Requirements for the optical elements of a spin-resonance energy filter for neutrons at reactor and pulsed source instruments

In this contribution, we evaluate novel applications of an energy band-pass filter for thermal and cold neutron beams. Our proposal is based on the original concept of the Drabkin spin-resonance flipper, which had been considered as a tunable neutron energy filter at reactor sources. The device takes advantage of the fact that the neutron has a magnetic moment, and consists of a wavelength-selective electromagnetic resonator and a supermirror polarizer/analyzer system. We are proposing improvements to the use of the device, making it suitable for time-of-flight experiments at spallation neutron sources. The modifications include utilizing time-dependence in the flipping process and revised magnetic field profiles. Calculations and preliminary results are presented, demonstrating the sensitivity of the device to the efficiency of the polarizing supermirror optics and to the angular divergence of the beam. We will compare the performance of the Drabkin energy filter used in static mode at reactor instruments and in dynamic mode at a pulsed source, and evaluate the potentially achievable wavelength resolution for the case of a reflectometry experiment.