The nuclear method to discover Majorana neutrinos is the neutrinoless double \beta decay. An interesting alternative is offered by the inverse process, neutrinoless radiative double electron capture, accompanied by a photon emission. Two different mechanisms seem plausible: the magnetic type radiation by an initial electron and the resonant electric type radiation by the final atom. The physical background for these processes is calculated.

PACS numbers: 13.15+g, 23.40.Bw