  A new technique for detection of slow neutrons with gaseous detectors using
ultra-thin layers with 10B atoms is presented. The reaction between a thermal
neutron and a 10B atom releases 2 secondary particles, namely a 7Li ion and an
alpha particle, which due to momentum conservation are emitted in opposite
directions, along the same line (back to back). Current boron coated neutron
detectors are equipped with 10B films with thicknesses of several micrometers,
deposited on very thick substrate plates. However, since the ranges of the 7Li
ion and the alpha particle are of few micrometeres in most materials, one of
these particles is always lost in the 10B layer or substrate. As such, these
detectors lose the ability to reconstruct the reaction line of action and to
precisely determine the neutron position, as only one of the two secondary
particles track can be measured. With the technique now presented, the sum of
the 10B layer and the substrate thicknesses is small enough to allow for both
secondary particles to escape and ionize the gas in opposite sides of the 10B
converter foil. Independent readout structures, one on each side of the 10B
converter foil, detect each secondary particle and determine its track centroid
and the deposited energy. Since the two secondary particles are emitted back to
back, the neutron position can be obtained by combining the information
recorded by the two readout structures. Through GEANT4 simulations, we verified
that the spatial resolution can be significantly improved: our results show
that, by using a B4C layer with a thickness of 1 micron on a 0.9 micron Mylar
substrate, the spatial resolution can by improved by a factor of 8, compared to
conventional detectors with thick 10B detection layers.
