Ludlum Model 42-30H Neutron Detector
The Model 42-30H is a neutron detector designed for detection of
thermal and fast neutrons. Typically used with a Model 375 Area Monitor.
The neutron “remball” detector has been the
standard for measuring neutron fields for more
than 50 years. Recently, the Department of
Transportation (DOT) and International Air
Transport Association (IATA) regulations have
cracked down on the shipping of these detectors
due to the poisonous nature of the BF3. The
Model 42-30H eliminates this problem with the
introduction of the 3He tube.
The differences and similarities between BF3
and 3HE tubes are:
Energy Response: There is no change in
energy response which still follows the inverse-
Crosstalk: Gamma interference or “crosstalk”
is the same for both the BF3 and 3He tubes.
Crosstalk is less than 10 counts per minute at
High Voltage: Operating HV is normally about
1100 Vdc for the 3He tube, where the BF3 tube
required about 1700 Vdc.
Count Rate: The 3He tube has approximately
four times the count rate of the BF3 tube at a
given neutron dose rate. This difference is
mostly beneficial because it reduces statistical
Pressure: The 3He tubes have less than 2.7
atmospheres of pressure and are exempt from
any shipping requirements.
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