| 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
neutron 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 either much closer together or further
apart. However, by doubling the separation distance between the 2 planes
from 20 cm to a distance of 40 cm we improved the angular resolution of
the detector from about 12.degree. to about 10.degree.. A further
doubling of the separation distance to 80 cm provided an addition
improvement in angular resolution of the detector to about 6.degree.
without adding additional detectors or 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,
therefore, is increased at the expanse of detection sensitivity. However,
the diminished sensitivity may be acceptable for those applications where
the detector is able to interrogate a particular site for an extended
period. |