ON THE 2-STAGE OPERATION MECHANISM OF LOW-PRESSURE MICROSTRIP GAS-CHAMBERS

A two-stage multiplication mechanism has been observed in microstrip g as chambers (MSGC) operated in a pressure range of 10-50 Torr of isobu tane. The resulting high gain (> 10(4)) of single electrons photo-prod uced on a CsI photocathode is attributed to a preamplification in the gas gap followed by anode strip multiplication. The large and fast ris e of the induced pulse in this mode leads to an efficient single elect ron detection at relatively low charge gain. The reduced positive ion feedback preserves radiation convertors coupled to such electron multi pliers from sputtering damage. MSGCs operated in this mode are expecte d to have a subnanosecond time resolution and very high rate capabilit y. Some potential applications are briefly discussed.