(4) w i = n i A i ∑ i n i A i Where, A i is the atomic weight of the sample, n i is a number of formula units. Validation Applying the Monte Carlo method is the one of the best solution for the investigation of different complex material behaviors since experimental duplication of investigation is quite complicated. So, it is more suitable to apply some numerical methods such as Monte Carlo [ 12]. In this paper, a validation for input code was performed. On the other hand, WinXcom program was also used to calculate the gamma ray mass attenuation coefficients of the studied shielding materials. WinXcom [ 13, 14] program is a user friendly calculation program and input parameter specifications are quite flexible and easy to access.

In the WinXcom program, firstly, shielding material types were defined by their elemental mass fractions, which are totally the same as in MCNPX Monte Carlo code input. Secondly, the gamma ray energies have been defined. The attenuation coefficients of the selected materials were finally calculated by the program. Results and Discussion MCNPX simulation input has been used for mass attenuation coefficients calculations of cement, gypsum and the mixture of gypsum and PbCO 3 materials. The mass attenuation coefficients for attenuator samples doped by different percentages of PbCO 3 were calculated for the four different energies 356, 662, 1,173, and 1,333 keV and shown in Figure 2. The standard XCOM data has been used for comparison with obtained MCNPX results. Figure 2 shows mass attenuation coefficinents of cement, gypsum and small doping of PbCO 3 in both the shielding materials.

It is found that the mass attenuation coefficients of pure and doped cement or gypsum are decreasing with increase in photon energy. This variation of mass attenuation coefficients can be explained using fundamental photon interaction process of photoelectric effect, compton effect and pair production for low-, intermediate- and high energy photons, respectively, which varies with atomic number of elements of compostions. From Figure 2A and 2C, it is to be noted that the mass attenuation coefficients of 100% cement and 100% gypsum estimated using MCNPX is lesser than theoretical data and comparable with experimental results. However, from Figure 2B and 2D it is observed that using MCNPX simulation, the mass attenuation coefficients of 100% cement and gypsum are lesser than 30% doping of PbCO 3. Doped cement and gypsum with PbCO 3 are found with large difference of mass attenuation coefficients at low energy (photoelectric effect region) compared with high energy (pair production region). It is because of Pb element of PbCO 3, which dominant for interaction in photoelectric effect region (interaction cross sectioin α Z 4–5).

Conclusion Mass attenuation coefficients of cement, gypsum and the mixture of gypsum and PbCO 3 has been investigated using monte carlo MCNPX. The simulated values of mass attenuation coefficients were compared available experimental results, theoretical XCOM values and found good comparability of the results. Standard simulation geometry for sample prepration of the present investigation would be very useful for various types of photon interaction investigations using MCNPX without experimental analysis for pure and mixture of elements. In addition, radiation safety inside medical areas, research centers, houses, nuclear shelters especially those close to nuclear power stations can be estimated by the calculation of shielding features of common cement and gypsium mixture materials.

Hubbell and S. Seltzer Tables and graphs of computed photon mass attenuation coefficients and mass energy-absorption coefficients from 1 keV to 20 MeV are presented for all of the elements (Z = 1 to 92) and for 48 compounds and mixtures of radiological interest.