Th. Betz, G. Badurek, E. Jericha:
"Quantum mechanical aspects of dynamical neutron polarization";
Physica B: Condensed Matter,
DYNAMIC NEUTRON POLARIZATION (DNP) is a concept which allows to achieve complete polarization of slow neutrons, virtually
without any loss of intensity. There the neutrons pass through a combination of a static and a rotating magnetic field in resonance, like in
a standard NMR apparatus. Depending on their initial spin state, they end up with different kinetic energies and therefore different
velocity. In a succeeding magnetic precession field this distinction causes a different total precession angle. Tuning the field strength can
lead to a final state where two original anti-parallel spin states are aligned parallel and hence to polarization.
The goal of this work is to describe the quantum mechanical aspects of DNP and to work out the differences to the semi-classical
treatment. We show by quantum mechanical means, that the concept works and DNP is feasible, indeed. Therefore, we have to take a
closer look to the behavior of neutron wave functions in magnetic fields. In the first Section we consider a monochromatic continuous
beam. The more realistic case of a pulsed, polychromatic beam requires a time-dependent field configuration and will be treated in the
second Section. In particular the spatial separation of the spin up- and down-states is considered, because it causes an effect of
polarization damping so that one cannot achieve a fully polarized final state. This effect is not predicted by the semi-classical treatment of
DNP. However, this reduction of polarization is very small and can be neglected in realistic DNP-setups.
Erstellt aus der Publikationsdatenbank der Technischen Universitšt Wien.