A UV-LIGHT PHOTO-DETECTOR BASED ON A MICROGAP CHAMBER WITH SINGLE-ELECTRON RESPONSE

A MicroGap Chamber (MGC) used as a fast UV light detector with single electron sensitivity is presented, The detector has a semitransparent or reflective CsI photocathode, 100-200 mu m anode pitch and 2D capabi lity. It works with gas mixtures based on DME and light noble gases at atmospheric pressure. A gas gain >10(6) has been achieved with a two- stage gas amplification (G > 10(2) in the drift region and G approxima te to 10(4) in the strip region). The use of light noble gases, like n eon, has brought to a sensible reduction of VUV light output (hence ph oton feedback) during electron multiplication in gas. Due to the very thin gap (5 mu m) a very large fraction of the avalanche charge is qui ckly delivered to the fast amplifier (20 ns peaking time) thus improvi ng the single electron detection capability of the MGC. Because of its higher gain the MGC with a semitransparent CsI photocathode provides a better single electron detection efficiency (>90%) than the MGC with a reflective photocathode. This latter, vice versa, has a higher quan tum efficiency and a faster response. Experimental results on gas gain , drift properties, positional sensitivity and single electron detecti on efficiency are reported.