Measurement of spin-flip probabilities for ultracold neutrons interacting with nickel phosphorus coated surfaces

Abstract We report a measurement of the spin-flip probabilities for ultracold neutrons interacting with surfaces coated with nickel phosphorus. For 50 μm thick nickel phosphorus coated on stainless steel, the spin-flip probability per bounce was found to be β NiP on SS = ( 3 . 3 − 5.6 + 1.8 ) × 10 − 6 . For 50 μm thick nickel phosphorus coated on aluminum, the spin-flip probability per bounce was found to be β NiP on Al = ( 3 . 6 − 5.9 + 2.1 ) × 10 − 6 . For the copper guide used as reference, the spin flip probability per bounce was found to be β Cu = ( 6 . 7 − 2.5 + 5.0 ) × 10 − 6 . The results on the nickel phosphorus-coated surfaces may be interpreted as upper limits, yielding β NiP on SS 6.2 × 10 − 6 (90% C.L.) and β NiP on Al 7.0 × 10 − 6 (90% C.L.) for 50 μm thick nickel phosphorus coated on stainless steel and 50 μm thick nickel phosphorus coated on aluminum, respectively. Nickel phosphorus coated stainless steel or aluminum provides a solution when low-cost, mechanically robust, and non-depolarizing UCN guides with a high Fermi potential are needed.