الملخص

ABSTRACT In order to find a universal empirical relationship among the absolute efficiency of a photopeak, the energy of gamma ray and the distance from the source to the detector face, we used a modern gamma-ray spectroscopy called (SPECTECH UCS-20) with a scintillation detector, NaI(Tl), of dimensions 3.8cm(diameter)×2.5cm(thick). The system is connected to a personal computer with a program installed for this purpose. The absolute efficiency have been found using standard radioactive sources (Na-22, Mn-54, Co-60, Cd-109, Eu-152) in the energy range (88-1408) keV and a distance (1.25-10.25)cm. A fit to the figure of measured absolute efficiency with distance was applied, and we have found that the best fit is the power fit. Also we found the best equation to calculate the two constants, in the power fit equations .Thus we have combined the absolute efficiency, energy, and distance in one universal empirical equation. The experimental results have been compared with those calculated by the universal empirical equation and a good correspondence has been found between them .Further, we find detector efficiency of standard sample from (KCl) putted in touch to the detector surface, this efficiency can be used to calculate the concentration of (40k) in different situations.