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 can¿t 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. The technology for producing and transporting methane pellets has been demonstrated in previous SBIRs. This effort will validate the neutron performance of such a moderator. Sample moderators filled with polyethylene pellets similar to the solid methane pellets were prepared and studied at the IUCF LENS facility. Packing densities of over 60% were achieved. In addition the phase II apparatus was designed and a preliminary safety analysis made. Initial work was done on assembling the Phase II apparatus into a mobile cart. The phase II solid methane pelletizer will be completed and delivered and installed on the LENS facility at Indiana University. Neutron scattering and transmission experiments will be made on solid methane pellet filled cryogenic moderators to determine the effects of packing densities and non-uniformities on the neutron beam. Commercial Applications and other Benefits as described by the awardee: The proposed research will develop and validate the cryogenic pellet technologies required to implement pellet moderators on advanced cold and very cold neutron sources. 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 capabilities of the neutron facilities