Mean mass of the abundant cosmic-ray nuclei from boron to silicon at 1. 2 GeV per atomic mass unit

Journal Article · Fri Sep 01 04:00:00 EDT 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156417· OSTI ID:6652262

Dwyer, R

We present the results of a comprehensive study of cosmic-ray isotopic composition above 1 GeV per amu. The mean mass of the elements B, C, N, Ne, Mg, and Si over the energy range 1.0--1.6GeV per amu and the implications for the cosmic-ray sources are given. The technique used employs the effect of the geomagnetic field on the cosmic-ray fluxes. The principle of the method is discussed, and details on the data analysis procedures are given. The instrument is a scintillation--liquid Cerenkov counter telescope with a multiwire proportional chamber hodoscope. It has been flown twice on high-altitude ballons from Palestine, Texas (vertical cutoff rigidity=4.5GV), yielding an exposure factor of 20 m/sup 2/ sr h. The measured mean neutron excess, -2Z, of the source elements C, Ne, Mg, and Si is 0.05 +- 0.03, 0.45 +- 0.10, 0.32 +- 0.11, and 0.26 +- 0.16, respectively, at the top of the atmosphere, normalized to a value for O of 0.06. The mean neutron excess for Ne, Mg, and Si at the source implied by these results is calculated taking into account the effects of galactic propagation. Although the errors are large, it is found to agree for all these elements with solar system isotopic composition. The mean neutron excess for nitrogen (the /sup 15/N fraction) is 0.45 +- 0.07 at the top of the atmosphere consistent with an origin for nitrogen principally by spallation in the interstellar medium. The amount of nitrogen required in the cosmic-ray source relative to carbon is 0.07 +- 0.02.

• Research Organization: Enrico Fermi Institute and Department of Physics, University of Chicago
• OSTI ID: 6652262
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 224:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
CHERENKOV COUNTERS
COSMIC NUCLEI
COSMIC RADIATION
COSMIC RAY SOURCES
GEOMAGNETIC FIELD
IONIZING RADIATIONS
MAGNETIC FIELDS
MASS
MEASURING INSTRUMENTS
NUCLEI
NUCLEOSYNTHESIS
PHOSPHORS
PLASTIC SCINTILLATORS
RADIATION DETECTORS
RADIATIONS