Shielding performance of multi-metal nanoparticle composites for diagnostic radiology: an MCNPX and Geant4 study

Lead-free polymer composite shields are used in diagnostic radiology to protect patients from unnecessary radiation exposure. This study aimed to examine and introduce the radiation-shielding properties of single- and multi-metal nanoparticle (NP)-based composites containing Bi, W, and Sn using Geant4, MCNPX, and XCom for radiological applications. The mass attenuation coefficients and effective atomic numbers of single- and multi-metal NP-loaded polymer composites were calculated using the Geant4 and MCNPX simulation codes for X-ray energies of 20-140 keV. The nano-sized fillers inside the polydimethylsiloxane (PDMS:C₂H₆SiO) matrix included W (K = 69.5 keV), Bi (K = 90.5 keV), and Sn (K = 29.20 keV). For single-metal shields, one filler was used, while in multi-metal shields, two fillers were required. The MCNPX and Geant4 simulation results were compared with the XCom results. The multi-metal NP composites exhibited higher attenuation over a larger energy range owing to their attenuation windows. In addition, Bi₂O₃ + WO₃ NPs showed a 39% higher attenuation at 100-140 keV, and that of Bi₂O₃ + SnO₂ NPs was higher at 40-60 keV. Meanwhile, the WO₃ + SnO₂ NPs exhibited lower attenuation. The difference between the results obtained using Geant4 and XCom was less than 2%, because these codes have similar simulation structures. The results show that the shielding performance of the Bi₂O₃ + WO₃ filler is better than that of the other single- and multi-metal fillers. In addition, it was found that the Geant4 code was more accurate for simulating radiation composites.