Performance of the prototype LANL solid deuterium ultra-cold neutron source

A prototype of a solid deuterium (SD2) source of Ultra-Cold Neutrons (UCN) is currently being tested at LANSCE. The source is contained within an assembly consisting of a 4 K polyethylene moderator surrounded by a 77 K beryllium flux trap in which is embedded a spallation target. Time-of-flight measurements have been made of the cold neutron spectrum emerging directly from the flux trap assembly. A comparison is presented of these measurements with results of Monte Carlo (LAHET/MCNP) calculations of the cold neutron fluxes produced in the prototype assembly by a beam of 800 MeV protons incident on the tungsten target. A UCN detector was coupled to the assembly through a guide system with a critical velocity of 8 m/s (58Ni). The rates and time-of-flight data from this detector are compared with calculated values. Measurements of UCN production as a function of SD2 volume (thickness) are compared with predicted values. The dependence of UCN production on SD2 temperature and proton beam intensity are also presented.