High energy nuclear interactions of cosmic ray particles close to the top of the atmosphere

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A study of the altitude and latitude dependence of the various cosmic ray components provides information on the nature of high energy nuclear interactions of cosmic ray particles close to the top of the atmosphere. Counter telescopes have been flown with plastic balloons to a maximum altitude of 94000 ft. Intensity vs. pressure curves have been obtained at geomagnetic latitudes of λ=55°, 41° and 28° for the total cosmic radiation and for the components capable of traversing 4, 7.5 and 12 cm of lead. The energy spectrum of primary cosmic ray particles has been derived from the extrapolation of the intensity of the total radiation to the top of the atmosphere. The integral momentum spectrum of the total primary radiation is given byN(>pc/Ze)=0.48(pc/Ze)−1.0. Subtracting the known contribution of primary α-particles and heavier nuclei the spectrum of primary protons becomesP(>pc/e)=0.43(pc/e)−1.0. Results indicate that the radiation originating from primaries in the energy range of 1 to 4 GeV (cutoff energies at λ=55° and 41°) is predominantly of a nucleonic nature. The absence of an electronic component can be explained by assuming that, close to the top of the atmosphere, electrons originate predominatly from the decay of neutral mesons and that in this energy range the probability of producing mesons is quite small. In sharp contrast, the soft component originating from primaries in the range of 4 to 8 GeV (cutoff at λ=41° and 28°) multiplies rapidly in the atmosphere. This large transition effect in air with a maximum at about 10 cm Hg pressure is characteristic of electron showers. It is concluded that the probability of producing neutral mesons singly reaches nearly its saturation value at energies of the primary radiation between 4 and 8 GeV. At energies higher than 8 GeV this effect is even more pronounced due to the contribution of the plural production of mesons. In order to study the production of mesons in the interaction of cosmic ray particles with a liquid Hydrogen target, a counter experiment was carried out at an altitude of 90,000 ft. During the first half of the experiment, an average of 1.6 g/cm2 of Hydrogen was interposed between the counters. The Hydrogen was then ejected and data obtained during the remaining portion of the flight at altitude. From the narrow angular distribution of the events originating in liquid Hydrogen (total angular spread ∼15°), sharply different from those originating in the walls of the Dewar container (minimum angular spread ∼50°), it is concluded that they were produced by very high energy primary particles. It is estimated that the events in Hydrogen resulted mostly (80%) from the interaction of primary protons of an average energy of 50–100 GeV in which a minimum of four mesons were produced. Penetrating showers in lead have been investigated at λ=55° and 28°. Between these two latitudes, at an atmospheric pressure of 1.5 cm Hg, the ratio of the radiation producing penetrating showers amounts to 1.5, as compared to 2.9 for the hard component and 4.1 for the total radiation.