An ultracold neutron source at the NC State University PULSTAR reactor

Research and development is being completed for an ultracold neutron (UCN) source to be installed at the PULSTAR reactor on the campus of North Carolina State University. The objective is to establish a university-based UCN facility with sufficient UCN intensity to allow world-class fundamental and applied research with UCN. To maximize the UCN yield, a solid ortho-D2 converter will be implemented coupled to two moderators, D2O at room temperature, to thermalize reactor neutrons, and solid CH4, to moderate the thermal neutrons to cold-neutron energies. The source assembly will be located in a tank of D2O in the space previously occupied by the thermal column of the PULSTAR reactor. Neutrons leaving a bare face of the reactor core enter the D2O tank through a 45 x 45 cm cross-sectional area void between the reactor core and the D2O tank. Liquid He will cool the disk-shaped UCN converter to below 5 K. Independently, He gas will cool the cup-shaped CH4 cold-neutron moderator to an optimum temperature between 20 K and 40 K. The UCN will be transported from the converter to experiments by a guide with an inside diameter of 16 cm. Research areas being considered for the PULSTAR UCN source include time-reversal violation in neutron beta decay, neutron lifetime determination, support measurements for a neutron electric-dipole-moment search, and nano-science applications. © 2001 Elsevier Science. All rights reserved