Showers in Lead Produced by Electrons with Energies from 300 MeV to 1 BeV

The behavior of electron-initiated showers in a lead-plate expansion cloud chamber has been measured for primary energies of 277, 528, 845, and 990 MeV, in terms of the secondary electrons with angles within about 60 deg of the shower axis. Empirical formulas are derived from the experimental data, for characteristic average shower quantities as functions of primary energy. The track length, for example, follows a relation of the form $L_T=0.073\mathrm{}{E_0}^{0.92}$ radiation lengths, where $E_0$ is measured in MeV. Expected standard errors in determining energies of individual showers by measuring the various quantities are also given. A new tabulation of the results of Wilson's Monte Carlo calculations is given for primary electrons and photons with energies from 50 to 300 MeV. The average numbers of electrons with energies greater than 8 and 10 MeV given in this paper correct the originally published curves and are in good agreement with the results of Crawford and Messel. Approximate comparison is made between the experimentally measured shower behavior and the calculated behavior, and good agreement is found.