The isotopic composition of cosmic-ray beryllium and its implication for the cosmic ray's age

Details The isotopic composition of cosmic-ray beryllium and its implication for the cosmic ray's age The isotopic composition of cosmic-ray beryllium and its implication for the cosmic ray's age

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...423..426l&link_type=abstract

The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 423, no. 1, p. 426-431

Astronomy and Astrophysics

Astrophysics

56

Beryllium Isotopes, Chemical Composition, Cosmic Rays, Interstellar Matter, Mathematical Models, Wave Propagation, Abundance, Energy Dissipation, Particle Acceleration, Spallation

Scientific paper

We report a new measurement of the cosmic-ray isotopic composition of beryllium in the low-energy range from 35 to 113 MeV per nucleon. This measurement was made using the High Energy Telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1991. In this overall time period of 14 years the average solar modulation level was about 500 MV. The cosmic-ray beryllium isotopes were completely separated with an average mass resolution sigma of 0.185 amu. The isotope fractions of Be-7, Be-9, and Be-10 obtained are 52.4 +/- 2.9%, 43.3 +/- 3.7%, and 4.3 +/- 1.5%, respectively. The measured cosmic-ray abundances of Be-7 and Be-9 are found to be in agreement with calculations based on standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the recent cross sections of the New Mexico-Saclay collaboration. From our observed ratio Be-10/Be = 4.3 +/- 1.5% we deduce an average interstellar density of about 0.28 (+0.14, -0.11) atoms/cu cm, and a cosmic-ray lifetime for escape of 27 (+19, -9) x 106 years. The surviving fraction of Be-10 is found to be 0.19 +/- 0.07. Modifications to the conclusions of the Leaky-Box model when a diffusion + convection halo model for propagation is used are also considered.

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