Raman Spectroscopy Evolution of Swift Proton Induced Structural Damage as a Function of Fluence

This study systematically investigates and identifies ion-beam-induced structural degradation patterns in commercial zinc white paint, a material highly relevant to cultural heritage artifacts examined under external analytical beams. Utilizing the electrostatic tandem accelerator setup at LAMFI-USP, samples from two distinct preparation batches were irradiated with a 2.4 MeV external proton beam commonly used for Particle-Induced X-ray Emission (PIXE) analysis, under systematically varied currents, exposure times, and overall fluences. The resulting structural modifications were characterized via Raman spectroscopy, with data processing involving targeted baseline corrections to isolate the vibrational modes of the pigment from formulation-induced fluorescence. Quantitative analysis of the Raman parameters as a function of fluence revealed two highly reproducible linear trends: a progressive broadening of the peak FWHM (slope = 0.0091) indicating lattice amorphization, and a concurrent systematic decrease in height ratio (slope = -0.00013). This simultaneous evolution establishes a differential degradation rate, confirming that the monitored vibrational modes associated with the organic paint formulation components diminish faster than the stable crystalline matrix. Ultimately, these predictable Raman fingerprints define crucial damage thresholds, providing a reliable diagnostic framework to ensure the safe, non-destructive analysis of heritage coatings under external ion beams.