In Table 3, the effective atomic number of Cambodian’s zircon is found to be decreasing from 22.9427 e /atom to 19.2668 e /atom while in South African’s zircon it decreases from 18.4203 e /atom to 15.6301 e /atom with increasing gamma ray energies from 223 to 662 keV. The experimental values of effective atomic number are in good agreement with the theoretical values and the statistical uncertainties were found to be in the range 3–4% as shown in Table 3. The results show that there are significant differences in the effective atomic numbers between the Cambodian and the South African’s zircons for the energy range studied as shown in Fig. 4.This is due to the differences in the ZrO2 and SiO2 compositions of Cambodian and South African’s zircons.