The Charge Spectrum of the Cosmic Radiation at 41° N

From a large stack of G-5 emulsions flown at Texas, 41° N geomagnetic latitude, the charge spectrum of the cosmic radiation at 104 000 feet was obtained. Special emphasis is given to the observation of the detailed shape of the spectrum in the regionZ > 9. The gap-counting is extensively used even at these highZ values after very careful calibration with break-up events and δ-ray countings. The charge spectrum thus obtained was extrapolated to the top of the atmosphere by making use of the fragmentation probabilities in air which were obtained from the analysis of a total of 209 interactions in the same stack. This extrapolation gives for the ratio of the light nuclei, L, (Z = 3, 4 and 5) and the heavy nuclei, H, (Z ⩾ 9), to the medium ones, M, (Z = 6, 7 and 8) the values 0.32 ± 0.07 and 0.48 ± 0.10, respectively, at the top of the atmosphere. The fragmentation probabilities in hydrogen, the main constituent of interstellar matter, were also obtained from the careful study of the interactions in the stack and allowed to make a further extrapolation of the charge spectrum from the top of the atmosphere to the one at the source region of the cosmic radiation. The ratio of the heavy nuclei to the medium ones was found to be 0.66 ± 1.6 at the source. This charge spectrum at the source region is compared with the average chemical abundances of the elements in the universe as well as with those in certain types of stars. The results seem to indicate a close similarity of the chemical abundance curve of the cosmic radiation with that of certain types of young stars.