Influence of High-Z Filler Chemistry on the Energy-Dependent Gamma-Ray Shielding of Cement-Board Composites

Cement-board composites were prepared at a fixed nominal filler loading to compare the attenuation response of different high-Z additives under a common mass-fraction condition. A commercial cement board was used as the host matrix, and five formulations containing 30 wt% Bi2O3, BaSO4, HfO2, WO3, or Fe were fabricated and compared with a pure pressed control. X-ray diffraction (XRD) was used to examine phase-related structural features, while gamma-ray transmission was measured with 241Am (59.5 keV) and 137Cs (661.7 keV) using a collimated NaI(Tl) spectrometric arrangement. At 59.5 keV, the linear attenuation coefficient increased from 0.3909 cm−1 for the control to 0.6423, 1.8127, 2.5464, 2.6205, and 2.7828 cm−1 for Fe-, HfO2-, WO3-, BaSO4-, and Bi2O3-containing specimens, respectively. The corresponding half-value layer decreased from 1.773 cm to 1.079, 0.382, 0.272, 0.265, and 0.249 cm. At 661.7 keV, the modified specimens remained more attenuating than the control but clustered within 0.1731–0.1842 cm−1. Within the tested conditions, the fabricated formulations showed much stronger discrimination at 59.5 keV than at 661.7 keV, with Bi2O3-, BaSO4-, and WO3-containing specimens forming the strongest low-energy group. Because the pressed-disc densities differed between the formulations, these linear-attenuation differences are interpreted as the combined response of additive identity and the resulting bulk density/compaction rather than as a chemistry-only effect. This study is a fixed-loading, two-energy screening comparison rather than a concentration or structural optimization study.