Gamma Ray Exposure Measurements in the Vicinity of Jabal Hadb Ash Sharar and Jabal Sayid, Kingdom of Saudi Arabia
Ian C.F. Stewart
Data from an airborne radiometric survey has been used to estimate the gamma-ray exposure risk arising from the surface geology over an area about 50 by 25 km within the shield. This does not include exposure from other sources such as radon. The shield survey data was obtained by digitising hardcopy contour maps of potassium, thorium and uranium. Surface concentrations of the three elements were then used with standard equations to obtain grids of exposure values. While the calculated risk values are generally low (less than 1 mSv yr-1) over most of the surveyed area, there are some very localised areas where the values exceed this, with a maximum from the airborne data of about 13 mSv yr-1 near Jabal Sayid. Due to geometrical effects in airborne radiometric surveying, even higher values may therefore be expected in some places from ground data. Ground measurements of gamma-ray exposure were made at 25 locations near the highest airborne values as well as at other less active sites, including gravel plains away from major outcrops. The ground data indicates that in general higher values are observed on the ground and also the locations and amplitude of airborne anomalies may be affected signifi cantly by geometrical factors. Extremely high values (in excess of 150 mSv yr-1) were observed to the south of Jabal Sayid, and these are associated with an extensive outcrop of thoriterich pegmatite. The levels in this area pose an appreciable health risk, and suggest that more detailed mapping of exposure in the area is warranted.
Stewart, I.C.F., 2006, Gamma ray exposure measurements in the vicinity of Jabal Hadb ash Sharar and Jabal Sayid, Kingdom of Saudi Arabia: Saudi Geological Survey Data-File Report SGS-DF-2006-7, 13 p., 8 figs., 2 tables.