الفهرس 
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Abstract
Measurement of radioactivity of naturally occurring radioactive materials (NORM) is of great interest in various Earth science fields of study; like exploration, environmental monitoring and classification of soil and rocks. These radioactive nuclides are typically measured by means of Gamma-ray Spectrometry and by means of Neutron Activation Analysis. In this thesis, four natural radioactivity measurement techniques (two techniques of Gamma-ray Spectroscopy and two techniques of Neutron Activation Analysis) are compared, mainly on the basis of their accuracy and their detection capacity. Two reference (standard) and three field samples were subjected to be analyzed, for the concentration of their natural radionuclides (specifically, U-238, Th-232 and K-40), by Normal-Mode Gamma-Ray Spectroscopy, Compton Suppression Gamma-Ray Spectroscopy, Thermal Instrumental Neutron Activation Analysis and Epithermal Instrumental Neutron Activation. All the results of mass concentration of Uranium and Thorium in the reference sample, IAEA-312, obtained using the four stated techniques of measurement of natural radioactivity were seen to be in good agreement with their respective values of specifications given by the IAEA, in which the En-score results for all the measurements were calculated and found to be less than unity. These show that all the four techniques of measurement, which are used in determination of natural radioactivity in this thesis are verified to be practicable regarding to their accuracy. Moreover, the values of En-score for all the measurements were least in the measurements taken by the Normal-Mode Gamma-ray Spectrometry technique of measurement, this shows that the Normal-Mode Gamma Spectrometry showed the best accuracy than the other techniques of measurements used in this thesis work. The minimum detectable concentrations of Uranium, Thorium and Potasium-40 are observed to differ with respect to the samples and methods as well. However, the trends of variability of the detection capacity of the techniques were seen to be similar for all the samples. Generally, for all the samples, the detection limit for Uranium has the least value in the Compton Suppression Gamma-ray Spectroscopy and the detection limit for Thorium has the least value in Thermal Neutron Activation Analysis. The detection limit for Potassium-40, which was measured in the two Gamma-ray Spectrometry techniques only, is less in the Compton Suppression Gamma-ray Spectroscopy than in Normal-Mode Gamma-ray Spectroscopy. The measurements based on the four techniques show that the mass concentrations of U, Th and K-40 in the three field samples to be ranged, respectively, from 1.79+0.08 to 4.97+0.69, 4.20+0.33 to 14.47+1.30 and 1.64+0.02 to 2.98+0.01 in units of mg/kg. The corresponding external radiation hazard indices (Hex) for all the samples were calculated to be 2.19+0.14, 1.98+0.09, 0.22+0.01, 0.48+0.03 and 0.56+0.04 for samples IAEA-312, IAEA-313, ISE-1, ISE-2 and ISE-3 respectively.