The Ludlum Model 42-30H Neutron Detector is designed for detection of thermal and fast neutrons (0.025 eV to approximately 12 MeV). The neutrons are detected, not directly, but through nuclear reactions, which result in energetic charged particles such as protons and tritons. In many instances, intense fields of gamma rays are also found with neutrons. Therefore, it is important to choose a method of neutron detection with the ability to discriminate against these gamma rays in the detection process.
A common reaction for the conversion of slow neutrons into directly detectable particles is n + 3He → 3H + 1H + 0.764 MeV. The Ludlum Model 42-30H utilizes this reaction in the form of helium-3 (³He), which fills the gas proportional tube of the detector.
The Model 42-30H is typically used with area monitors. To detect neutrons with energies above the thermal region, the detector is placed inside the moderator. The detector can be removed from the moderator for the detection of thermal neutrons.
