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Neutron interrogation techniques - differential die away
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  • 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 fissile material.
  • 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 initiate fission.
  • 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.
 

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