“…After Butterworth et al built the first cold neutron device in a nuclear reactor (BEPO at Harwell, UK) in 1957 [1,2] cold neutron sources were incorporated into the design of both nuclear reactor-based, steady-state neutron sources (including the use of liquid hydrogen isotopes) [3,4] and of pulsed neutron sources [5]. High brightness (neutron flux per unit solid angle) cold neutron sources using liquid deuterium were very successfully implemented at the Institut Laue-Langevin in the 1970s and 1980s [6,7], with similar concepts at the FRM-II, Technische Universität München, Garching, Germany [8] and the Opal Reactor in Australia [9]. More compact cold sources, using liquid hydrogen, have been successfully operated at the Orphée reactor, France, the HFIR reactor at Oak Ridge National Laboratory, USA, and here at the NIST Center for Neutron Research (NCNR).…”