The Absorption Mean Free Path of Large Hard Showers in Air

In this report an experiment is described in which altitude curves of hard showers of various sizes produced in a lead block were obtained. The sizes were determined by means of a hodoscope; for the largest hard shower group a minimum energy of 260 Bev was estimated by extrapolation to the top of the atmosphere. All altitude curves show an exponential absorption in the atmosphere with a mean free path of \ensuremath{\sim}125 g ${\mathrm{cm}}^{\ensuremath{-}2}$. It appears that these large attenuation lengths are difficult to reconcile with a geometric collision mean free path for a nucleon-nucleus collision.