Design and construction of a cold neutron source for use in the Cornell University TRIGA reactor

A cold neutron source has been designed and constructed for insertion into the 6''-radial beam port of the Cornell University TRIGA reactor for use with a neutron guide tube system. The main differences between this cold source and other existing sources are the use of heat conduction as the method of cooling and the use of mesitylene (1,3,5-trimethylbenzene; melting point, 2280K; boiling point, 4370K) as the moderating material. This thesis describes the design and construction details of the cold neutron source, discusses its safety aspects, and presents its cryogenic performance curves and also the results of a test of its neutron moderating ability. To test the neutron moderating ability of the cold neutron source, an out-of-reactor neutron transmission experiment was performed with the moderator chamber first at room temperature and then at about 230K. The results indicate that the neutron energy spectrum is strongly shifted to lower energies when the chamber is cold. The neutrons have an apparent temperature of 980K, if the moderated flux is assumed to be Maxwellian. This, however, is unlikely to be the actual case since the geometry of the chamber, neutron beam, and detector and the complexities of the neutron scattering and absorption processes in mesitylene doubtlessly distort the leakage energy spectrum