  The MIRAX X-ray observatory, the first Brazilian-led astrophysics space
mission, is designed to perform an unprecedented wide-field, wide-band hard
X-ray (5-200 keV) survey of Galactic X-ray transient sources. In the current
configuration, MIRAX will carry a set of four coded-mask telescopes with high
spatial resolution Cadmium Zinc Telluride (CZT) detector planes, each one
consisting of an array of 64 closely tiled CZT pixelated detectors. Taken
together, the four telescopes will have a total detection area of 959 cm^2, a
large field of view (60x60 degrees FWHM), high angular resolution for this
energy range (6 arcmin) and very good spectral resolution (~2 keV @ 60 keV). A
stratospheric balloon-borne prototype of one of the MIRAX telescopes has been
developed, tested and flown by the Harvard-Smithsonian Center for Astrophysics
(CfA) as part of the ProtoEXIST program. In this paper we show results of
validation and calibration tests with individual CZT detectors of the
ProtoEXIST second generation experiment (P2). Each one of 64 detector units of
the P2 detector plane consists of an ASIC, developed by Caltech for the NuSTAR
telescope, hybridized to a CZT crystal with 0.6 mm pixel size. The performance
of each detector was evaluated using radioactive sources in the laboratory. The
calibration results show that the P2 detectors have average energy resolution
of ~2.1 keV @ 60 keV and ~2.3 keV @ 122 keV. P2 was also successfully tested on
near-space environment on a balloon flight, demonstrating the detector unit
readiness for integration on a space mission telescope, as well as satisfying
all MIRAX mission requirements.
