Comparative X-ray Shielding Properties of Single-Layered and Multi-Layered Bi 2 O 3 /NR Composites: Simulation and Numerical Studies.

This work theoretically compared the X-ray attenuation capabilities in natural rubber (NR) composites containing bismuth oxide (Bi 2 O 3 ) by determining the effects of multi-layered structures on the shielding properties of the composites using two different software packages (XCOM and PHITS). The shielding properties of the single-layered and multi-layered Bi 2 O 3 /NR composites investigated consisted of the transmission factor (I/I 0 ), effective linear attenuation coefficient (µ eff ), effective mass attenuation coefficient (µ m,eff ), and effective half-value layer (HVL eff ). The results, with good agreement between those obtained from XCOM and PHITS (with less than 5% differences), indicated that the three-layered NR composites (sample#4), with the layer arrangement of pristine NR (layer#1)-Bi 2 O 3 /NR (layer#2)-pristine NR (layer#3), had relatively higher X-ray shielding properties than either a single-layer or the other multi-layered structures for all X-ray energies investigated (50, 100, 150, and 200 keV) due to its relatively larger effective percentage by weight of Bi 2 O 3 in the composites. Furthermore, by varying the Bi 2 O 3 contents in the middle layer (layer#2) of sample#4 from 10 to 90 wt.%, the results revealed that the overall X-ray shielding properties of the NR composites were further enhanced with additional filler, as evidenced by the highest values of µ eff and µ m,eff and the lowest values of I/I 0 and HVL eff observed in the 90 wt.% Bi 2 O 3 /NR composites. In addition, the recommended Bi 2 O 3 contents for the actual production of three-layered Bi 2 O 3 /NR composites (the same layer structure as sample#4) were determined by finding the least Bi 2 O 3 content that enabled the sample to attenuate incident X-rays with equal efficiency to that of a 0.5-mm lead sheet (with an effective lead equivalence of 0.5 mmPb). The results suggested that the recommended Bi 2 O 3 contents in layer#2 were 82, 72, and 64 wt.% for the combined 6 mm, 9 mm, and 12 mm samples, respectively.