On the Range Spectrum of µ-Mesons at Sea-Level at Geomagnetic Latitude 24°N

Differential intensities of µ-mesons at sea-level at 24°N have been measured for the residual range equivalent to from 44 to 430 g/cm 2 of the air using a delayed coincidence method. It was found that the obtained range spectrum was nearly flat for present ranges and was 20 percent lower than Rossi's curve which should be valid at geomagnetic latitude greater than 45°. The effect of the lateral displacement as well as the angular deflection of particles in the absorber was taken into account for the scattering correction. Mesons locally produced in the absorber was found to be at most a few per cent of all mesons that stop and decay in the apparatus. This fact suggests that the discrepancy between µ-meson spectra by the absorption method and by the magnetic cloud chamber method can not be accounted for only by the local π-meson production.