Raman mapping reveals alpha radiation damage zonation and its annealing in Durango apatite

The accumulation of alpha radiation damage and annealing mechanisms in apatite are crucial for thermochronological studies, yet they are challenging to explore. We conducted annealing experiments on four slices from one single Durango apatite crystal, utilizing Raman spectroscopy high-resolution mapping to investigate peak positions and full width at half maximum (FWHM) of the ν1(PO4) and ν3(PO4) bands. Additionally, LA-ICP-MS mapping was conducted on all samples to obtain their effective uranium content distribution. We assessed track density in various regions of the crystal, used a normalized track density reduction model to estimate original alpha radiation damage, and applied heavy ion irradiation to simulate the fission process and enhance the visibility of confined tracks. Our analysis shows that the FWHM of the ν1(PO4) band in Durango apatite is a reliable indicator of alpha radiation damage accumulation and does not correlate with fission track damage. We also found that the alpha radiation damage has negligible effect on fission-track annealing in young samples. While Raman peak position behaviour is still enigmatic, our results suggest that it may be influenced both by the chemical composition of apatite and by radiation damage accumulation. Our results underscore the potential of Raman spectroscopy as a powerful tool for assessing alpha radiation damage and annealing processes in apatite crystals.