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Description
Commonly used UCN beam polarizers employ the longitudinal Stern-Gerlach effect due to a strong magnetic field, or spin dependent neutron transmission through a thin magnetized foil, exploiting the combination of the spin independent neutron optical potential and the spin dependent magnetic potential. In contrast to commonly used iron foils, the commercial alloy Hiperco50, consisting of 49% iron, 49% cobalt and 2% vanadium, has nearly matched nuclear and saturated magnetic potentials of 130 neV and +/-139 neV, respectively. It should therefore be able to polarize UCN down to zero energy even in reflection. First tests of this concept were performed using various prototypes in the standard polarizer/spin-flipper/analyzer configuration installed at ILL’s UCN sources PF2 and SUN. At PF2, time-of-flight analysis with a chopper demonstrated neutron polarization for a wide spectrum, including neutron energies far beyond the UCN range. At SUN, spectrally integrated flipping ratios larger than five were measured using annealed foils. A second generation of devices is being prepared for a second beam time in autumn 2025.
