  Cosmic ray (CR) sources leave signatures in the isotopic abundances of CRs.
Current models of Galactic CRs that consider supernovae (SNe) shocks as the
main sites of particle acceleration cannot satisfactorily explain the higher
${\rm ^{22}Ne/^{20}Ne}$ ratio in CRs compared to the interstellar medium.
Although stellar winds from massive stars have been invoked, their contribution
relative to SNe ejecta has been taken as a free parameter. Here we present a
theoretical calculation of the relative contributions of wind termination
shocks (WTSs) and SNe shocks in superbubbles, based on the hydrodynamics of
winds in clusters, the standard stellar mass function, and stellar evolution
theory. We find that the contribution of WTSs towards the total CR production
is at least $25\%$, which rises to $\gtrsim 50\%$ for young ($\lesssim 10$ Myr)
clusters, and explains the observed $^{22}{\rm Ne}/^{20} {\rm Ne}$ ratio. We
argue that since the progenitors of apparently isolated supernovae remnants
(SNRs) are born in massive star clusters, both WTS and SNe shocks can be
integrated into a combined scenario of CRs being accelerated in massive
clusters. This scenario is consistent with the observed ratio of SNRs to
$\gamma$-ray bright ($L_\gamma \gtrsim 10^{35}$ erg s$^{-1}$) star clusters, as
predicted by star cluster mass function. Moreover, WTSs can accelerate CRs to
PeV energies, and solve other longstanding problems of the standard supernova
paradigm of CR acceleration.
