Studies on potential moderator materials for very cold neutron sources

Abstract

The increasing demand for long wavelength neutrons is being motivated by the need to study larger objects and slower motions characterizing the new materials related to the requirements of nowadays science and technology. However, not much work has been done so far towards the identification of materials and conditions able to produce a copious flux of very cold neutrons (VCN) at either stationary or pulsed sources. This work presents the results of a preliminary study aimed at exploring materials that look promising as potential moderators for VCN sources. For this purpose, a search is done for the existence of very low energy excitations in the generalized density of states of some molecular systems, which can be efficient to slow down already cold neutrons by exchanging energy with them. Besides reviewing and improving the available information on methane (II) and methane clathrate, it is found that such objective can be realized by the quantum dynamics corresponding to the librations of the methyl groups in the methyl fluoride and the p-xylene molecules encapsulated in two different molecular hosts at low temperatures.