Determination of the Neutron-Proton Ratio in Primary Cosmic Rays

Abstract
The charge ratios of muons produced by the interaction of 400-GeV protons with thick copper targets were measured and the +/- ratios were found to be much larger than similar ratios for muons in the secondary cosmic rays. The difference between these charge ratios is taken to indicate that the neutron/proton ratio in the primary cosmic rays is quite large: i.e., of the order of 25:75.