<p>With the rapid advancement of industrial and technological applications, adequate protection against ionizing radiation has become increasingly critical. While radiation is widely utilized in medicine, energy, industry, and research, uncontrolled exposure poses serious biological risks. Heavy metals like lead have traditionally been used as shielding materials due to their high density and atomic number; however, their toxicity and environmental hazards have spurred the search for safer alternatives. In this context, eco-friendly, cost-effective, and industrially viable materials—particularly cement-based composites—have emerged as promising candidates for radiation shielding applications. This study systematically investigates the gamma radiation shielding performance of cement composites incorporating activated magnesium slag, a by-product generated during magnesium metal production at elevated temperatures under varying cooling conditions. Key shielding parameters—including mass attenuation coefficient (μ/ρ), linear attenuation coefficient (LAC), half-value layer (HVL), effective atomic number (Z_eff), and effective electron density (N_eff)—were evaluated both theoretically and experimentally across different photon energies (0.511, 0.662, 1.173, 1.275, and 1.332 MeV). The results reveal that the cement samples exhibit notably high μ/ρ values at low photon energy (0.511 MeV), while increased energy levels lead to a rise in HVL and LAC and a slight decrease in Z_eff and N_eff. Importantly, the cement produced with magnesium slag activated at high temperatures and rapidly cooled demonstrates photon attenuation capabilities comparable to the other samples. These findings highlight the potential of such sustainable composites as efficient and environmentally responsible shielding materials for gamma radiation in future applications.</p>