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A national groundwater surveillance programme was started for investigation of natural radioactivity levels in the year 2007. This paper presents (222)Rn radioactivity concentration levels in well waters located in and around the city of Riyadh in Saudi Arabia. Water samples were collected from 171 wells in six different locations. Most of these deep wells have an approximate depth of 1000 m, while shallow wells have a depth of 300 m. The analyses were performed by an ultra-low level liquid scintillation spectrometer equipped with an alpha-beta discrimination device. Efficiency and background calibrations were performed with a (226)Ra aqueous standard homogeneously mixed with a cocktail (high efficiency mineral oil scintillator) which was used after a certain period of time to assure radon equilibrium. The measured (222)Rn activities of deep wells ranged from 0.34±0.05 to 3.52±0.30 Bq l(-1) (average: 1.01±0.10 Bq l(-1)), whereas those of shallow wells ranged from 0.72±0.08 to 7.21±0.58 Bq l(-1) (average: 2.74±0.24 Bq l(-1)). The (222)Rn concentrations levels were found to be in compliance with the proposed national limits of 11.1 Bql(-1) and depend on the water source.

The exposure of the population to natural gamma radiation in air and to indoor radon gas was investigated in Makkah, AlBaha, Assir, Jazan and Najran regions in the western and southwestern of Saudi Arabia. The survey was performed by using LiF:Mg,Cu,P thermoluminescence dosimeters (TLDs) for indoor and outdoor absorbed dose rates in air measurements in 885 locations, and a passive integrating ionizing system, equipped with an E-Perm Electret ion chamber, for radon concentration measurements in a total of 1119 dwellings. The ambient indoor rates vary from 54 to 191 nSv h−1, while it is in the range of 42–112 nSv h−1 for the outdoor. The indoor and outdoor rates of the directional dose equivalent ranged from 56 to 185 nSv h−1 and from 43 to 135 nSv h−1, respectively. Makkah region showed the highest mean indoor ambient and directional rates, whereas Assir region showed the highest mean outdoor rates. The indoor and outdoor gamma dose rates were significantly correlated. On the other hand, the indoor radon concentrations ranged from 11 to 137 Bq m−3 with an overall mean of 32 Bq m−3 for all investigated houses. The overall annual mean effective dose rate from radon and its decay progenies was estimated to be 0.76 mSv y−1, which yields an excess lifetime cancer risk of around 2.3 × 10−3.