The Intensity and Masses of Cosmic-Ray Particles

Measurements have been made of the relative numbers of mesons and protons in the sea level cosmic radiation. The measurements include those particles that have ranges in lead between 4.0 and 13.0 cm. The masses were determined by observing the range and momentum of each particle. No evidence was found for any particles except positive protons ($\mathrm{mass}=1893\mathrm{}\pm 50m_e$) and positive and negative $\mu$-mesons ($\mathrm{mass}=196\mathrm{}\pm 3m_e$). The low value of the $\mu$-meson mass reported here may be due in part to the uncertainty of the range-energy relations in copper. As many protons as $\mu$-mesons were observed in the range interval from 4.0 to 13.0 cm of lead. The intensity of protons decreased with increasing range.