Design of a cold neutron source

This paper concerns the optimization of a cold neutron source that will be part of an ultra-low-background facility for basic and applied neutron beam research under construction at the Cornell 500-kW TRIGA reactor. The principal features of the design are summarized. To obtain a nearly pure subthermal beam with few fast neutrons or gamma rays, a 13-m-long 500-m-radius curved 2- x 5-cm neutron guide is to be used as a filter. To eliminate interference from other experiments, the exit of the guide will be in its own shielded room. To increase the transmitted intensity, neutrons entering the guide will be cooled to ∼40K by a cold moderator in a beam port in the reactor reflector. To avoid potential hazards associated with liquid H2 or solid CH4 (the usual cold moderators), mesitylene, a liquid at room temperature, has been chosen. To simplify operation and to avoid circulating cryogenic fluids inside the beam port, cooling of the mesitylene will be by copper cold fingers connected to a cryogenic refrigerator outside the reactor shield