Isotopic composition and energy spectrum of low-nergy helium nuclei in primary cosmic radiation

Abstract

The isotopic composition and the energy spectrum of low‐energy helium nuclei have been investigated, using a nuclear emulsion stack flown from Fort Churchill, Canada, on August 4, 1962. The proportion of He3 nuclei at the top of the atmosphere was determined to be 18±5% within the kinetic energy interval of 160–370 Mev/nucleon and 24±8% within the rigidity interval 1.1–1.4 bv/c. The differential energy spectrum in the above energy interval was found to have a maximum around 275–300 Mev/nucleon. Assuming that there is no He3 at the cosmic‐ray sources, and that the observed abundance reflects the interactions of the primary radiation in its passage through interstellar matter, we conclude that the low‐energy primary radiation has traveled a total of 6±2 g/cm2 in this medium. This result is found to be consistent with the values obtained from the low‐energy lithium, beryllium, and boron experiment. The implications of these results are examined on the basis of different models used for the propagation of cosmic radiation through interstellar matter.

The Charge Spectrum and Interactions of Relativistic Heavy Nuclei in the Primary Cosmic Radiation

“…In more recent work, the "range" criterion, i.e. counting 6 rays that extend beyond a given distance from the track, has been used by Daniel and Durga Prasad (1962) and by others as well, and, in general, more reliable results have been obtained, particularly for nuclei of higher charges. Furthermore, the results are not affected very much by any unevenness in development of the en~ulsions.…”

“…The amount of matter traversed by the primary cosmic rays can therefore be estimated on the assumption that all of the Li, Be, B, and 3He nuclei arriving a t the top of the atmosphere are due t o fragmentations of heavier nuclei during their passage through interstellar space. Further experiments have been carried out by Aizu et al (1960), Icoshiba et al (1963), Evans (1963, Foster and Debenedetti (1963), Badhwar et al (1965a), and also by others to determine the energy dependence of the relative abundances of the light nuclei, and by Aizu (1963), Dahanayake et al (1964), and Hildebrand et al (1963) on years the precision of charge determination in nuclear emulsions has beell improved greatly, especially for relativistic nuclei. Consequently, questioils such as the relative intensities of the C, N, 0, and F nuclei, the ratio of the numbers of nuclei with even charges to those with odd charges in the I-I3 group (10 ,< Z ,< 15), and the presence of the I-12 group of nuclei (16 ,< Z ,< 19) in the primary radiation can now be discussed with more meaning.…”

“…T o correct our results for the ascent and descent of the balloon, and for extrapolation t o the top of the atmosphere, the interaction inean free paths in air calcuIated by Daniel and Durga Prasad (1962) have been used. T h a t these values are approxiinately correct is indicated by the relatively good agreement between the calculated and measured mean free paths in emulsion, although the present results indicate t h a t the theoretical values inay be rather high.…”

“…In recent years it has been definitely established that the flux of Li, Be, and B nuclei in the cosmic radiation is not negligible a t the top of the atmospllere (Waddington 1 9 6 0~) ; O'Dell et al 1962;Daniel and Durga Prasad 1962;and others). A similar result \vas obtained for 3He nuclei by Appa Rao (1961), Aizu (1962), and Hildebrand et al (1962).…”

The propagation of cosmic-ray nuclei in interstellar space and solar system

“…Various other models, especially the three-dimensional model has been considered by others (Ginzburg and Syrovatsky, 1961, Mathiesen and Stenman, 1965, Dahanayake et al, 1964 to explain the dependence of the ratio of L-nuclei as a function of energy. Kaplon and Skadron (1964) found an increase in the path length with decreasing energy, which they explained as due to the preferential confinement of low energy particles by the magnetic fields in the source regions.…”