Among the pulsed white spectrum neutron sources available in the world, the
linear electron accelerator facility at IRMM (GELINA) is the one with the best
time resolution. GELINA combines four specially designed and distinct units: a
high-power pulsed linear electron accelerator, a post-accelerating beam
compression magnet system, a mercury-cooled uranium target, and very long
flight paths.
The GELINA neutron source is based on a linear electron accelerator producing
electron beams. A typical beam operation mode uses 100 MeV average energy, 10
ns pulse length, 800 Hz repetition rate, 12 A peak and 100 µA average current.
With a post-acceleration pulse compression system, the electron pulse width
can be reduced to approximately 1 ns (FWHM) while preserving the current,
resulting in a peak current of 120 A. The accelerated electrons produce
Bremsstrahlung in an uranium target which in turn, by photonuclear reactions,
produces neutrons. Within a 1 ns pulse a peak neutron production of 4.3 x 10
10 neutrons is achieved (average flux of 3.4 x 1013
neutrons/s).
The neutron energy distribution emitted by the target ranges from subthermal
to about 20 MeV, with a peak at 1-2 MeV. To have a significant number of
neutrons in the energy range below 100 keV, a hydrogen-rich moderator is
added. The partially moderated neutrons have an approximate 1/E energy
dependence plus a Maxwellian peak at thermal energy. By using collimators and
shadow bars moderated or unmoderated neutron beams are selected for the twelve
neutron flight paths. Further tailoring of the spectral shape is done with
movable filters.
The up to 400 m long flight paths, symmetrically arranged around the uranium
target, lead to experimental locations at distances of 10, 30, 50, 60, 100,
200, 300 and 400 m. These experimental stations are equipped with a variety of
sophisticated detectors, and data acquisition and analysis systems. GELINA is
a multi-user facility serving up to 12 different experiments simultaneously.
The facility is operated in shift work on a 24 hours/day basis, for about 100
hours per week.
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Linear electron accelerator
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Beam compression magnet
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Flight paths
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Neutron flux
Energy resolution