p-air cross-section measurement at 1018.5 eV

We present the first measurement of p-air inelastic cross-section at 1018.5 eV using the HiRes stereo fluorescence detector data. A new measurement technique employing de-convolution of the Xmax distribution is proposed. Monte Carlo simulations with the CORSIKA air shower generator and QGSJet and SIBYLL2.1 interaction models are discussed.