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

ESA´s INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) will be launched in 2002. One of its two main instruments is the spectrometer SPI. It uses 19 HPGe detectors to observe the sky in the energy range of 20 keV to 8 MeV with a resolution of ΔE/E=0.2%. Directional information is obtained using a coded mask. The expected angular resolution is about 2°. The SPI Imaging Test Setup (SPITS) was built at MPE to allow experimental verification of the imaging properties of SPI. SPITS consists of a coded HURAmask and two germanium detectors. The mask is built from 63 opaque tungsten-alloy elements. 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-detector positions. Mask and germanium detectors are made of SPI materials, with the exception of some Be parts which have been replaced by thinner Al parts. The imaging properties of SPITS are being measured with several radioactive sources-at a distance of 9 m from the detector plane. The authors obtain an angular resolution of about 2° at 1.8 MeV and a point-source location capability of SPITS of 15 arcmin at 1.17 MeV. Two-sources whose signal/background ratio is 2.7 are reconstructed correctly at 40 significance level