  This paper reports on successful growth and performance evaluation of two
large diameter Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (CHCB), both recently developed
scintillator crystals. The discovery of Cs2HfCl6 (CHC) as a scintillator has
lately generated much interest in this material and its family, which belongs
to the K2PtCl6 cubic crystal structure. CHC is an intrinsic scintillator that
is non-hygroscopic, has no self-radioactivity, provides excellent energy
resolution, and has excellent non-proportionality. CHC has a moderate density
of 3.9 g/cm3 and an effective atomic number of 58. Reported in this paper are
transparent crack-free single crystal CHC and CHCB boules of one inch in
diameter, both grown using the vertical Bridgman method. Samples retrieved from
the boules, sized 23mm dia. x 30mm and 23mm dia. x 26mm, respectively, are
characterized for their optical and scintillation properties. Energy
resolutions of 3.5% and 3.7% (FWHM) at 662 keV, respectively, are reported.
Results comparable to previously reported results for smaller crystals have
been obtained. Studies on light yield, decay time, non-proportionality, as well
as detector characterization are also reported.
