Mass fractions of hydrogen (black line), helium (blue line), CNO group elements (green line), iron group elements except for ⁵⁶Ni (magenta line), and radioactive ⁵⁶Ni (red line) as functions of velocity at day 50 in models B15-2 (panel a)), N20-P (panel b)), W18 (panel c)), and W20 (panel d)) for the late-time 1D simulations. In all models the total ⁵⁶Ni mass is scaled to fit the observed luminosity in the radioactive tail (see Table 4 and Fig. 11).