Volumic activities measurements and equivalent doses calculation of indoor 222Rn in Morocco

Abstract

Purpose: As a way of prevention, we have measured the volumic activities of indoor ²²²Rn and we have calculated the corresponding effective dose in some dwellings and enclosed areas in Morocco. Seasonal variation of Radon activities and Relationships between variation of these activities and some parameters such height, depth and type of construction were also established in this work.

Methods: The passive time-integrated method of using a solid state nuclear track detector (LR-115 type II) was employed. These films, cut in pieces of 3.4 ´ 2.5 cm², were placed in detector holders and enclosed in heat-scaled polyethylene bags.

Results: The measured volumic activities of radon vary in houses, between 31 and 136 Bq/m³ (0.55 and 2.39 mSv/year) with an average value of 80 Bq/m³ (1.41 mSv/year). In enclosed work area, they vary between 60 Bq/m³ (0.38 mSv/year) in an ordinary area to 1884 Bq/m³ (11.9 mSv/year) at not airy underground level of 12 m. the relatively higher volumic activities of ²²²Rn in houses were measured in Youssoufia and khouribga towns situated in regions rich in phosphate deposits. Measurements at the geophysical observatory of Berchid show that the volumic activity of radon increases with depth, this is most probably due to decreased ventilation.

Conclusion: The obtained results show that the effective dose calculated for indoor dwellings are comparable to those obtained in other regions in the word. The risks related to the volumic activities of indoor radon could be avoided by simple precautions such the continuous ventilation. The reached high value of above 1884 Bq/m³ don't present any risk for workers health in the geophysical observatory of Berchid because workers spend only a few minutes by day in the cellar to control and reregister data.