  We use Hubble Space Telescope (HST) imaging from the ACS Treasury Survey to
determine fits for single population isochrones of 69 Galactic globular
clusters. Using robust Bayesian analysis techniques, we simultaneously
determine ages, distances, absorptions, and helium values for each cluster
under the scenario of a "single" stellar population on model grids with solar
ratio heavy element abundances. The set of cluster parameters is determined in
a consistent and reproducible manner for all clusters using the Bayesian
analysis suite BASE-9. Our results are used to re-visit the age-metallicity
relation. We find correlations with helium and several other parameters such as
metallicity, binary fraction, and proxies for cluster mass. The helium
abundances of the clusters are also considered in the context of CNO abundances
and the multiple population scenario.
