  PoGOLino is a scintillator-based neutron detector. Its main purpose is to
provide data on the neutron flux in the upper stratosphere at high latitudes at
thermal and nonthermal energies for the PoGOLite instrument. PoGOLite is a
balloon borne hard X-ray polarimeter for which the main source of background
stems from high energy neutrons. No measurements of the neutron environment for
the planned flight latitude and altitude exist. Furthermore this neutron
environment changes with altitude, latitude and solar activity, three variables
that will vary throughout the PoGOLite flight. PoGOLino was developed to study
the neutron environment and the influences from these three variables upon it.
PoGOLino consists of two Europium doped Lithium Calcium Aluminium Fluoride
(Eu:LiCAF) scintillators, each of which is sandwiched between 2 Bismuth
Germanium Oxide (BGO) scintillating crystals, which serve to veto signals
produced by gamma-rays and charged particles. This allows the neutron flux to
be measured even in high radiation environments. Measurements of neutrons in
two separate energy bands are achieved by placing one LiCAF detector inside a
moderating polyethylene shield while the second detector remains unshielded.
The PoGOLino instrument was launched on March 20th 2013 from the Esrange Space
Center in Northern Sweden to an altitude of 30.9 km. A description of the
detector design and read-out system is presented. A detailed set of simulations
of the atmospheric neutron environment performed using both PLANETOCOSMICS and
Geant4 will also be described. The comparison of the neutron flux measured
during flight to predictions based on these simulations will be presented and
the consequences for the PoGOLite background will be discussed.
