Ion-pair clusters and excited-state yields in radiolysis

It is stated that when β or γ rays are absorbed in matter sparse tracks of ion pairs are produced and the secondary electrons formed sometimes have enough energy to produce further ion pairs as small clusters. Distributions of cluster size in a cloud chamber were measured by Wilson (1923), and results showed that nearly two thirds of the ion pairs occurred in clusters. Similar behaviour should occur in other phases, but little is yet known of the role of clusters in radiolysis. The behaviour of hydrocarbons is discussed. If ion pair recombination products are considered, and especially the yields of singlet and triplet excited states, cluster formation must be taken into account. (U.K.)