Development and Neutronic Validation of Pelletized Cold and Very Cold Moderators for Pulsed Neutron Sources

Existing and planned neutron facilities, such as the Spallation Neutron Source, generate bursts of cold neutrons for materials research. The efficiency of the beam line components, which convert the fast neutrons to a cold neutron beam, determines the usefulness of the facility. Existing solid methane moderators have a high efficiency, but cannot be scaled to work on high power facilities. A cold moderator using solid methane pellets would be capable of operating on a high power pulsed neutron source. In previous work, the technology for producing and transporting methane pellets has been demonstrated. This project will validate the neutron performance of such a moderator. In Phase I, neutron scattering and transmission on mock moderators, consisting of various random packings of polyethylene pellets, will be performed to obtain preliminary data on the effects of packing densities and non-uniformities on the neutron beam. Commercial Applications and other Benefits as described by the awardee: A methane pellet moderator would double the output of cold neutrons compared to a conventional hydrogen moderator. The improved performance would further the materials research capability of neutron facilities