  Gravitational resonance spectroscopy consists in measuring the energy
spectrum of bouncing ultracold neutrons above a mirror by inducing resonant
transitions between different discrete quantum levels. We discuss how to induce
the resonances with a flow through arrangement in the GRANIT spectrometer,
excited by an oscillating magnetic field gradient. The spectroscopy could be
realized in two distinct modes (so called DC and AC) using the same device to
produce the magnetic excitation. We present calculations demonstrating the
feasibility of the newly proposed AC mode.
