Investigation of operation of a parallel,plate avalanche chamber with a CsI photocathode under high gain conditions

We report results of a systematic study of the operational characteristics of a single-step parallel-plate avalanche chamber with CsI photocathode under high-gain conditions at room temperature and 1 atm pressure. Different mixtures of He and Ar with hydrocarbons were tested, as well as with ethylferrocene vapor which are known to form an adsorbed photosensitive layer on the Csl photocathode. The chamber can reach high gains, up to 106, has a very good time resolution (500 ps FWHM), and an energy resolution of 8.2% FWHM for 3 ! 103 primary photoelectrons with a quantum efficiency of the CsI photocathode of about 20% at 193 nm. Photon feedback, caused by avalanche emission with wavelength longer than 200 nm, was observed for large total charge and found to be nearly independent of the concentration of quencher in the range 7 to 70 Torr. Breakdown appears at a total charge of 101° electrons and is always of the slow type. There is good proportionality up to the breakdown limit.