Über die schweren Kerne in der primären kosmischen Strahlung

Abstract

The present paper describes the results of an investigation on heavy nuclei (Z > 2) of the primary cosmic radiation. The measurements were made in 40 stripped emulsions flown over Sardinia (λ~40°) in a height of about 27 km for 7 hours. The energy of the nuclei was deduced from their multiple Coulomb scattering, and, if they fragmentated, from the opening angles of their secondary products. For the determination of the charge number Ζ the measurement of the δ-ray density was sufficient, all particles having energies/nucleon ≥ 1,3 GeV. The result is thus independent of possible influences of spurious scattering. The charge spectrum under an average of 32 g/cm2 of residual material shows that the number of nuclei with 3 ≤ Z ≤ 5 is approximately equal to that of nuclei with 6 ≤ Z ≤ 9. This is in agreement with the charge spectrum found by Dainton, Fowler, and Kent, but at variance with the results of Bradt and Peters. The magnitude of the correction to be applied for the scanning loss of Li-nuclei is discussed. The correction factor used by Dainton et al. appears to be too high. With regard to the influence of the residual material it is shown that the calculated intensity of the Li-, Be-, and B-nuclei at the top of the atmosphere will be strongly affected by the uncertainty of the probabilities pk i for fragmentation. The fragmentation probabilities found in this work are in good agreement with those obtained by Bradt and Peters and by Gottstein, they are, however, somewhat smaller than those measured by Noon, Kaplon, and Ritson. The values of the mean free paths in emulsion can be represented by a formula for the cross-sections given by Peters et al. The energy spectrum agrees with that deduced by Kaplon et al. from measurements of the latitude-effect. It was found that because of spurious scattering cell lengths of at least 4 mm are required in order to measure energies > 4 GeV/nucleon. A spectrum similar to that found by Dainton et al. is obtained, if one confines the scattering measurements on cells which are not long enough. The flux of nuclei Z ≥ 6 at the top of the atmosphere is somewhat smaller than measured by other authors at λ = 41°.