Abstract. SPI is a high spectral resolution gamma-ray telescope on board the ESA mission INTEGRAL (International Gamma Ray Astrophysics Laboratory). It consists of an array of 19 closely packed germanium detectors surrounded by an active anticoincidence shield of BGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16• , the partially coded field of view amounts to 31• , and the angular resolution is 2.5• . The energy range extends from 20 keV to 8 MeV with a typical energy resolution of 2.5 keV at 1.3 MeV. Here we present the general concept of the instrument followed by a brief description of each of the main subsystems. INTEGRAL was successfully launched in October 2002 and SPI is functioning extremely well.

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International audienceWe investigated the direction distribution of protons around 20 km of altitude by mean of stratospheric balloons. Our detection instrument was based on two large silicon diodes, which were differently tilted. Our measurements show that the proton flux is not isotropic and that protons have a higher probability to have a direction near the vertical axis than near the horizontal axis which proved the proton flux anisotropy. By simulation we then determined an empirical expression for the angular differential fluence of protons