Radiative relaxation of the slab-center temperature is shown for the reference model. Full line corresponds to hydrogen-calcium mixture, dashed one is for pure hydrogen plasma. Both cases are treated in PRD and are therefore consistent with the results in Table 1 (note that the dashed line can be compared with the corresponding plot in Gouttebroze 2007, the differences are due to geometry and PRD/CRD). In both cases, the relaxation starts from an isothermal slab model with T = 10   000 K.