|
| | Neutrons are not emitted by most radionuclides that are
used for medical or industrial purposes.
 | Many legitimate sources of gamma-ray nuclides. |
| 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 neutron sources requires bulky moderators. |
| 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. |
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