Design Features of a Prototype Neutron Portal Monitor

Design considerations are presented which lead to the construction of a very large neutron detector with a high neutron detection efficiency and extreme insensitivity to gamma-ray backgrounds. Such a detector is a possible substitute for the present helium-3 neutron portal monitor. These detectors are deployed at international border crossings and in radiation surveillance vehicles at shipping ports in the USA. However helium-3 gas is becoming scarce and expensive so an alternate neutron detection technology is being sought.