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 at 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 findings into account.