Chemical Composition of Relativistic Cosmic Rays Detected above the Atmosphere
Abstract
Final results on the first satellite experiment on abundances of cosmic-ray nuclei having a mean energy of several GeV per nucleon are presented. A nuclear-emulsion detector, exposed on Gemini XI in a near-equatorial orbit ranging between geographic latitudes +/-29°, collected 619 high-quality tracks above the earth's atmosphere. Time resolution (within about 5 min) was provided by movement of a lower emulsion stack relative to an upper one. The detector was covered by only 0.07 g/cm2 of aluminum and was favorably oriented for 18 h. The results on abundances, requiring no correction for secondary production in the atmosphere, are characterized by (a) a pronounced odd-even effect, with low abundances for elements of atomic number 7, 9, 11, and 13, compared to those of neighboring elements with even Z; (b) approximately equal fluxes of neon, magnesium, and silicon, each being about one-fourth that of oxygen; and (c) an abundance gap in the region 15<=Z<=19. The observed ratios of Be+B, 10<=Z<=19, and Z>=20 to the medium group, 6<=Z<=9, provide no evidence for significant variation of composition with rigidity between 3.5 and 30 GV. A primordial composition-prior to interactions of the cosmic rays with the interstellar medium-is calculated. This source composition is compared with "universal" and solar abundances.
- Publication:
-
Physical Review D
- Pub Date:
- February 1970
- DOI:
- 10.1103/PhysRevD.1.1021
- Bibcode:
- 1970PhRvD...1.1021D