Chemistry of proton track registration in cellulose nitrate polymers

Changes in the intensities of the functional groups within the surface region (upper 500 nm) of cellulose nitrate films, exposed to 0.5 MeV protons and processed chemically to visualize proton tracks, have been determined quantitatively by attenuated total reflectance (ATR) infrared spectrometry. Within the penetration depth of protons resulting from the thermal neutron reaction, 14N(n, p)14C at a neutron fluence of 2×1011, absorption intensities of nitrate (-ONO2) and ether (-C-O-C-) are depleted by up to 37% and 12% at respective characteristic vibrational frequencies. The observed cleavage of the ether linkages (C-O-C at 1060 cm−1) in the main cellulose chain creates lower molecular weight polymer fragments, and also causes depolymerization. Both reactions increase the accessibility of the polymer to chemical attack by the NaOH etchant at the chemically altered sites. The unique track registration of low energy protons (0.5-0.3 MeV) in cellulose nitrate primarily results from selective chemical induced damage from energy deposition interactions at bonded nitrate group sites.