Incoherent inelastic neutron scattering measurements on dome-fuji antarctic ice

We measured the incoherent inelastic neutron scattering (IINS) in ice (depth, 201–2201 m) recovered from Dome-Fuji (DF), Antarctica. We found that the peak intensity of librational vibration in the IINS spectra of DF ice changes with the ice temperature (Ti) in the ice sheet: the intensity at 97 meV decreases with increases in depth from 201 to 2201 m. From the IINS spectra, we calculated the Ti dependence of the order parameter (the ratio of ordered protons in ice), which is consistent with the theory of the order-disorder phase-transition from proton arrangements in ordinary ice to proton-ordered arrangements at Ti = 237 K. The results indicate that Antarctic ice in which Ti ≤ 237 K contains proton-ordered arrangements.