Progress in CsI-wire chamber imaging photomultipliers and single electron counters

Electrons photoproduced by UV-photons on a CsI photocathode, or deposited by ionizing particles and ultrasoft x- rays in low-pressure gas media, are efficiently detected in low pressure multistep avalanche electron multipliers. A solid photocathode avalanche chamber (SPAC) imaging photomultiplier was coupled to a Xe-filled gas scintillation detector. Its performance when exposed to 60 KeV x rays is presented. The stability of the CsI photocathode is discussed in detail. The latest experimental results from primary ionization cluster counting of charged particles and ultrasoft x-rays are presented. UV laser-induced ionization and Monte-Carlo simulations are used to study the processes involved. (author)