Davis, A. J. and Mewaldt, R. A. and Binns, W. R. and Christian, E. R. and Cummings, A. C. and George, J. S. and Hink, P. L. and Leske, R. A. and von Rosenvinge, T. T. and Wiedenbeck, M. E. and Yanasak, N. E. (2000) On the Low Energy Decrease in Galactic Cosmic Ray Secondary/Primary Ratios. In: Acceleration and Transport of Energetic Particles Observed in the Heliosphere. AIP Conference Proceedings. No.528. American Institute of Physics , Melville, N.Y., pp. 421-424. ISBN 1-56396-951-3 http://resolver.caltech.edu/CaltechAUTHORS:20111123-142326519
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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 (Λ_(esc)). These ratios are observed to be energy-dependent, with a relative maximum at ~1 GeV/nucleon, implying a corresponding peak in Λ_(esc). 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.
|Item Type:||Book Section|
|Additional Information:||© 2000 American Institute of Physics. Issue Date: 15 September 2000. This research supported by NASA at Caltech (grant NAG5-6912), JPL, NASA/GSFC, and Washington U.|
|Group:||Space Radiation Laboratory|
|Subject Keywords:||galactic cosmic rays, cosmic ray composition, element relative abundance, transport processes, interstellar matter, cosmic ray propagation, cosmic ray energy spectra|
|Classification Code:||PACS: 98.70.Sa; 96.40.De|
|Official Citation:||On the low energy decrease in galactic cosmic ray secondary/primary ratios A. J. Davis, R. A. Mewaldt, W. R. Binns, E. R. Christian, A. C. Cummings, J. S. George, P. L. Hink, R. A. Leske, T. T. von Rosenvinge, M. E. Wiedenbeck, and N. E. Yanasak, AIP Conf. Proc. 528, 421 (2000), DOI:10.1063/1.1324351|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||23 Nov 2011 22:48|
|Last Modified:||04 Mar 2013 17:49|
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