Pion Production by Electrons

The production of ${\pi }^{+}$-mesons directly by 500-Mev electrons has been studied in lithium. The measurements consist of a precise measurement of the ratio of electron-produced to bremsstrahlung-produced pion yields. Results expressed as "equivalent radiation length" $X_e$ for electron production are $X_e=0.0233\mathrm{}\pm 0.0012$ for pions of 55 Mev, and 0.0185±0.0014 for pions of 150 Mev at 75° to the incident electron beam. The results are fully compatible with purely electromagnetic interaction of the electrons. Within the limitations of the experimental data obtained to date, and of the available theoretical studies, the results are compatible with magnetic-dipole absorption as the predominant process in photopion production under the conditions indicated.