Feasibility of ZrSiO4 as reference signature in naturally-occurring radioactive elements for the application of radioactivity monitoring

Radioactivity monitoring post-cold war has become more complex due to the nuclear fallout and the surge in use of radioactive materials. This requires novel methods to detect, trace and distinguish natural and anthropogenic radioactive sources in the environment. We explored the feasibility of using ZrSiO4 (Zircon), as a reference signature for radioactivity monitoring due to the unique phenomenon of metamictization. We investigated the variations in microstructural properties of Zircon samples collected from a proposed Uranium site to identify these signatures using analytical techniques such as Gamma-ray Spectroscopy, XRD and Raman spectrum analysis. Besides elevated levels of radioactivity, the samples exhibited distinct properties such as increased lattice parameters observed from the XRD analysis and dramatic broadening of A1g (439 cm(-1)) and B1g (1008 cm(-)1) vibrational modes in the Raman spectrum. Structural parameters were further analyzed by modeling the crystal from experimentally observed lattice parameters. Ab-initio calculations were then performed on the modeled structure providing more insight into the microstructural variations. Samples collected from proposed Uranium mines indicate an increase of 1.226% and 0.9389% in Si-O and Zr-O bond lengths of the Zircon crystal signifying the ongoing process of metamictization from radiation damage. By correlating radioactivity levels with the lattice parameters variations of the collected samples, the study establishes a linear relation between the degree of damage to a mineral's crystal structure and the amount of radioactivity. We propose to use the variations in damage found in a mineral's structure as a nuclear forensic signature for advanced assessment of accumulated radioactivity in a particular geographical location.