Investigation of the effect of material structure on radiation protection by Monte Carlo simulation method

Materials with high linear attenuation coefficients enhance radiation absorption by promoting greater interaction and energy deposition of ionizing radiation. The linear attenuation coefficient (LAC), a key parameter for protection against ionizing radiation, increases proportionally with material density, making denser materials more effective for radiation shielding. In this study, the linear attenuation coefficients and half-value layer values for four different polymorphs of PbO were obtained using the Monte Carlo simulation code MCNPX. These parameters were determined for monoenergetic gamma sources at energies of 140 keV (Tc-99m), 364 keV (I-131), 662 keV (Cs-137), and 1332 keV (Co-60) using a narrow beam geometry with 10⁷ particle interactions. The relationship between the crystal structures of the PbO polymorphs and the effectiveness of the radiation shielding was also assessed. Among the polymorphs, the orthorhombic PbO, characterized by an 8-atom Pbcm space group and mmm point group, a density of 9.14 g/cm³, and a unit cell volume of 162.16 Å³, exhibited the highest LAC, with an average increase of 13.67 % across all energy levels. Additionally, it was observed that the orthorhombic PbO, with the 8-atom Pbcm space group and mmm point group, which has the highest density (9.14 g/cm³) and unit cell volume (162.16 Å³), provides the most effective reduction in radiation with the least material thickness. In conclusion, the study demonstrates a direct correlation between changes in the crystal structure and the density of the compound. The use of different crystal structures of the same material offers a significant advantage in selecting materials for radiation shielding.