Age of the galactic cosmic rays derived from the abundance of /sup 10/Be

Journal Article · Tue Nov 01 04:00:00 EST 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155632· OSTI ID:5280155

Garcia-Munoz, M; Mason, G M; Simpson, J A

The isotopic composition of galactic cosmic-ray beryllium has been measured in the energy interval 30--150 MeV per nucleon with the use of cosmic-ray telescopes carried on the IMP-7 and IMP-8 Earth satellites during 1973--1975. From the calibration of an identical instrument in beams of /sup 7/Be, /sup 9/Be, and /sup 10/Be at the LBL Bevatron accelerator, it is shown that these instruments can resolve these isotopes and that the calibration determines the relative separation of the /sup 9/Be and /sup 10/Be distributions to an accuracy of +- 0.1 atomic mass units. The measured cosmic-ray isotopic abundances of /sup 7/Be and /sup 9/Be are found to be in agreement with calculations based on steady-state models for the interstellar propagation of cosmic-ray nuclei with an exponential path length distribution with a 6 g cm/sup -2/ leakage mean free path, after account has been taken of solar modulation. However, the measured abundance of the radioactive /sup 10/Be component (half-life=1.5 x 10/sup 6/ years) is substantially less than that calculated under the assumption that the cosmic rays propagate in regions of the galactic disk that have the traditionally accepted average interstellar density of 1 atom cm/sup -3/. From our observed ratio /sup 10/Be/Be=0.028 +- 0.014, we deduce an average interstellar density of about 0.2 atoms cm/sup -3/, and a cosmic-ray lifetime for escape of 1.7 x 10/sup 7/ years. The most obvious conclusion to be drawn from the experiments is that, since the average interstellar matter density traversed by the cosmic rays is smaller than the average densities derived from the current observational evidence for the galactic disk, the cosmic rays may be spending the major part of their life in the galactic halo or in specific regions of the disk with low matter density. We discuss the implications of this low interstellar density for models of the confinement and propagation of the cosmic rays in galactic magnetic fields.

• Research Organization: Enrico Fermi Institute, University of Chicago
• OSTI ID: 5280155
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 217:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

654001* -- Radiation & Shielding Physics-- Radiation Physics
Shielding Calculations & Experiments
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ABUNDANCE
ACCELERATORS
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
BERYLLIUM 10
BERYLLIUM ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BEVATRON
CHEMICAL COMPOSITION
COSMIC GASES
COSMIC NUCLEI
COSMIC RADIATION
CYCLIC ACCELERATORS
EVEN-EVEN NUCLEI
FLUIDS
GALAXIES
GASES
IONIZING RADIATIONS
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MILKY WAY
NUCLEAR REACTIONS
NUCLEI
PRIMARY COSMIC RADIATION
RADIATIONS
RADIOISOTOPES
SYNCHROTRONS
TELESCOPE COUNTERS
YEARS LIVING RADIOISOTOPES