استجابة أشعة جاما الإشعاعية في بعض الوحدات الليثولوجية لصخور الدهر الوسيط المنكشفة في منطقة غريان شمال غرب ليبيا

* Department, of Geophysics Faculty of Sciences, University of Tripoli

Mesozoic sedimentary rocks are exposed in Gharyan area NW Libya. The age of these rocks ranges from Ladinian/Carnian beds exposed in some hillocks in the foot plain of Jabal Nefusa around the city of Al Azizia up to Cenomanian Nalut ( previously Gharyan) formation over which the city of Gharyan is settled. The formations are composed of different lithological units, and are interbeded locally in some areas with igneous intrusions and extrusions along with some tectonic elements such as faults. Gamma rays are small bursts of very high frequency electromagnetic waves that are spontaneously emitted by the nuclei of some isotopes of some elements. Only a limited number of isotopes of the natural elements emit gamma rays; and among these, there are only three which are: Potassium (K), Uranium (U) and Thorium (Th). K is a major constituent of most rocks and is the predominant alteration element in most mineral deposits. Uranium and thorium are present in trace amounts, as mobile and immobile elements, respectively .As the concentration of these different radioelements varies between different rock types, we can use the information provided by a gamma-ray spectrometer to map the rocks. SPP2 Gamma Ray Scintillometer and RS320 Gamma Ray Spectrometr were used in this study to measure the gamma ray radioactivity of the different units of the geological formations in the area. The measured radioactivity range of the different units in the measured channels was: total radioactive channel (222 ppm –

2920 ppm); potassium (0.3% - 7.3%), Uranium (0.7ppm – 14.3ppm), Thorium (0.6ppm – 23.7ppm), and total gamma ray scintilometry (15 c/s to 180 c/s). The measured geophysical radioactive data showed a very well accordance with the different geological units. This work is an attempt to denote the natural radioactivity of the lithological units exposed in jabal Nefusa in Gharyan area and it is the first is kind of such study and will serve as a guide line to any radioactivity survey or study that will be carried in the future in this area or the surrounding areas.