Evolution of the SN remnants of two rotating stars of initial masses 20 M_⊙ (dotted) and 60 M_⊙ (solid), respectively. Top: velocity of the forward shock and swept-up mass. Middle: shock radius and density profile before shock arrival (see text). Bottom: composition of the matter swept up up to time t by the shock wave, for the ¹⁴N/¹⁶O and ²²Ne/²⁰Ne ratios. In all panels, the thickportions of the curves indicate the period of efficient particle acceleration, i.e. from the beginning of the ST phase and as far as υ_s > υ_min. The value of υ_min (=1900 km s^-1 for the rotating star models in the figure) is chosen so that the IMF averaged theoretical ratio of ²²Ne/²⁰Ne matches the observed one in GCR (see text, Eq. (13) and Fig. 6).