Charge composition of cosmic rays between 4 and 100 GV

SEVERAL groups have reported the energy dependence of the charge composition of cosmic-ray nuclei with Z⩾ 3 (refs 1–5). The results suggest that the ratio of the numbers of nuclei in groups L and M (defined in Table 1) decreases as the rigidity increases. At 100 GV the ratio is about 25% lower than the value below 10 GV. There is, however, no general agreement about the variation with rigidity of the ratio of VH nuclei to M nuclei; a variable ratio would be evidence for the existence of more than one basic acceleration mechanism, because both charge groups are thought to consist mainly of particles coming directly from the sources. The largest variation in the ratio of VH to M nuclei is reported by Ormes and Balasubrahmanyan1. We report here the measurement of the ratios of L nuclei to M nuclei and of VH nuclei to M nuclei using a magnetic spectrometer. Our results are based on two balloon flights, the first from Palestine, Texas, on August 23, 1969, and the second on November 13, 1970, from Parana, Argentina. The combined exposure factor for these flights was 273 cm2 sr s at an average altitude of 3 g cm−2.