Penetrating Showers in Carbon

The penetrating showers generated in carbon by the cosmic radiation have been investigated by means of a cloud chamber containing both carbon and lead plates which was operated at an elevation of 12,000 ft. It is shown that the penetrating showers generated in carbon are closely the same in angular distribution and in average multiplicity of penetrating particles as the penetrating showers produced in lead, comparison values in lead being obtained from previous work with the same cloud chamber containing only lead plates. Penetrating showers produced in the carbon plates were followed not infrequently by production of secondary penetrating showers farther down in the carbon; the initiating particles of the subsequent showers are very closely aligned with the direction of the primary particles of the parent penetrating shower. The mean free path of the lightly ionizing secondary particles of the penetrating showers for subsequent production of nuclear events was found to be 237±29 g/${\mathrm{cm}}^2$ carbon. The mean free path of the penetrating particles for large-angle scattering in the carbon is about four times this value. The electronic cascades produced at the same time as the penetrating component are satisfactorily explained in order of magnitude by assuming that they are produced by high energy gamma-rays which originate at the event or which may be derived from the fast decay of neutral mesons very near the original event.