Cosmic-Ray Ionization at High Altitudes

A criterion for the nature of cosmic rays. Cosmic rays may be interpreted as photons only if at all altitudes $\frac{d^2\left(log\psi \right)}{d{P}^2>0\mathrm{}}$, where $P$ is the barometric pressure and $\psi$ is the intensity as a function of the pressure for rays descending vertically through the atmosphere. Gross has shown how $\psi$ can be determined directly from the observed intensity $I$, due to rays from all directions. The rays may be interpreted as ionizing particles with a definite range ("$r$-particles") only if the relation $\frac{d^{2}I}{d{P}^2}>0\mathrm{}$ is satisfied. Measurements by a recording cosmic-ray meter, with walls equivalent to 6 cm of lead to avoid transition effects, were made on the recent Settle-Fordney stratosphere balloon flight. Through the altitude range from 40 to 15 cm Hg the ionization-pressure relation satisfies the criterion for $r$-particles but not that for photons. This result is confirmed by comparison with other high altitude data.