  We analyze the problem of neutrino oscillations via a fermionic particle
detector model inspired by the physics of the Fermi theory of weak
interactions. The model naturally leads to a description of emission and
absorption of neutrinos in terms of localized two-level systems. By explicitly
including source and detector as part of the dynamics, the formalism is shown
to recover the standard results for neutrino oscillations without mention to
"flavor states", which are ill defined in quantum field theory. This
illustrates how particle detector models provide a powerful theoretical tool to
approach the measurement issue in quantum field theory and emphasizes that the
notion of flavor states, although sometimes useful, must not play any crucial
role in neutrino phenomenology.
