The electron densities (Ne) for both zircons have been determined from Eq.(4), and the result is shown in Table 4. The results show that the values of Ne for both zircons were decreased with increasing of gamma ray energies, shown also in Fig. 5. Despite there are significantly different major and minor compositions of Cambodian and South Africa’s zircons. It is seen that the trend of Ne for Cambodian and South Africa’s zircons are similar. This result are reflected to the value of Ne are not only depend on composition but it may be related to structure of zircon