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Astron. Astrophys. 336, L61-L64 (1998)

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Letter to the Editor

Evidence from Voyager and ISEE-3 spacecraft

Data for the decay of secondary K-electron capture isotopes during the propagation of cosmic rays in the Galaxy

A. Soutoul 1, R. Legrain 1, A. Lukasiak 2, F.B. McDonald 2 and W.R. Webber 3

1 DAPNIA/SAp,SPhN CEA/SACLAY, F-91191 Gif-sur-Yvette CEDEX, France
2 Institute for Physical Sciences and Technology, University of Maryland
3 Astronomy Department New Mexico State University, Las Cruces, NM

Received 31 July 1997 / Accepted 12 May 1998


New data from the cosmic ray experiment on the Voyager spacecraft confirms and extends earlier data from a similar experiment on the ISEE-3 spacecraft which indicates the possibility of the decay of certain K-capture isotopes during the interstellar propagation of galactic cosmic rays. These cosmic ray measurements, along with the cross section measurements, indicate that [FORMULA] 25% of the K-capture isotopes 51Cr and 49V produced as secondaries have decayed at interstellar energy of [FORMULA] 400 MeV/nuc. This suggests a possible interstellar energy gain [FORMULA] 100 MeV/nuc out of the current interstellar energy [FORMULA] 500 MeV/nuc. This measurement suggests that the study of the K-capture isotopes may now have reached a level that will soon provide definitive information on the amount of re-acceleration that may occur during cosmic-ray propagation after an initial acceleration in the cosmic ray sources.

Key words: ISM: cosmic rays

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998