Proton Intensities at Sea Level and 9000 Feet

The vertical intensities of protons which occur singly in the cosmic radiation have been measured at 9000 feet and at sea level. The particles observed were those whose momenta, recorded by cloud chambers above and below a magnetic field, were between 0.59 and 0.93 Bev/c after having traversed various thicknesses from 0 to 345 g/${\mathrm{cm}}^2$ of lead absorber placed over the apparatus. The identification of the particles was achieved by a mass determination based on the measured momentum and the range observed in a third cloud chamber containing copper plates. With no absorber over the apparatus, the differential momentum intensity at 9000 feet was found to be 8.9±0.9×${10}^{-4\mathrm{}}$ ${(\mathrm{B}\mathrm{e}\mathrm{v}/\mathit{c})}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sterad}}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$. In conjunction with the data obtained at sea level with the same apparatus, an effective absorption length of ${136}_{-8\mathrm{}}^{+13\mathrm{}}$ g/${\mathrm{cm}}^2$ of air was found for protons of the mean momentum 0.76 Bev/c. From this absorption length and the evidence that production between the two levels of observation plays a predominant role, a value of 134 g/${\mathrm{cm}}^2$ for the absorption length of the primary particles was deduced.