On the Knock-On Secondaries of Penetrating Particles

The knock-on secondaries of penetrating particles emerging from Pb plates (15 g ${\mathrm{cm}}^{-2\mathrm{}}$) have been investigated by cloud chamber and by counter telescope. The frequency of occurrence and the observed spatial distribution of the secondaries with respect to the primary penetrating particles have been found to be in agreement for the two different methods. Further data are presented on the back scattering of secondaries in Pb plates and on the emergence of secondaries from thin pieces of wood and counter walls. The possible effects on counter experiments are discussed briefly.