Neutronic Measurements on Ammonia for Neutron Moderation

At many neutron sources today, only one part per billion of the neutrons generated at a source will reach a measurement device within a useful energy band, which leaves plenty of room for improvement in this area of research. The Low Energy Neutron Source (LENS) at Indiana University’s Center for Exploration of Energy and Matter (CEEM) has made multiple contributions to neutron scattering community, with an emphasis on improving neutron instrumentation. One of the efforts that is made at LENS is the analysis of potential neutron moderators for producing larger amounts of cold and thermal neutrons. We have chosen for our experiments to be focused on Ammonia (NH₃), which is intriguing to LENS due to its high Hydrogen content, its molecular mass, and its broad, accessible temperature range. For our experiments, we require a cryostat capable of bringing Ammonia to a condensed state (Approx. 220 K) and control the temperature for long periods of time. Here, we present the effectiveness of our cryostat design in terms of accurate temperature control, as well as the results of neutron transmission measurements on Ammonia to determine its total neutron cross section, for neutrons with energies of 0.1 meV – 1 eV.