Imaging test setup for the coded-mask gamma-ray spectrometer SPI

The European Space Agency's International Gamma-Ray Astrophysics Laboratory (INTEGRAL) will be launched in 2002. One of its two main instruments is th e spectrometer SPI. It uses 19 HPGe detectors to observe the sky in the ene rgy range of 20 keV to 8 MeV with a resolution of DeltaE/E approximate to 0 .2%. Directional information is obtained using a coded mask. The expected a ngular resolution is about 2 degrees. The SPI imaging test setup (SPITS) wa s built at the Max-Planck-Institut fur Extraterrestische Physik, Germany, t o allow experimental verification of the imaging properties of SPI. SPITS c onsists of a coded hexagonal uniformly redundant array (HURA) mask and two germanium detectors. The mask is built from 63 opaque tungsten-alloy elemen ts. The two hexagonal Ge-detectors are housed in a common aluminum end cap. They are mounted on an XY-table and can be moved to cover the 19 SPI Ge-de tector positions. Mask and germanium detectors are made of SPI materials, w ith the exception of some Be parts, which have been replaced by thinner Al parts to allow experimental verification of the imaging properties of SPI. SPITS consists of a coded HURA mask and two germanium detectors. The mask i s built from 63 opaque tungsten-alloy elements. The two hexagonal Ge-detect ors are housed in a common aluminum end cap. They are mounted on an XY-tabl e and can be moved to cover the 19 SPI Ge-detector positions. Mask and germ anium detectors are made of SPI materials, with the exception of some Be pa rts, which have been replaced by thinner Al parts. The imaging properties o f SPITS are being measured with several radioactive sources at a distance o f 9 m from the detector plane. We obtain an angular resolution of about 2 d egrees at 1.8 MeV and a point-source location capability of SPITS of 15 arc min at 1.17 MeV.