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Why Neutrons

Neutrons are not emitted by most radionuclides that are used for medical or industrial purposes.

  • Radiophamaceuticals and industrial radionuclides will set off gamma sensitive alarms. No legitimate reason to possess neutron source
  • Detecting neutrons is usually unambiguous and indicates the presence of special nuclear materials.

VERY difficult to shield

  • Shielding can even enhance the detection probability by increasing the thermalization and therefore the detection efficiency for thermal neutrons.

Neutron background is small and constant

  • Neutron background rates throughout the world are remarkably constant.
  • They vary from 0.007 n/cm2/sec at sea level to 0.014 n/cm2/sec near facilities like the Hanford Reservation in Washington State.
  • These background rates are quite low compared to the expected count rates from small masses of metallic, oxide or weapons grade Pu.

Low false-alarm rate

  • False positives are not acceptable when freight and people must be stopped and inspected when an alarm goes off.