Recent measurements with a balloon borne Ge(Li) spectrometer in gamma-ray astronomy

A new high resolution γ-ray spectrometer for astrophysical measurements has been jointly developed at Saclay and Toulouse. The instrument consists of a large Ge(Li) crystal (140 cm3) cooled to liquid nitrogen temperature and actively shielded by a sodium iodide crystal. Spectral resolution and effective area, are respectively 3.0 keV (fwhm) and 2.7 cm2 at 1 MeV. Three flights were carried out in Brazil (Dec. 76, Feb. 77) with a stabilized gondola. The total background counting rate was about 10 counts/s in the 0.1-8 MeV energy range at float altitude (2.9 g cm-2 residual atmosphere, 12 GV rigidity cutoff). The sensitivity of the detector is about 10-3 photons cm-2 s-1 over the above energy range for three hours of observation of a point source. Preliminary results are described. (Auth.)