Fissile neutron detector

A fissile neutron detection system for detecting incident fissile neutrons, said fissile neutron detection system, comprising:

• an ionizing thermal neutron detector arrangement defining an inner peripheral shape that at least substantially surrounds a moderator region for detecting thermal neutrons that exit the moderator region but the incident fissile neutrons at least generally pass through the ionizing thermal neutron arrangement;
• and
• a moderator arrangement disposed within the moderator region for converting the incident fissile neutrons in the moderator region to thermal neutrons which exit the moderator region to then enter the thermal neutron detector arrangement for detection of at least some of the thermal neutrons to produce an electrical signal as a detector output with the moderator arrangement having an outer peripheral shape that is at least generally complementary to said inner peripheral shape and the moderator arrangement includes lateral extents such that any given dimension that bisects the lateral extents includes a length that is greater than any thickness of the moderator arrangement transverse to the lateral extents.