  We present observations of the X-ray halo around the LMXB GX 13+1 from the
Chandra X-ray telescope. The halo is caused by scattering in interstellar dust
grains, and we use it to diagnose the line-of-sight position, size
distribution, and density of the grains. Using the intrinsic energy resolution
of Chandra's ACIS CCDs and the recent calibration observation of the Chandra
point spread function (PSF), we were able to extract the halo fraction as a
function of energy and off-axis angle. We define a new quantity, the ``halo
coefficient,'' or the total halo intensity relative to the source at 1 keV, and
measure it to be $1.5^{+0.5}_{-0.1}$ for GX 13+1. We find a relationship
between this value and the dust size, density, and hydrogen column density
along the line of sight to GX 13+1. We also conclude that our data does not
agree with ``fluffy'' dust models that earlier X-ray halo observations have
supported, and that models including an additional large dust grain population
are not supported by these data.
