  Leptogenesis is studied within the seesaw neutrino mass model in a regime
where all sterile neutrinos have prompt rather than delayed decays. It is shown
that during neutrino thermal production lepton asymmetries are generated in
both active lepton and sterile neutrino sectors. The large B-L asymmetry is
slowly pumped into the chemically decoupled right-handed quarks and leptons and
baryon number sector which later protect B-L from fast L violating processes.
The dependence of the final baryon asymmetry on couplings and masses is totally
different from the decay scenario. B does not vanish in the limit of degenerate
light neutrinos and the observed asymmetry is naturally obtained for a sum of
square masses between the atmospheric neutrino mass gap and 0.2 eV^2.
