  Roughly half of the observed gamma-ray bursts (GRBs) may arise from the
shocking of an ultra-relativistic shell of protons with the interstellar medium
(ISM). Any neutrons originally present in the GRB fireball may, depending on
the characteristics of the central engine, dynamically decouple as the fireball
accelerates. This leads to outflow consisting of separate fast proton and slow
neutron components. We derive detailed implications of neutron decoupling for
the observed lightcurves of short bursts. We show that the collision of a
neutron decayed shell with a decelerating outer shell is expected to result in
an observable second peak in the GRB lightcurve. There may be substantial
optical emission associated with such an event, so the upcoming Swift satellite
may be able to place constraints on models for short bursts. We also discuss
interesting inferences about central engine characteristics allowed by existing
BATSE data and a consideration of neutron decoupling.
