The Emission of Slow Positive and Negative Mesons from Nuclear Disruptions Produced by Cosmic Radiation

Microscopic examination of 76 cc of thick (300 to 1800 microns) nuclear emulsion exposed in the stratosphere has revealed 168 events in which slow mesons are created and terminate their range in the recording medium. Basing the identification of sign on either $\pi -\mu$ decay or $\sigma -\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{r}$ formation at the range terminus, 26 of the ejected particles were ${\pi }^{+}$ mesons and $145{\pi }^{-}$. The small value of the $\frac{{\pi }^{+}}{{\pi }^{-}}$ ratio is attributed chiefly to the production of the ejected mesons by neutral radiation. The observational frequency of the ejected ${\pi }^{-}$ mesons increases rapidly with star size and is approximately proportional to the square of the excitation energy of the parent star. In two events initiated by charged primaries several slow negative mesons were ejected as the wide angle members of large showers of particles. In general, the energy of the slow mesons is between 0.3 and 40 Mev. Corrected for escape from the emulsion the average frequency of the ${\pi }^{-}$ meson production is proportional to $E^{0.6}$ for $E\le 8$ Mev and to $E^{2.3}$ for energies between 8 and 40 Mev. Comparison of the data on ejected mesons with that available on cyclotron mesons indicates close similarity in the form of the secondary star spectra, the $\frac{{\pi }^{+}}{{\pi }^{-}}$ ratio and the energy distribution of slow ${\pi }^{-}$ mesons.