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Direct Evidence of Energy-Loss in Electron-Capture-Decay Secondary Isotopes in the Heliosphere

Scott, L. M. and Davis, A. J. and Wiedenbeck, M. E. and Binns, W. R. and Christian, E. R. and Cummings, A. C. and George, J. S. and Hink, P. L. and Israel, M. H. and Leske, R. A. and Mewaldt, R. A. and Niebur, S. M. and Stone, E. C. and von Rosenvinge, T. T. and Yanasak, N. E. (2003) Direct Evidence of Energy-Loss in Electron-Capture-Decay Secondary Isotopes in the Heliosphere. In: Proceedings of the 28th International Cosmic Ray Conference. Vol.7. International Union of Applied Physics , Tokyo, Japan, pp. 3811-3814.

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We report direct evidence of the energy loss of galactic cosmic rays as they diffuse in magnetic irregularities expanding with the solar wind. Using the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE), we report on the energy-dependence of the electron-capture decay of the secondary isotopes ^(49)V and ^(51)Cr. At the highest energies observed by CRIS, where electron attachment is unlikely, ^(49)V and ^(51)Cr are essentially stable; at lower energies the timescale for electron attachment is much shorter and substantial decay does occur. Comparing the energy dependence of the daughter/parent ratios ^(49)Ti/^(49)V and ^(51)V/^(51)Cr during periods of solar minimum and maximum demonstrates that the solar modulation parameter φ is about 400 to 700 MV higher during solar maximum than at minimum. Absolute values of φ inferred from these electron-capture-isotope data agree well with values inferred from comparison of the observed elemental energy spectra with model calculations.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Wiedenbeck, M. E.0000-0002-2825-3128
Binns, W. R.0000-0001-6110-3407
Christian, E. R.0000-0003-2134-3937
Cummings, A. C.0000-0002-3840-7696
Israel, M. H.0000-0002-8104-208X
Leske, R. A.0000-0002-0156-2414
Mewaldt, R. A.0000-0003-2178-9111
Stone, E. C.0000-0002-2010-5462
Additional Information:Copyright Universal Academy Press Inc. This research was supported by NASA grants NAG5-6912 and NAG5-12929 to the California Institute of Technology and by related grants to the Jet Propulsion Laboratory, the Goddard Space Flight Center, and Washington University.
Group:Space Radiation Laboratory
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Space Radiation Laboratory2003-19
Record Number:CaltechAUTHORS:20150406-141916278
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56390
Deposited By: Deborah Miles
Deposited On:15 Apr 2015 03:22
Last Modified:09 Mar 2020 13:19

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