MONTE-CARLO SIMULATION OF XENON FILLED CYLINDRICAL PROPORTIONAL-COUNTERS

Single electron avalanche processes in a xenon filled cylindrical prop ortional counter have been simulated using a detailed Monte Carlo tech nique. The avalanche gain A and its average value M, as well as its fr equency distribution and spread parameter b have been calculated for x enon at atmospheric pressure, for a 2.55 cm cathode radius and 12.5 an d 50 mum anode radii. A discussion is made of the results obtained for M as a function of the anode voltage in terms of prevailing theories. It is found that Monte Carlo calculated M values are markedly lower t han those obtained analytically using the first Townsend ionization co efficient calculated under a uniform field. This puts into evidence th e relevance of the non-equilibrium nature of avalanche processes.