  The natural radionuclide (Ra^222, Th^232, and 40K) contents were determined
for seven locations over the whole Wadi Arar at north of Saudi Arabia, using
gamma-spectrometry analysis. The range of activity concentrations of Ra^226,
Th^232, and 40 K in the soil varies from 19.8 up to 26.2 Bq/Kg, 8.56 up to
20.12 Bq/Kg and 132.89 up to 305.96 Bq/Kg respectively. The range of consumed
measurement rates from 19.64 to 34.77 nGyh^-1 for selected area. The range from
the radium equivalent (Req) extends from 42.27 to 73.71 Bq/kg the external
hazard index (Hex) range from 0.11 to 0.20 which is safe as construction
material. The radium equivalent was from for the selected areas, respectively.
The Geomorphological structure of the silty sand, soil and its correlation with
the gradient concentration of natural radioactivity (norm) in Wadi Arar was
discussed.
