Gamma-ray attenuation and spectral–angular transport in transparent graded-Z multilayer shields

Transparent radiation shields that combine photon attenuation with controlled secondary emission are relevant to medical imaging, nuclear medicine, and radiation-monitoring systems operating in the 0.06-1.33 MeV energy range. In this study, a graded-Z multilayer composed of bismuth-rich borosilicate (BBS), lutetium aluminium garnet (LuAG), and silica (SiO[Formula: see text]) is evaluated using GEANT4 Monte Carlo simulations and benchmarked against commercial RS-253 glass at matched areal density. The graded-Z structure exhibits higher mass attenuation coefficients and reduced half-value layers across the investigated energies. Comparison with representative Bi[Formula: see text]O[Formula: see text]-based glass systems from the literature indicates that the graded-Z design provides enhanced attenuation beyond composition-based optimization. Spectral analysis reveals energy-dependent fluorescence associated with the staggered K-edges of Bi and Lu, while angular scoring indicates enhanced forward-directed transmission relative to RS-253 at higher energies. These results show that graded-Z shielding modifies photon transport both spectrally and directionally. However, the multilayer design also increases forward-directed energy transport at higher energies, highlighting a tradeoff between attenuation performance and directional energy leakage. This simulation-based study establishes a quantitative framework for spectral-angular evaluation of transparent graded-Z shielding architectures. Experimental validation remains an important direction for future work.