Multi-analytical characterization and radiation shielding assessment of natural ophiolitic rocks: a combined...

Ophiolitic suites derived from oceanic crust are rich in ferromagnesian and mafic minerals and exhibit relatively high densities, making them promising and economical materials for radiation shielding. This study evaluates ophiolitic rocks exposed along the Marsa Alam-Idfu road in the southern Eastern Desert of Egypt as natural radiation shielding materials, including mafic metavolcanics, mafic schist, serpentinite peridotites, and hornblende metagabbro-diorite. Comprehensive geochemical analyses were conducted using polarizing microscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR) to constrain the mineralogical frameworks. Experimental γ-attenuation measurements were performed using a P-HPGe detector for Cs-137 (0.662 MeV) and Co-60 (1.173 and 1.332 MeV) sources. Monte Carlo simulations (MCNP-5) and EpiXs software were also employed to model photon interactions and validate the experimental results. The mineralogical assemblages of the investigated samples which predominantly composed of serpentine, chlorite, amphibole, plagioclase, talc, and carbonates, play a key role in controlling their radiation shielding properties. Geochemically, the rocks display a major oxide compositional range from ultramafic to mafic. Serpentinized peridotites, in particular, exhibit high MgO content and low silica, while mafic metavolcanics and schists are rich in Al₂O₃ and FeO. Radiation shielding results showed that the linear attenuation coefficients (µ) exhibited a pronounced decline with increasing photon energy, controlled by photoelectric and Compton interactions, with serpentinized peridotites showing the highest attenuation due to its greater density and high iron oxide content. Simulated and experimentally calculated µ values showed strong agreement (φ = 2.431%), while experimental results were slightly higher, with deviations ranging from - 3.6% to - 9.2%. The obtained trends of attenuation coefficient, half-value layer, tenth-value layer, effective atomic number, and radiation protection efficiency (RP_eff) further confirmed the energy-dependent attenuation behavior, identifying serpentinized peridotites as the most efficient γ-ray shielding material among the investigated rocks. Furthermore, Neutron-shielding assessment revealed that serpentinized peridotites exhibited the highest fast neutron removal cross-Sect.  (0.097 cm^- 1) and the lowest half-value layer (7.121 cm) and relaxation length (10.273 cm), indicating superior neutron attenuation performance among the investigated lithologies.