  We present measurements of X-ray Parametric Down Conversion at the Advanced
Photon Source synchrotron facility. Using an incoming pump beam at 22 keV, we
observe the simultaneous, elastic emission of down-converted photon pairs
generated in a diamond crystal. The pairs are detected using high count rate
silicon drift detectors with low noise. Production by down-conversion is
confirmed by measuring time-energy correlations in the detector signal, where
photon pairs within an energy window ranging from 10 to 12 keV are only
observed at short time differences. By systematically varying the crystal
misalignment and detector positions, we obtain results that are consistent with
the constant total of the down-converted signal. Our maximum rate of observed
pairs was 130 /hour, corresponding to a conversion efficiency for the
down-conversion process of $5.3 \pm 0.5 \times 10^{-13}$.
