THE BORON-TO-CARBON ABUNDANCE RATIO AND GALACTIC PROPAGATION OF COSMIC RADIATION

Journal Article · Sun Jun 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/752/1/69· OSTI ID:22037070

Obermeier, A; Boyle, P; Mueller, D ^[1]; Hoerandel, J ^[2]

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1. Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)
2. Department of Astrophysics, Radboud Universiteit Nijmegen, 6525 HP Nijmegen (Netherlands)

In two long-duration balloon flights in 2003 and 2006, the TRACER cosmic-ray detector has measured the energy spectra and the absolute intensities of the cosmic-ray nuclei from boron (Z = 5) to iron (Z = 26) up to very high energies. In particular, the second flight has led to results on the energy spectrum of the secondary boron nuclei, and on the boron abundance relative to that of the heavier primary parent nuclei, commonly quantified as the 'B/C abundance ratio'. The energy dependence of this ratio, now available up to about 2 TeV amu{sup -1}, provides a measure for the energy dependence of cosmic-ray propagation through the Galaxy, and for the shape of the cosmic-ray source energy spectrum. We use a Leaky-Box approximation of cosmic-ray propagation to obtain constraints on the relevant parameters on the basis of the results of TRACER and of other measurements. This analysis suggests that the source energy spectrum is a relatively soft power law in energy E{sup -{alpha}}, with spectral exponent {alpha} = 2.37 {+-} 0.12, and that the propagation path length {Lambda}(E) is described by a power law in energy with exponent {delta} = 0.53 {+-} 0.06, but may assume a constant residual value {Lambda}{sub 0} at high energy. The value of {Lambda}{sub 0} is not well constrained but should be less than about 0.8 g cm{sup -2}. Finally, we compare the data with numerical solutions of a diffusive reacceleration model, which also indicates a soft source spectrum.

• OSTI ID: 22037070
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 752; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
APPROXIMATIONS
ASTROPHYSICS
CARBON
COMPARATIVE EVALUATIONS
COSMIC NUCLEI
COSMIC RAY PROPAGATION
COSMIC RAY SOURCES
ELEMENT ABUNDANCE
ENERGY DEPENDENCE
ENERGY SPECTRA
GALAXIES
IRON
NUMERICAL SOLUTION
TEV RANGE