Measurement of the isotopic composition of cosmic-ray Fe and other nuclei with Z = 20 to 25

Journal Article · Sat Jan 01 04:00:00 EST 1977 · Astrophys. Lett.; (United States)

OSTI ID:6404318

Simpson, G A; Kish, J; Lezniak, J A; Webber, W R

Measurements of the isotopic composition of cosmic-ray Fe nuclei and other nuclei with Z > or = 20 are reported. These are the first measurements with a mass resolution sigma, significantly less than 1 AMU in this charge range, and as a result it is possible to determine the individual isotopic composition of Fe and the other heavier nuclei. The technique for mass separation utilizes a Cherenkov x total energy measurement. The energy range of analysis is restricted to a relatively narrow interval of approximately 130 MeV/nuc for Fe, thus permitting a mass resolution = 0.40 +- 0.06 AMU. A total of approximately 80 Fe nuclei are analyzed for their isotopic composition, approximately 67% of which are /sup 56/Fe; significant fractions of /sup 58/Fe and /sup 54/Fe are also observed. A careful correction for atmospheric and instrumental effects is made. The corrected abundances at the top of the atmosphere are compared with those predicted by a leakage lifetime propagation model with various trial source distributions. The source abundances of Fe isotopes are found to be /sup 56/Fe = 65 +- 10%, /sup 58/Fe = 28 +- 8% and /sup 54/Fe = 11 +- 9%. The clear presence of a significant amount of /sup 58/Fe in the source requires the nucleosynthesis of cosmic-ray Fe nuclei to occur in a region of greater neutron excess than the material found in the solar system. Nuclei with Z = 20 to 24 generally have an isotopic abundance consistent with a fragmentation origin. An exception to this may be Ca. This charge has an abundance larger (approximately 28% of Fe) than can apparently be accounted for by fragmentation; however, the dominant isotope is /sup 42+-1/Ca rather than the expected /sup 40/Ca. A total cross section for Fe fragmentation to Ca approximately 70 mb, or about 1.5 x the empirically calculated cross section at approximately 700 MeV/nuc, is required to explain the data if Ca is assumed to be entirely secondary.

• Research Organization: Univ. of New Hampshire, Durham
• OSTI ID: 6404318
• Journal Information: Astrophys. Lett.; (United States), Journal Name: Astrophys. Lett.; (United States) Vol. 19:1; ISSN ASTLA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CHEMICAL COMPOSITION
CORRECTIONS
COSMIC NUCLEI
COSMIC RADIATION
COSMIC RAY DETECTION
DETECTION
ELEMENTS
ENERGY SPECTRA
IONIZING RADIATIONS
IRON
MASS SPECTROSCOPY
METALS
NUCLEI
NUCLEOSYNTHESIS
RADIATION DETECTION
RADIATIONS
SPECTRA
SPECTROSCOPY
TRANSITION ELEMENTS