The inelastic cross section of $p$-air collisions [${\sigma }_{\mathrm{in}}(p-\mathrm{air})$] between ${10}^{16}$ and ${10}^{18}$ eV is estimated by the observation of extensive air showers at Akeno. The flux of air showers at different zenith angles is analyzed with both a fixed muon number and a fixed electron number. ${\sigma }_{\mathrm{in}}(p-\mathrm{air})$ increases with energy as $290\times E_{\mathrm{lab}}^{0.06\pm 0.01}$ mb ($E_{\mathrm{lab}}$ in teraelectron-volts) up to ${10}^{18}$ eV with the assumptions of Feynman scaling in the fragmentation region and at least 10% of the primary particles being protons.

• Received 15 March 1983

DOI:https://doi.org/10.1103/PhysRevLett.50.2058