DÜŞÜK VE YÜKSEK ENERJİLİ GAMA IŞINLARININ MARUZ KALMA YIĞILMA FAKTÖRLERİNİN ETKİN ATOM NUMARASINA BAĞIMLILIĞI

Abstract

The Zeff dependence of exposure buildup factors for plane incident source gamma rays of 200keV, 500keV, 1MeV, 5MeV, 10MeV and 50MeV have been investigated by using electron gamma shower Monte Carlo code, EGS4. To prepare materials with different Zeff, homogen mixtures composed of Li, Cu, Fe and Pb were used in different ratios. All the EGS4 calculations were performed in two dimensional plane geometry for each mixture. To check the accuracy of EGS4 calculations, an extra work has been performed for the exposure buildup factors of Pb, Fe and H2O. Results of these calculations are agreed well with the published data. In the EGS4 calculations, the exposure was obtained from the photon flux and the energy absorption coefficient of air. The effect of Rayleigh scattering was included but effects of bremstrahlung and fluorescent radiation were not taken into account. All calculations were performed with the exponential transform. The calculated data showed that buildup factors vary smoothly with increasing Z. At deep penetration depths, variation of buildup factors has more rapid variation. The value of the buildup factor for an arbitrary atomic number can be obtained by using data resulted from this calculations