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Analysis of cultural heritage samples by PIXE involves the risk of damaging precious samples due to MeV-proton irradiation. To investigate appropriate methods to detect invisible damage due to PIXE analysis, we analyzed the change in chemical bonding of the sample surface subjected to PIXE and RBS measurement by Fourier Transform InfraRed spectroscopy (FT-IR). We used Japanese hemp paper as a simulated cultural property sample. The proton irradiation for the PIXE/RBS measurement was performed in a vacuum with an incident beam energy of 2.5 MeV, a beam current of 1 nA, and an irradiation time up to 10 min. The corresponding beam flux and fluence were 0.06 nA/mm2 and 4 μ Coulomb/cm2, respectively. When the irradiation time was 10 min, the absorbed dose was 480 kGy on the sample surface. We identified neither change of elemental composition nor visible change such as discoloration due to irradiation. However, we found changes in peak heights in the measured FT-IR spectra, which suggest the destruction of chemical bonds such as O–H and C–O due to proton-induced radiation damage. [ABSTRACT FROM AUTHOR]

Chemical state changes of phosphorus induced by proton irradiation were measured by a high-resolution wavelength-dispersive (WD) PIXE system. Six standard samples of phosphorus with different chemical states (Ca(H2PO4)2•H2O (P5+), CaHPO4•2H2O (P5+), NaH2PO4 (P5+), CaHPO3•H2O (P3+), Ca(H2PO2)2 (P1+), and NaH2PO2•H2O (P1+)) were prepared for the measurements. The P-Kα1 peak energy for the sample of P3+ increased after the irradiation. The peak energy of the P3+ sample became nearly same as that of P5+ after irradiation with more than 2 ×107Gy. This result indicates that P3+ in the sample has changed to P5+ due to proton irradiation. On the other hand, the P-Kα X-ray spectra for the samples of P5+ didn't show any interesting changes even for much higher proton dose (3.4 × 108Gy). Also, P-Kα peaks which correspond to chemical states (P5+ and P3-) other than original state were observed for the sample of P1+ in the region of more than 107Gy. [ABSTRACT FROM AUTHOR]