Dynamical features of methane hydrate around 12 K

Methane hydrate is a possible candidate material for use as a cold neutron moderator in pulsed neutron sources. Our aim was to perform inelastic neutron scattering measurements with sufficient range in energy and momentum to create a scattering kernel to simulate its behavior as a moderator material. Measurements were made on samples of D2O-CH4 and H2O-CH4 at 12 K covering a range up to 500 meV and 28 A-1. These data clearly shows the almost free recoil of the CH4 rotational and vibrational modes and confirms that the dynamics of the ice and methane are largely decoupled on the energy scales that we are studying. From these initial measurements we can conclude that methane hydrate will be a good moderator over a wide range of neutron energies. We are now able to produce models of sufficient quality to create scattering kernels for the Monte-Carlo simulation codes that are used to design neutron sources