The cloud chamber photographs of Blackett and Occhialini, Anderson, and Lecher 1 have brought to light the suggestion that Hoffmann St&se may not originate in a single atom, but may arise from several atoms as the result of a primary cosmic ray acting through intermediaries.
Each of these observers finds groups of ray tracks, apparently all formed simultaneously.
These tracks are possibly produced by the particles which give rise to the bursts of ions observed in a pressure chamber.
However, these tracks do not diverge from a common point, but seem, in many cases, to be formed in several groups, each group of tracks diverging from a separate point. The existence of these multiple centers has been attributed by Lecher l to the action of neutrons which, coming from any one nuclear disintegration, serve to precipitate others. Experiments by IV. F. G. Swann and the author are in progress at the present time for the purpose of testing this conclusion further and particularly to ascertain whether the size of a Stoss depends upon the amount of material involved.
Data showing the frequency of occurrence of St&se of different sizes have been published by Steinke and Schindler, and by Messerschmidt 2 and similar data have been taken at the Bartol Foundation with an apparatus which has been previously described.3 These data all show the surprising fact that although a greater portion of the St&se is grouped around a definite size, St&se ten times this size occur fairly often. The object of the present note is to show how the cooperation of several atoms in the production of a Stoss would give rise to such a frequency distribution of Stoss sizes as is observed.