with collaborating scientific institutes in France (CESR Tolouse, CEA Saclay, CNES Toulouse), Germany (MPE Garching), Italy (INAF/IASF-Milano), Spain (University Valencia), Belgium (University Louvain), United Kingdom (University Birmingham), USA (UC San Diego, LBL Berkeley, NASA/GSFC Greenbelt). The spectrometer SPI performs spectral analysis of gamma-ray point sources and extended regions in the 20keV-8MeV energy range with an energy resolution of 2.2keV (FWHM) at 1.33MeV. This is accomplished with an array of 19 hexagonal high purity Germanium detectors cooled by a Stirling cooler system to an operating temperature of 85K. A hexagonal coded aperture mask is located 1.7m above the detection plane in order to image large regions of the sky (fully coded field of view is 16 degrees) with an angular resolution of 2 degrees. In order to reduce background radiation, the detector assembly is shielded by a veto (anticoincidence, ACS) system which extends around the bottom and sides of the detector almost completely up to the coded mask. The aperture (and hence contribution by cosmic diffuse radiation) is limited to 30 degrees. A plastic veto is provided below the mask to further reduce the 511keV background.
If you want to know more about SPI, we recommend that you start with the SPI Analysis User Manual [2].