The use of drift chambers in a telescope for high energy gamma-ray astronomy

The design of a high energy (greater than 100 MeV) gamma-ray telescope using drift chambers has been investigated. Apart from improved spatial resolution compared with conventional spark chambers, drift chambers offer a number of useful advantages, which make them suitable for the next generation of gamma-ray instruments. A gamma-ray telescope using 0.5 m x 0.5 m prototype drift chambers has been assembled and tested using electron and tagged gamma-ray beams. The spatial resolution is 180 microns and angular resolution (1 standard deviation projected) for 155 MeV gamma-rays is 1.4. These results represent a notable improvement over previous instruments flown in space, such as SAS-2 and COS-B. Various design improvements are discussed which would permit further improvement in this performance, making drift chambers worthy of serious consideration for future gamma-ray missions.