Muons (>or=1 GeV) in large extensive air showers of energies between 1016.5eV and 1019.5eV observed at Akeno

The properties of muons (>or=1 GeV) in giant air showers between 10 16.5 eV and 10 19.5 eV are measured by the Akeno 1 km 2 , 20 km 2 and 100 km 2 air shower arrays. The lateral distribution of muons is well fitted by the formula given by Greisen (1960) with parameters beta =2.52+or-0.02 and log(R 0 )=(0.58+or-0.04) (sec theta -1)+(2.39+or-0.05) between 10 16.5 eV and 10 19.0 eV within 800 m of the air shower axis, where theta is the zenith angle of the shower arrival direction. The relation between the total number of muons (N mu ) and the total number of electrons (N e ) derived using these parameters is expressed on average as N mu =(2:6+or-1.3)*10 5.0+ alpha (N e /10 7 ) b where alpha =(1.07+or-0.13) (sec theta -1) and b=(0.77+or-0.02)-(0.17+or-0.02) (sec theta -1). The lateral distribution of muons becomes steeper than expected from extrapolation of the above formula for core distances >800 m and is expressed as rho mu =N mu (C' mu /R 0 2 )r -0.75 (1+r) - beta (1+(R/800 m) 3 ) - delta (r=R/R 0 , where R is a core distance). No deviation from this formula has been observed for sec theta <2.0 up to 10 19.0 eV. The relation between the muon density (S(600)) and the charged-particle density on the ground at 600 m from the core (S(600)) is studied between 10 16.5 eV and 10 19.0 eV. A systematic change in the chemical composition of cosmic rays from a predominantly heavy to a predominantly light composition above 10 17.5 eV claimed by the Fly's Eye group has not been detected beyond the present experimental uncertainties. The present experiment suggests a much smaller rate of change of composition between 10 17.5 eV and 10 18.5 eV than that from the Fly's Eye experiment.