  The ComPair gamma-ray telescope is a technology demonstrator for a future
gamma-ray telescope called the All-sky Medium Energy Gamma-ray Observatory
(AMEGO). The instrument is composed of four subsystems, a double-sided silicon
strip detector, a virtual Frisch grid CdZnTe calorimeter, a CsI:Tl based
calorimeter, and an anti-coincidence detector (ACD). The CsI calorimeter's goal
is to measure the position and energy deposited from high-energy events. To
demonstrate the technological readiness, the calorimeter has flown onboard a
NASA scientific balloon as part of the GRAPE-ComPair mission and accumulated
around 3 hours of float time at an altitude of 40 km. During the flight, the
CsI calorimeter observed background radiation, Regener-Pfotzer Maximum, and
several gamma-ray activation lines originating from aluminum.
