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Two main hypotheses for the origin of Galactic cosmic rays are the"supernova" and "superbubble" origin hypotheses. We analyse the evidence forthe superbubble hypothesis provided by the measurements of the relativiveabundances of isotopes of cobalt and nickel in the cosmic ray flux. We comparethe measured upper limit on the abundance of 59Ni in the cosmic ray flux withthe 59Ni abundance predictions of the up-to-date stellar evolution models.Non-detection of 59Ni in the cosmic ray flux has previously been attributed toa large time delay of the order of 1e5 yr between the moment of supernovaexplosion and the onset of particle acceleration process. This large time delaywas considered as an argument in favour of the "superbubble" scenario. We showthat the recent calculation of the 59Ni yield of massive stars, which takesinto account the initial mass range up to 120 solar masses and includes stellarrotation, results in prediction of low 59Ni abundance relative to its decayproduct 59Co. The predicted abundance is consistent with the upper bound on59Ni abundance in the cosmic ray flux for the supernova parameters assumed.This result removes the necessity of decay of 59Ni in the time interval betweenthe supernova explosion and the onset of acceleration process and restores theconsistency of measurements of 59Ni / 59Co abundances with the "supernova"hypothesis of the CR origin.

Abundances of 59Co and 59Ni in the cosmic ray flux