THE ELECTRONIC AVALANCHE IN PROPORTIONAL-COUNTERS

TEPCs are proportional counters with a central electrical field, which are operated with low pressure tissue-equivalent gases. The electron avalanche growth in such counters is quite unknown because they work a t high values of electrical field gradients and of reduced electrical field at the anode surface. An experimental methodology to investigate the electronic avalanche inside a TEPC has been set up at the Legnaro laboratories; a Monte Carlo code which describes microscopically the electron-molecule interaction has been set up by the Atomic Centre of Toulouse university. Experimental data and calculations are compared. The agreement is fairly good: it is a confirmation of the role of non- equilibrium effects in the electronic avalanche growth. The design of new TEPCs able to simulate nanometric dimensions has to take these fin dings into account.