LARGE-SCALEMULTILAYERPROPORTIONALCOUNTERSYSTEM USED IN THE EXTERNALPARTICLEIDENTIFIER(EPI)AT CERN

A matrixof 4096gas proportional countersof 6 x 6 cm2 cross section and 1 m heightarrangedin 128 layers of 32 cellseachis usedfor identificationof fastpions,kaonsand protonsemergingfromhadroninteractionsin the3.7m bubblechamber (BEBC).Particleseparationin the momentumrangeup to at least70 GeV/c is achievedby ionizationsamplingin theregionof therelativistic rise. ResolutionindE/dxof 6% FWHM (2.5%RMS)was reachedandmaintained over extendedrunningperiods.The relativistic risewas measuredin the momentumrangeof 20-110GeV/c.The resultsof theEPI tests are usedin analysisof certainpracticalaDplicationlimitsof thedE/dxsampling method.