A measurement of the change of the energy dependence of the total cross-section of phase II solid methane from confinement in aerogel glass

We report measurements of the energy dependence of the total neutron scattering cross-section of CH4CH4 both in bulk and confined in aerogel glass for neutron energies between ∼0.3and ∼200 meV. Solid CH4CH4 in phase II is an effective slow neutron moderation medium. Aerogel glass is one example of a broad class of disordered porous media with a large internal surface area. Many disordered materials possess excess low energy modes which have been seen in neutron scattering, and it is known that the confinement of materials inside porous media can produce modifications of the thermodynamic and excitation properties large enough to influence the neutron scattering cross-section. Our measurement shows that the confinement of the methane in pores of aerogel modifies the energy dependence total cross-section relative to bulk CH4CH4.