Performance of a gas avalanche pixel detector of 50 /spl mu/m pitch

We describe the performance of a square microdot (MDOT) detector of 50 /spl mu/m pitch, in terms of defocusing effect and gas gain. Both the count rate variation measurement and the computer simulation showed that the defocusing effect disappeared in the 50 /spl mu/m pitch MDOT. Initial charge buildup on the detector surface was also minimized when the small lateral dimension was combined with surface coating. The maximum gas gain was limited to /spl sim/1200 due to the small distance available for avalanche multiplication. We also developed a two-level microdot, namely closed-end gas electron multiplication (CEGEM) chamber. A CEGEM detector having a pitch of 200 /spl mu/m, holes of 40 /spl mu/m width and a spacer layer of 18.5 /spl mu/m thickness showed a maximum gain of /spl sim/400. This gain is expected to increase by increasing the spacer layer thickness and adjusting the hole size.