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Space-station Observer for Nuclear Gamma-ray Spectroscopy (SONGS) was proposed to NASA for the Space Station Attached Payloads Program. The instrument comprises an array of 19 two-segment, n-type Ge detectors providing high energy resolution with a total sensor area of 373 cm2. A rotational modulation collimator imaging system which can be deployed in and out of the nominal 15°F0V, provides a spatial resolution of 1.2°. Energy resolution of 1 keV at 100 keV and 2 keV at 1 MeV permits definitive identification of line spectra resulting from high energy processes at work in the cosmos. The 36 sensitivities limits of (3-8)106 photons/(cm2 s) are achieved for lines between 100 keV and 1-2 MeV, and a few times 10-7 photons/(cm2 s keV) for the continuum flux with exposure periods of 106 s. In addition, the close-packed Ge sensor array provides a natural sensitivity for the measurement of gamma ray polarization in the 100 keV to 1 MeV energy range. Such polarization data should yield important information relating to the structure of the magnetosphere of neutron stars and of the accretion disk of black holes. The entire instrument will be mounted on a two-axis pointing system with the capability to fix on a target source independent of the Space Station orientation. A quick response for the pointer will allow observations of transient events. A massive (-270 kg), multi-segmented, NaI shield surrounding the Ge detectors is designed to recognize a gamma-ray burst or a solar flare event and to determine its source direction to about 2-3° which is precise enough to direct the pointer well within the 15° FOY of the Ge detectors. The SONGS spectrometer is a derivative of the Advanced Nuclear Gamma-ray Analysis System (ANGAS), the design of which is essentially complete and ready for production. The Space Station is an ideal platform to perform gamma-ray astronomy since it accommodates large payloads, permits long term observations, and orbits in a relatively low background environment by virtue of its low altitude and low inclination angle.
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