Re-entrant cones for moderator chamber of a neutron imaging system

A neutron imaging system that includes a central neutron source configured to produce source neutrons, wherein the central neutron source comprises a beam target, a moderator chamber surrounding at least a portion of the beam target, the moderator chamber housing a moderator, and a re-entrant cone extending into the moderator chamber. The re-entrant cone includes an entrance surface facing the beam target. The entrance surface encloses a cone chamber, isolating the cone chamber from the moderator. Furthermore, the entrance surface is shaped such that source neutrons produced at the beam target impinge the entrance surface with a neutron flux that varies by 10% or less along the entrance surface.