Measurement of neutron emission from nuclear material, the emission being either spontaneous or induced by irradiation with neutron sources, in order to identify and measure the nuclear material. Detection of neutrons is normally accomplished by utilization of a neutron induced reaction (e.g. with 10B or 3He), resulting in the production of a charged particle which can be detected by its ionizing effect. In an application to verify irradiated fuel assemblies in storage pools, a 'fork detector system' is used that combines neutron counting with gamma ray detection.