- Neutron interrogation is one way of measuring quantities of fissile
material and is useful for rapid and routine measurement.
- The sample (1 m diameter drum) is irradiated by a pulse of fast
neutrons from a neutron generator. These fission neutrons are
moderated, scattered into the sample and stimulate fission in any
- Fast neutrons released by fission are detected by cadmium shielded 3He
detectors which are placed in polyethylene around the sample
positions. Thermalised neutrons then scatter into the sample and
- The initial interrogating pulse will not have disappeared by time C,
but the newly born fission neutrons die away over a longer time scale
of a couple of milliseconds. Thus by counting fast response neutrons
in the time slot C - D we obtain a signal that is proportional to the
quantity of fissile material present.