  Neutron guides are used to transport slow neutrons from sources to
experiments. Conventional neutron supermirror guides use alternating thin
layers based on nickel and titanium. Due to the magnetic properties of nickel,
their neutron reflection properties are spin-dependent, in particular when
exposed to high magnetic fields. Motivated by the requirements of precision
experiments on neutron beta decay, we present novel supermirrors based on
copper and titanium, which preserve the neutron beam polarization. These show
excellent reflectivity and prove to be very stable even when exposed to high
temperatures.
