Absorption Curve of Cosmic Rays Obtained in the Stratosphere

In the paper under review[^1], measurements were made of the absorption of cosmic rays in lead by means of a telescope made of counters, raised on balloons to an altitude of 20 km (pressure 5.7 cm Hg). At this altitude, where the intensity of the soft component is close to its maximum, the balloons remained for 6.5 hours. The readings of the telescope (flashes of neon lamps) were recorded on motion-picture film. The apparatus was recovered 700 km from the launch site. The telescope scheme is shown in Fig. 1. The radio-engineering circuit recorded coincidences in the telescopes $ABCF$, $BCDH$, $CDFJ$, $DFJK$, $FJKL$, and $GHLM$.

Fig. 1.

Fig. 2.

Geometrically these telescopes are identical, and such coincidences give, as is evident from Fig. 1, the number of particles that passed through, respectively, 0, 2, 4, 8, 12, and 18 cm of lead. The absorption curve obtained in this way is shown in Fig. 2, where the absorption curve at sea level[^2] is also given. A comparison of the two curves clearly shows the difference between the composition of the radiation at these two altitudes. The rapid absorption in the first centimeters of lead is characteristic of the electron component. The hard component in the stratosphere is absorbed considerably more rapidly than at sea level, where the entire hard component consists of $\mu$-mesons. From Fig. 2 it follows that the absorption coefficient of the hard component in the stratosphere is equal to 220 g/cm², which corresponds to the absorption coefficient

protons and neutrons of high energy, of which the principal part of the hard component at an altitude of 20 km consists.

Additional evidence for the absence of an appreciable number of $\mu$-mesons at this altitude is provided by the measurement of the absorption of cosmic rays in air, carried out with the same apparatus between altitudes of 23 and 15 km (pressures 4 cm Hg and 12 cm Hg).

These measurements showed anomalously large absorption in air, which would be expected because of the decay of $\mu$-mesons. It follows from this that $\mu$-mesons constitute a small part of the radiation at these altitudes.

A. V.

References

1. M. Schein and V. Jngve, Phys. Rev. 85, 4, 607 (1952).
2. W. Nielsen and K. Morgen, Phys. Rev. 54, 245 (1938).