 The "first Townsend coefficient" ( α ), also known as "first Townsend avalanche coefficient" is a term used where secondary ionisation occurs because the primary ionisation electrons gain sufficient energy from the accelerating electric field, or from the original ionising particle.The coefficient gives the number of secondary electrons produced by primary electron per unit path length.Townsend, Holst and Oosterhuis also put forward an alternative hypothesis, considering the augmented emission of electrons by the cathode caused by impact of positive ions.