  We model the X-rays reprocessed by an accretion disk in a fiducial low-mass
X-ray binary system with a neutron star primary. An atmosphere, or the
intermediate region between the optically thick disk and a Compton-temperature
corona, is photoionized by the neutron star continuum. X-ray lines from the
recombination of electrons with ions dominate the atmosphere emission and
should be observable with the Chandra and XMM-Newton high-resolution
spectrometers. The self-consistent disk geometry agrees well with optical
observations of these systems, with the atmosphere shielding the companion from
the neutron star. At a critical depth range, the disk gas has one thermally
unstable and two stable solutions. A clear difference between the model spectra
exists between evaporating and condensing disk atmospheres. This difference
should be observable in high-inclination X-ray binaries, or whenever the
central continuum is blocked by absorbing material and the extended disk
emission is not.
