  Electron capture (EC) isotopes are known to provide constraints on the low
energy behavior of cosmic rays (CRs), such as re-acceleration. Here we study
the EC isotopes within the framework of the dynamic spiral-arms CR propagation
model in which most of the CR sources reside in the galactic spiral arms. The
model was previously used to explain the B/C and sub-Fe/Fe ratios
\citep{BoverC,Iron}. We show that the known inconsistency between the
$^{49}$Ti/$^{49}$V and $^{51}$V/$^{51}$Cr ratios remains also in the
spiral-arms model. On the other hand, unlike the general wisdom in which the
isotope ratios depend primarily on reacceleration, we find here that the ratio
also depends on the halo size ($z_\mathrm{h}$) and in spiral-arms models also
on the time since the last spiral arm passage ($\tau_\mathrm{arm}$). Namely, EC
isotopes can in principle provide interesting constraints on the diffusion
geometry. However, with the present uncertainties in the lab measurements of
both the electron attachment rate and the fragmentation cross-sections, no
meaningful constraint can be placed.
