Bismuth Oxide Films for X-ray shielding: Effects of particle size and structural morphology

Lead (Pb) as a traditional shielding material is limited due to its toxicity and heaviness. Recently, nanomaterials in different forms have attracted considerable attention for radiation shielding applications, due to their prominent chemical and physical properties. This work aims to evaluate the effects of size and morphology on the X-ray shielding performance. Both micro- and nano-sized Bi2O3 films with different morphologies (e.g. particles, wires, flowers) were synthesized via a ball milling process and a hydrothermal treatment, respectively. X-ray transmission tests were conducted using a superficial X-ray unit at energies of 30, 50 and 80 kVp (effective energies converted as 14, 24 and 29 keV), which were then compared with mass attenuation coefficient of Bi2O3 obtained from XCOM database. The results showed that the nanoflower (388 ± 30 nm) Bi2O3 film gave the best X-ray shielding performance among all three energies (60.49% improvement at 30 kVp, especially) compared to the bulk Bi2O3 film, indicating the synergy effects of both particle size and morphologies impact on low energies of X-ray attenuation. Moreover, the nanoparticle (830 ± 30 nm) Bi2O3 film enhanced the X-ray attenuation, up to 13.27% at 30 kVp relative to microparticle (1.21 ± 0.14 μm) films. However, the nanoflower (388 ± 30 nm) Bi2O3 film gave the best X-ray shielding performance (45.93% and 47.49% improvement at 30 kVp, respectively) compared to the microwire (1.30 ± 0.13 μm) and nanoparticle (830 ± 30 nm) Bi2O3 film, due to its large surface-to-volume ratio, showing that morphological variations can significantly impact the X-ray transmission to enhance the radiation shielding performance compared to the particle size. Theoretical data from XCOM database compared with experimental measurements showed the limitation of simulation as it can only calculate the ideal condition of regular distributions in materials with standardized geometry. This work concluded that the synergy effect of the particle size and morphology should be considered when designing effective radioprotective garments.