Is density a reliable predictor of X-ray and gamma attenuation in oxide glasses?

Transparent oxide glasses are widely studied for X-ray and gamma shielding in applications requiring optical access. Material selection is often guided by density, assuming that higher-density glasses provide superior attenuation. However, the reliability of density as a predictive parameter under practical engineering constraints, particularly when both thickness and mass requirements are considered, remains insufficiently clarified. In this work, six experimentally reported oxide glass systems spanning densities from 2.23 to 7.16 g·cm⁻³ were evaluated at photon energies of 0.08, 0.662, and 1.25 MeV, covering the transition from photoelectric- to Compton-dominated interaction regimes. Mass attenuation coefficients (μ/ρ) were obtained from XCOM data, and the thickness and areal mass required to achieve 90% attenuation (1 TVL) were derived under narrow-beam conditions. Results reveal a clear distinction between thickness-based and mass-based shielding performance. Increasing density and incorporation of high-Z elements systematically reduce the required shielding thickness, particularly at low photon energies where photoelectric absorption dominates. At 0.08 MeV, tellurite- and bismuth-containing glasses exhibit significantly enhanced attenuation, leading to very small TVL thicknesses compared with silicate compositions. However, the corresponding areal-mass differences remain less pronounced than the thickness differences. At 0.662 and 1.25 MeV, attenuation differences between the investigated glasses become progressively smaller as Compton scattering becomes dominant. The results show that shielding performance depends strongly on photon energy and glass composition, and that higher density alone is not a reliable predictor of mass-efficient shielding across different energy regimes.