Radioactive mechanism for the late time luminosity of the type 2 supernovae and ionization of hydrogen

The ionization of the hydrogen in the type 2 supernova SN 1970 g at the late time (t ∼ 270 days) is studied assuming that the supernova luminosity is powered by the radioactive decay 56Co → 56Fe. The ionization balance of the hydrogen is calculated with all relevant processes taken into account. It is shown that a) nonthermal ionization itself is inadequate; b) when thermal ionization being taken into account the required ionization degree is reached at Te ∼ 7000 K; c) main process of the hydrogen ionization is the photoionization from the level n=2 by Mg2 λ2798 quanta. We predict the intensity of the emission line of Mg2 λ2798 in the late time spectra of SN 2 comparable with that of Hα line