Model42-49 NeutronDetector TechnicalManual Section1
Ludlum Measurements, Inc. Page 1-1 December 2017
Introduction
he Ludlum Model 42-49 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 energetically charged particles such as
alpha particles. 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 42-49 utilizes this reaction in the form of helium-3(3He),
which fills the gas proportional tube of the detector
The Model 42-49 is designed to be used with portable counting instruments
and has a top bracket that allows for convenient mounting of a portable
instrument. (See picture below.) The Model 42-49 consists of a 3He detector
(1.6 cm diameter x 2.5 cm thick), surrounded by a high density polyethylene
sphere, 19.6 cm (7.7 inches) in diameter. This outer sphere moderates the
incoming neutrons and helps provide a near-rem response.
Model 42-49 Detector shown as part of a Model 30-7
