Optical-phonon structure and precision neutron total cross section measurements of zirconium hydride

Abstract

Precision total neutron cross section measurements of ZrH1.58 were performed using a highly monochromatic neutron beam for neutron energies between 0.035 and 1.1 eV. The experimental values of the cross section in the region of the one-phonon optical peak (0.100 eV<En<0.250 eV) compare well with calculations if one assumes that the phonon spectrum g( epsilon ), is represented by three Gaussians centred at 0.132, 0.137 and 0.151 eV, with associated widths of 0.05, 0.02 and 0.01 eV, respectively. The phonon spectrum g( epsilon ) departs from the calculations as exemplified by the central force (CF) model of ZrH2. Such departures may arise due to non-central forces and tetragonality. The structure of g( epsilon ) in some respects is similar to that observed in inelastic neutron scattering cross section measurements. The results from these two independent and different types of measurements provide sufficient basis for further attempts toward a more realistic theoretical model of ZrH2.