Penetrating Particles in Extensive Air Showers

Penetrating particles in extensive air showers have been studied at 4300- and 3260-m elevations. The particles capable of penetrating 14 cm lead are about 1 per 30 shower particles at 3260 m and 1 per 25 at 4300 m. The number of penetrating particles is reduced by a factor 1.8 when the lead is increased from 15.5 to 39 cm, and the density of the penetrating particles diminishes by a factor 1.7 between 4300 and 3260 m elevation. These facts imply the penetrating particles are very numerous and have too low average energy to be mesons coming from the top of the atmosphere. Further experiments show that they are not produced multiply in lead shields above the counters. This fact, together with the independence of their number on the atomic number of the absorber, seems to indicate they are not produced by photons.