Scattering of Slow Neutrons by Gaseous Methane

Slow neutron scattering by molecular gases is discussed. The most detailed comparison between theoretical and experimental results has been on gaseous methane which shows conclusively that the quantum nature of the rotational levels must be explicitly taken into account to obtain agreement with the experimental results. It is also shown theoretically that interference scattering, that is interference scattering between two distinct atoms of the molecule, has an effect which can be observed. This effect has been observed experimentally in methane and apparently also for propane. It is pointed out that the theory makes quite definite predictions at smaller momentum transfers than has been measured. Thus experiments at smaller momentum transfers are needed. (author)