Cosmic ray energy loss in the heliosphere: Direct evidence from electron-capture-decay secondary isotopes

Details Cosmic ray energy loss in the heliosphere: Direct evidence from electron-capture-decay secondary isotopes Cosmic ray energy loss in the heliosphere: Direct evidence from electron-capture-decay secondary isotopes

Aug 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.8033n&link_type=abstract

Journal of Geophysical Research, Volume 108, Issue A10, pp. LIS 8-1, CiteID 8033, DOI 10.1029/2003JA009876

Astronomy and Astrophysics

Astrophysics

3

Interplanetary Physics: Cosmic Rays, Interplanetary Physics: Solar Cycle Variations (7536), Solar Physics, Astrophysics, And Astronomy: Solar Activity Cycle (2162), Interplanetary Physics: Interplanetary Magnetic Fields

Scientific paper

Measurements by the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE) spacecraft provide direct evidence that galactic cosmic rays lose energy as a result of their interactions with magnetic fields expanding with the solar wind. The secondary isotopes 49V and 51Cr can decay to 49Ti and 51V, respectively, only by electron capture. The observed abundances of these isotopes are directly related to the probability of attaching an electron from the interstellar medium; this probability decreases strongly with increasing energy around a few hundred MeV/nucleon. At the highest energies observed by CRIS, electron attachment on these nuclides is very unlikely, and thus 49V and 51Cr are essentially stable. At lower energies, attachment and decay do occur. Comparison of the energy dependence of the daughter/parent ratios 49Ti/49V and 51V/51Cr during solar minimum and solar maximum conditions confirms that increased energy loss occurs during solar maximum. This analysis indicates an increase in the modulation parameter φ of about 400 to 700 MV corresponding to an increase in average energy loss for these elements of about 200 to 300 MeV/nucleon.

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