Calibration and performance of the UCR double Compton gamma ray telescope

Results of the field calibration and performance of the UCR double Compton gamma-ray telescope are presented. The telescope is a balloon-borne instrument with an upper array of 16 plastic scintillator bars and a lower one of 16 NaI(Tl) bars. The telescope is sensitive to celestial gamma rays from 1 to 30 MeV. The data were collected on Feb. 14, 1988 prior to the launch in Alice Springs, Australia to observe SN 1987A. Radioactive sources were used to calibrate the energy deposits in the scintillators. Each bar was analyzed laterally using pulse height or timing to obtain the positions of the gamma ray interactions. Double scatter events from a ²⁴Na source simulating a celestial source were studied to obtain the general performance of the telescope and to develop imaging techniques, later used with the flight data. An angular resolution of 11° FWHM (full width at half maximum) and energy resolutions of 13% FWHM at 1.37 MeV and 10% FWHM at 2.75 MeV were found. The efficiency of the telescope is 3.5×10^-3 at an energy of 1.37 MeV and zenith angle of 31°. The magnetometer calibration gives the orientation of the detector with respect to the Earth to an accuracy of 0.5°