On the Production of the Hard Component of the Cosmic Radiation. I. The Photon Hypothesis

Abstract

The number of quanta (and electrons) of energy $k$ within $\mathrm{dk}$ times their range in units of radiation theory (photon lengths) produced in matter by a primary electron of energy $E$ is calculated from the theory of showers to be $Z\left(k\right)dk=\alpha \left(\frac{E}{k^2}\right)dk$, where $\alpha =0.57\mathrm{}$ for quanta and 0.44 for electrons. With the help of the known energy distribution of the electrons coming from the outside, the energy distribution of photon lengths in the higher atmosphere is obtained. A comparison with the number and energy distribution of mesons (obtained from data near sea level and underground) leads to the following consequences of the hypothesis that the mesons are created by photons. The production process must be of moderate multiplicity and its cross section must increase from about 1/100 of the cross section for pair production by photons in air at moderate energy (7 to 10 Bev) to about 1/10 at higher energy (over 18 Bev). These high cross sections required for the production of energetic mesons seem to imply correspondingly large cross sections for absorption and constitute a serious difficulty for the understanding of their great penetrating power.