The Differential Range Spectrum of Cosmic-Ray Mesons at Sea Level

The low energy region of the differential range spectrum of cosmic-ray mesons at sea level has been investigated by means of a counter controlled cloud chamber. The results obtained in the region from 18 g/${\mathrm{cm}}^2$ to 76 g/${\mathrm{cm}}^2$ of air equivalent absorber have proved to be about 20 percent higher than predictions based upon similar measurements at greater absorber thicknesses. A possible explanation of this discrepancy lies in the consideration of the effect of multiple scattering of mesons in previous experiments. The present experiment employs a geometrical arrangement of the apparatus which minimizes the corrections to be applied to the data to allow for loss of mesons from the apparatus due to scattering. The earlier work in the field has not been corrected for scattering effects and can, as a result, be expected to give too low a value of the spectrum. The average differential intensity of mesons measured in the range interval mentioned above is 6.86×${10}^{-6\mathrm{}}$ (particles/sec/sterad/g). The differential range spectrum of protons was also measured and is in good agreement with other work which measured the spectral values at somewhat higher energies than those encountered here. The proton intensity is 2.12×${10}^{-6\mathrm{}}$ (particles/sec/sterad/g) in the region 16.5 to 42.3 g/${\mathrm{cm}}^2$ of air equivalent and 0.67×${10}^{-6\mathrm{}}$ (particles/sec/sterad/g) in the region 42.5 to 63.3 g/${\mathrm{cm}}^2$ of air equivalent.