni 1 , M. Abdelsalam 1 and H. Al-Ebaisat 2 1 Applied Physics Department, Tafila Technical University, Tafila-Jordan. 2 Chemistry Department, Tafila Technical University, Tafila-Jordan. Accepted 31 May, 2010 The scope of this paper is to present a brief study related to the investigations we have already made at three districts of Tafila province, which is located in the south part of Jordan and where the most important hot spa and phosphate mines are located. The main concern in these investigations is to measure the indoor radon concentration levels by means of CR-39 detectors installed in randomly selected houses during winter season. The exposure time started from December 2008 and lasted for ninety days. After exposure, the detectors were etched in a KOH solution at 70°C for 8 h. The obtained average values of indoor radon concentration in the three different districts were ranged from 20.45 to 32.41 Bq/m 3 . It was found out that the Ayma district possesses the highest radon concentration. Meanwhile, the district of Aina Al-Badah possesses the lowest. Key words: Indoor radon, CR-39, passive dosimeter, exposure time. INTRODUCTION Radon is a radioactive noble gas that is formed as natural deposits of uranium throughout the earth's crust decay. As radon decay products are inhaled, they can mutate the cells in the lungs. These alterations can increase the potential for getting lung cancer (ICRP, 1987). Moreover, a radon gas is considered to be the second leading cause of lung cancer behind smoking. It turned out that a large part of natural dose to human population comes from radon ( 222 Rn) and its progeny (UNSCEAR, 2000). This health risk comes from the fact that the radon gas and its airborne daughters can seep up from the ground and build up in enclosures like dwellings. As a result, nationwide measurements of radon concentration levels inside dwellings (indoor) have received numerous interests from research professionals and are continuously presented all over the world (NRC, 1999). It is also of great importance to assess the exposure to ( 222 Rn) and its progeny in houses and areas of high 222 Rn levels for the purposes of quality control, radioactivity monitoring of building materials and for correction measures recommendations. Therefore we believe that it *Corresponding author. E-mail: oabuhaija@ttu.edu.jo. Tel: +962 7 99027889. Fax: +962 3 2250002. is crucially important to perform a measurement on the indoor radon concentration levels in a large number of randomly selected houses in different locations of Tafila province in Jordan since the indoor radon levels depend on many factors like the geological nature of the site under study, the nature of the soil, the meteorological conditions, the social habits of the dwellers and the porosity as well as the density of the wall material. Most of the dwellings in the study area and its surrounding are without any compliance to regulatory standards and are typical for one family having four to five rooms. The dwellings surveyed were of different types, but were mainly made of stones with cement. Xerochreptic soil constitutes more than 73% of this region with high stone content in the soil. The prevalent kinds of stone in the study area are limestone, sandstone, crushed and Marl. Moreover, a higher ventilation rate was exercised during the daytime inside the dwellings surveyed since doors and windows were open most of the day, in turn this can circulate the air in the dwellings and introduce a fresh air. It is interesting to mention that many authors studied the indoor radon concentration levels in Jordan. Among them Al-Kofahi et al. (1992) have obtained radon concentration levels in the city of Irbid. Abumurad et al. (1997) have been made a comprehensive study of radon levels in Jordanian dwellings in all Jordan cities during an