On the Low Energy Decrease in Galactic Cosmic Ray Secondary/Primary Ratios
Abstract
Galactic cosmic ray (GCR) secondary/primary ratios such as B/C and (Sc+Ti+V)/Fe are commonly used to determine the mean amount of interstellar material through which cosmic rays travel before escaping from the Galaxy (Λesc). These ratios are observed to be energy-dependent, with a relative maximum at ∼1 GeV/nucleon, implying a corresponding peak in Λesc. The decrease in Λ_(esc) at energies above 1 GeV/nucleon is commonly taken to indicate that higher energy cosmic rays escape more easily from the Galaxy. The decrease in Λ_(esc) at energies <1 GeV/nuc is more controversial; suggested possibilities include the effects of a galactic wind or the effects of distributed acceleration of cosmic rays as they pass through the interstellar medium. We consider two possible explanations for the low energy decrease in Λ_(esc) and attempt to fit the combined, high-resolution measurements of secondary/primary ratios from ∼0.1 to 35 GeV/nuc made with the CRIS instrument on ACE and the C2 experiment on HEAO-3. The first possibility, which hypothesizes an additional, local component of low-energy cosmic rays that has passed through very little material, is found to have difficulty simultaneously accounting for the abundance of both B and the Fe-secondaries. The second possibility, suggested by Soutoul and Ptuskin, involves a new form for Λ_(esc) motivated by their diffusion-convection model of cosmic rays in the Galaxy. Their suggested form for Λ_(esc)(E) is found to provide an excellent fit to the combined ACE and HEAO data sets.
Additional Information
© 2000 American Institute of Physics. Published online 15 September 2000. This research supported by NASA at Caltech (grant NAG5-6912), JPL, NASA/OSFC, and Washington U.Attached Files
Published - 2000-33.pdf
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Additional details
- Eprint ID
- 55023
- Resolver ID
- CaltechAUTHORS:20150219-135833866
- NASA
- NAG5-6912
- Created
-
2015-02-23Created from EPrint's datestamp field
- Updated
-
2021-11-10Created from EPrint's last_modified field
- Caltech groups
- Space Radiation Laboratory
- Series Name
- AIP Conference Proceedings
- Series Volume or Issue Number
- 528
- Other Numbering System Name
- Space Radiation Laboratory
- Other Numbering System Identifier
- 2000-33