Supernova prompt neutronization neutrinos and neutrino magnetic moments

It is shown that the combined action of spin-flavour conversions of supernova neutrinos due to the interactions of their Majorana-type transition magnetic moments with the supernova magnetic fields and flavour conversions due to the mass mixing can lead to the transformation of v(e) born in the neutronization process into their antiparticles (v) over bar (e). Such an effect would have a clear experimental signature and its observation would be a 'smoking gun' evidence for the neutrino transition magnetic moments. It would also signify a value of the leptonic mixing parameter \U-e3\ in excess of 10(-2).