Narrow Air Showers of Cosmic Rays. III. Further Absorption Measurements

Abstract

LETTERS TOMaryland) are used. We find that 14.7 percent of the bursts at low barometer and 17.4 percent at high barometer are due to /i-mesons and must be subtracted. The resulting ratio is 1.227d=5.2 percent, which becomes 1.207dt5.2 percent when similarly corrected for bursts produced by non-vertical radiation. This corresponds to a mean absorption path in air of 61 ± 17 g/cm 2 and to a barometric coefficient 4 of -2.2 (±0.6) percent per mm Hg. It is noteworthy to point out that the mean free path of 61 g/cm 2 corresponds to a cross section for nuclear collisions, which is very nearly equal to the cross-sectional area of an air nucleus.The energy necessary to produce the electronic cascades of which these bursts consist is of the order of 10 8 ev per particle. 2 Hence, we are dealing with energies of 2X10 10 ev and greater. This large absorption in air indicates that for these energies elastic scattering is practically zero. The bursts at Climax, then (except those produced by /z-mesons), probably originate from primary protons and perhaps to some extent from first generation 7r-mesons. If one assumes that the bursts come from the decay of neutral mesons which comprise f of all mesons produced, one finds that 6X10 10 ev must go into meson production in the collision which produces a burst of 200 particles. This represents a lower limit to the energy of our bursts producing radiation.Assuming an angular distribution corresponding to an exponential absorption of 9 or 10 mean paths, 5 a vertical flux of 0.5X10"" 6 particles cm -2 sec." 1 steradian" 1 is obtained at an atmospheric depth of 675 g/cm 2 (Climax) for energies £>6X10 10 ev. This corresponds to a vertical flux at the top of the atmosphere of the order of magnitude of 0.004 to 0.01 particles cm -2 sec. -1 steradian -1 , and this is not in disagreement with Winckler's estimate 6 of 0.004 particles cm -2 sec." 1 steradian" 1 for energies greater 7 than 6X10 10 ev.The author is indebted to his sponsor, Professor Marcel Schein, for many valuable discussions and suggestions. The Carnegie ionization chamber was provided through the courtesy of the Carnegie Institution of Washington. Thanks are also due to the Climax Molybdenum Company for its hospitality and cooperation. * Assisted by the joint program of the ONR and AEC. 1