A study of non-flammable gas mixture for resistive plate counter

The RPC (resistive plate counter) has good time and position resolution. These factors make it an attractive candidate for trigger system at collider experiment. The standard gas mixtures (Ar+iso-C/sub 4/H/sub 10/+Freon) used in RPC are very flammable when leaked into air. In view of safety issue,we have studied non-flammable gas of Ar+CO/sub 2/+iso-C/sub 4/H/sub 10/+Freon as a function of ratio Ar:CO/sub 2/ allowed in non-flammable gas mixtures for the RPC with ABS electrodes. The basic performance of the various mixtures have been measured; singles (untriggered) count rate, detection efficiency and charge spectra versus operating voltage. We have found a set of non-flammable mixtures of the kind of Ar+CO/sub 2/+Freon contained less than /spl sim/8.4% of iso-C/sub 4/H/sub 10/ for K/sub L//muon counter of KEK B-factory at KEK.