BEHAVIOR OF THE SQS MODE OBSERVED AS A FUNCTION OF THE RADIAL DISTANCE OF THE POSITION OF PRIMARY IONIZATION

In the transition region from proportional to the self-quenching strea mer (SQS) mode in Ar + 30% CH4 gas mixture, the degree of gas amplific ation and the transition probability to the SQS mode have been studied as a function of r, where r is defined as the radial distance between the position of primary ionization and the anode wire. It is found fo r the first time that an enhancement of the SQS transition occurs for small r in the vicinity of the anode wire, however, the degree of gas amplification for the SQS mode is independent of r. The results may in dicate that the structural change of primary-electron cloud caused by the diffusion effect influences the transition probability from propor tional to SQS mode.