Abstract

       Radon is a radioactive gas that is produced naturally from the natural radioactive decay of radium which produces from decomposition of uranium . In this study, radon concentrations were measured in the air of buildings for some schools in the city of Karbala . The study was carried out using closed and open passive radon dosimeters containing two types of solid state nuclear track detectors types of organic detectors  such as cellulose nitrate LR-115 Type II and CN-85 with thickness 12 μm for each detectors. Fifty schools were selected randomly from schools in Karbala city, 100 dosimeters were distributed (50 open and 50 closed dosimeters) on the selected schools for period about three month in winter. These dosimeters put at height about two meters from the ground. the detectors were collected and alpha particle traces were appeared  after etching the detectors in sodium hydroxide solution at a concentration of 2.5 N for 90 minute at temperature of ( 60 ± 1) ºC, after that the detectors washed with distilled water and dried for the purpose of counting the effects of alpha particles using an optical microscope with magnification 100X .

       The results showed that the mean of radon concentration in air of school buildings was 36.972±11.33 and 36.481±9.66 in open dosimeters for LR-115 Type II and CN-85 respectively. In closed dosimeters, radon concentrations were found 24.249±5.70 and 26.275±6.49  for LR-115 Type II and CN-85 respectively. After calculating the radon concentrations in open and closed dosimeters, it found  the mean equilibrium factor was 0.143 and 0.089, the mean value of annual effective dose was found 0.064  and 0.037  in open dosimeters and found 0.035 , 0.023  in closed dosimeters for LR-115 Type II and CN-85, respectively. In addition, the mean potential alpha energy concentration was calculated as equal to 1.680 mWL and 0.974  mWL in open dosimeters ,either in closed dosimeters were  0.935 mWL and 0.600 mWL for LR-115 Type II and CN-85, respectively . The mean value of exposure to radon progeny were 11.259 mWLMY^-1 and 6.525 mWLMY^-1 in open dosimeters ,either in closed dosimeters were  6.258 mWLMY^-1 and 4.019 mWLMY^-1 for LR-115 Type II and CN-85, respectively. The mean value of lung cancer cases per year per million person was 1.147 and 0.665 for open dosimeters, 0.638 and 0.410 in closed dosimeters for LR-115Type II and CN-85, respectively. The results were obtained from this study within the international limits (200-300) according to ICRP, that’s mean there is no risk of lung cancer threatening students and educational staff of these schools.