Some concluding remarks about cold moderator development

This is the transcription of remarks made at the conclusion of the Workshop, including some questions that emerged, some suggestions that arose and some general observations. Scientists need inelastic scattering data for cryogenic moderator materials to enable calculations of moderator performance and thus to support informed design decision and interpretation of measurements. Ideally, the data would be in the form of the full scattering law S(Q,ω), represented is some format appropriate for input to Monte Carlo and other neutron transport codes. The functions must accurately represent the temperature dependence of the scattering, and account properly for the possibility of thermodynamic non-equilibrium of the medium (as for example in cold ortho-para H2.) Of course descriptions of the scattering from some candidate moderator materials already exist at some level of approximation. Cryogenic moderator performance depends sensitively on the internal molecular vibrational motions, the free-or-nearly-free molecular rotational motions, and on the center of mass motions. Broadly speaking these are respectively in the ranges of tens to hundreds of millivolts, few millivolts and few-to-submillivolts. Measurements performed to support the development of scattering laws require different instruments to address these different energy transfer ranges. In a real sense, the effort is one of boostrapping, using existing neutron facilities to provide data needed to improve the neutron sources. It should be easy now, using existing instruments for example on the pulsed sources, chopper spectrometers for the high energy transfer ranges and crystal analyzer instruments for the low energy transfer ranges