| Abstract: | An instrument that will directly image the fast fission neutrons from a
special nuclear material source wherein the neutron detection efficiency
is increased has been described. Instead of the previous technique that
uses a time-of-flight (TOF) between 2 widely spaced fixed planes of
detectors to measure scatter neutron kinetic energy, we now use the
recoil proton energy deposited in the second of the 2 scatter planes
which can now be repositioned much closer together. Allowing the 2 planes
to be placed closer together has been shown to provide up to about a
.about.170% improvement in detection efficiency without adding additional
detectors and ancillary electronics. The distance between planes also may
be dynamically changed using a suitable common technique such as a gear-
or motor-drive to toggle between the various positions. The angular
resolution of this new configuration is diminished but this loss of
resolution may be acceptable for those applications where only modest
directionality is sufficient to identify a threat. |