A high performance anticoincidence rejection system for balloon borne MWPC

The supernova SN 1987A has been observed in the range of hard X-rays (15-180 keV) and high-energy gamma -rays (50-500 MeV) with a payload launched from the balloon facility of Alice Springs (Australia) during April 1987 and 1988. The low-energy detector based on a MWPC had a sensitive area of 500 cm/sup 2/. In the second flight a complete plastic shield was added for the first time to the multiwire proportional counter (MWPC). By switching on the active shield, the background counting rate dropped from 4.2 to 2.8*10/sup -4/ counts/cm/sup 2/-s-keV with no change in the deadtime of the counter. It is concluded that the use of a multitechnique rejection system for this kind of gaseous detector is advantageous. >