SPI: A high resolution imaging spectrometer for INTEGRAL

SPI (Spectrometer for INTEGRAL) is a high spectral resolution gamma-ray telescope using cooled germanium detectors that will be flown on board the INTEGRAL mission in 2001. It consists of an array of 19 closely-packed germanium detectors surrounded by an active bismuth germanate (BGO) anti-coincidence shield. The instrument operates over the energy range 20 keV to 8 MeV with an energy resolution of 1–5 keV. A tungsten coded-aperture mask located 1.7 m from the detector array provides imaging over a 15° fully-coded field-of-view with an angular resolution of ∼3°. The point source narrow-line sensitivity is estimated to be 3–7×10−6 ph cm−2 s−1 over most of the range of the instrument (E>200 keV) for a 106 s observation. With its combination of high sensitivity, high spectral resolution and imaging, SPI will improve significantly over the performance of previous instruments such as HEAO-3, OSSE, and Comptel. It can be expected to take a major step forward in experimental studies in nuclear astrophysics. The ...