Measurement of radon at NMBU : concentration, seasonal variation and dose estimation

Radon-222 is radioactive noble gas which is formed by the decay of Radium-226, which is the decay product of the Uranium-238. Radon-222 and its decay products have the negative effect on health, hence it becomes a major concern when the radon is presence in higher concentration in buildings with poor ventilation or with strong source. Increasing amount of indoor radon concentration is huge problems in Norway in comparison to other countries. It is estimated that more than 300 deaths from lung cancer occurs in each year due to indoor radon in Norway. Life expectancy can be increases by 14 to 18 years on avoiding of lung cancer. Norway, Sweden and Finland are the countries having the highest level of radon in the world, perhaps due to the geological condition and cool climatic condition. But at the same time the radon problem can be eliminated in cost effective ways. This research work is performed at NMBU (Norwegian University of life Sciences) Ås Norway. As the NMBU is an academic institution where the large number of students, employees, and researchers are conducting their own work. Therefore, this study investigated the radon concentration, seasonal variation, annual occupational dose in the study area which can be helpful to reduce the existing radon concentration level if it exceeds beyond the action level. The objective was to measures the radon concentration in different three building in terms of their ages. As well the measurements were done in two different season viz summer and winter season. The annual dose was also calculated for the professional, and employees who spend their times at NMBU. The portable radon monitor (PMR145) was used for radon measurement. The samples were taken and measure in June, July and August which is supposed to be the pick summer season and November, December, and January which is supposed to the pick winter season. At the same time, Background samples were also taken and measured in summer and winter season to calibrate with indoor radiation. In selected three buildings, measurements were done in underground, first, second and third floor. In each floor one room was randomly selected either. In each floor and room five samples were taken to find the more variability. All the collected data were calculated and analysed in Ms-Excel, Mini-Tab 17 and R studio. For investigating the radon concentration on different buildings and different season, significant test < 0.005 were done statistically significant. For calculating the annual dose equilibrium factor 0.4, dose conversion factor 9 and occupancy level supposed (44 weeks X 37.5h) = 1650 h for full time working employees were taken. The study shows that indoor radon concentration varies in summer and winter season specifically in underground floor of tower building. The highest average radon concentration with standard deviation 147±59 Bq/m3 and minimum to maximum range of radon concentration (44-197) Bq/m3 was detected in underground floor of tower building in summer season while highest average radon concentration with standard deviation 56±27 Bq/m3 and minimum to maximum range of radon concentration (17-79) Bq/m3 was detected in winter season in tower building. Anova Tukey test was performed to investigate the significant difference in mean levels of radon concentration in between floors in different buildings, and it was found that there is significant difference (P < 0.005, 95% confidence level) in between underground to first, second and third floor. Similarly, one way ANOVA was performed to find the seasonal variation in buildings and floors and the results revels that radon concentration is significantly difference (P < 0.005, 95%) in summer and winter. Furthermore, annual occupational dose were calculated, considering the dose conversion factor 9 nSv/Bq/h/m3, equilibrium factor 0.4, and occupancy used in the study (44 weeks X 37.5h) and it was found that maximum annual dose was found to 1.0 mSv/y in underground floor of tower Building in summer season. On the basis of this research work following facts can be concluded. In all the three building the radon concentration was found to be less then action level 100 Bq/m3 accept Underground floors. The action level is recommended by Norwegian regulation protection authority. The seasonal variation in radon concentration indicates that higher radon concentration was in summer and minimum in winter. The highest radon concentration and annual dose was found at underground floors in summer season which indicates that there is need to take some action to reducing it.submittedVersionM-RA