The light received at Los Leones is nearly pure and after a small correction for scattered Cherenkov light and atmospheric absorption the number of charged particles can be determined using the fluorescence efficiency determined in laboratory experiments. Integration of this curve using a dE/dx of 2.2 MeV/gm/cm2
gives an electromagnetic energy of 4.9 x 1019
eV. Correcting for the energy carried by muons and neutrinos the total energy is estimated to be 5.4 x 1019
eV. The number of charged particles as a function of atmospheric depth is shown in Figure 3.