WINKLER: An imaging high resolution gamma-ray spectrometer

The WINKLER high-resolution gamma-ray spectrometer was originally developed to fly on a high-altitude aircraft. Following the discovery of Supernova 1987A in the Large Magellanic Cloud arrangements were made to perform balloon-borne observations of this event. The instrument was quickly adapted to fit on a gondola furnished by NASA/MSFC in a collaborative effort and was flown in a series of three successful flights from Alice Springs, Australia. The second flight on October 29-31, 1987 resulted in the first high-resolution detection of the 847-keV line emission from the decay of ⁵⁶Co and provided definitive confirmation of the explosive nucleosynthesis process. WlNKLER comprises an array of nine coaxial n-type germanium detectors which are housed in a common vacuum cryostat and surrounded by an NaI(Tl) scintillator shield that suppresses Compton interactions and gamma-ray background. Gamma-ray images are obtained with a rotational modulation collimator system attached to the spectrometer. Collimator holes in the upper section of the shield define the angular field of view of the instrument to 22° full width at half maximum. The energy range of the spectrometer is 20 eV to 8 MeV, and the composite energy resolution from all detectors is 1.5 keV at 100 keV and about 2.5 keV at 1.33 MeV