  Pulse shape discrimination with pure CsI scintillators is investigated as a
method for separating energy deposits by energetic neutrons and photons at
particle physics experiments. Using neutron data collected near the European
XFEL XS1 beam window the pulse shape discrimination capabilities of pure CsI
are studied and compared to CsI(Tl) using near-identical detector setups, which
were operated in parallel. The inelastic interactions of 100MeV neutrons are
observed to produce a slower scintillation emission in pure CsI relative to
energy deposits from cosmic muons. By employing a charge-ratio method for pulse
shape characterization, pulse shape discrimination with pure CsI is shown to be
effective for identifying energy deposits from neutrons vs. cosmic muons,
however, pure CsI was not able resolve the specific type of neutron inelastic
interactions as can be done with CsI(Tl). Using pulse shape discrimination, the
rate of energetic neutron interactions in a pure CsI detector is measured as a
function of time and shown to be correlated with the European XFEL beam power.
The results demonstrate that pulse shape discrimination with pure CsI has
significant potential to improve electromagnetic vs. hadronic shower
identification at future particle physics experiments.
