Soil gas radon ²²²Rn concentration was measured at 12 location in the Al-Qassim area, using radon gas analyzer-type Alpha GUARD 2000 PRQ from Genitron Instruments (Germany). In each location four different depths were taken for soil gas measurements, staring from the ground sur- face. The results suggested that the largest con- centration was 340 ± 22 Bq/m³ for 60cm depth at in Al-Tarfia point sample P3, and the smallest concentration was 26 ± 5 Bq/m³ for surface 0 cm depth at El-Bakria, point sample P5. The results obtained from this study indicate that the region has background radioactivity levels within the natural limits.

The natural radioactivity of 226 Cs in soil and rock samples under investigation, are not radiologically important. The radium equivalent activity (Raeq) and external hazard index (Hex) of all samples are less than the limits of 370 Bq·kg −1 and unity, respectively. The average values of total absorbed dose rate due to three primordial radionuclides in soil and rock samples are 46.5 nGy/h and 138.36 nGy/h, respectively, where the absorbed average value of the granite is higher than the permitted limit. So, the local people must avoid using these granite samples as the interior decorative materials of dwelling without radioactivity control. Ra