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

TL;DR

This study measures the spin-flip probabilities of ultracold neutrons interacting with nickel phosphorus coated surfaces, providing upper limits and implications for UCN guide design.

Contribution

It presents the first measurements of spin-flip probabilities for ultracold neutrons on nickel phosphorus coated surfaces, establishing upper limits for these probabilities.

Findings

Spin-flip probability for NiP on stainless steel: <6.2×10^{-6} (90% C.L.)

Spin-flip probability for NiP on aluminum: <7.0×10^{-6} (90% C.L.)

Reference copper guide has higher spin-flip probability: 6.7×10^{-6}

Abstract

We report a measurement of the spin-flip probabilities for ultracold neutrons interacting with surfaces coated with nickel phosphorus. For 50~$\mu$m thick nickel phosphorus coated on stainless steel, the spin-flip probability per bounce was found to be $\beta_{\rm NiP\;on\;SS} = (3.3^{+1.8}_{-5.6}) \times 10^{-6}$. For 50~$\mu$m thick nickel phosphorus coated on aluminum, the spin-flip probability per bounce was found to be $\beta_{\rm NiP\;on\;Al} = (3.6^{+2.1}_{-5.9}) \times 10^{-6}$. For the copper guide used as reference, the spin flip probability per bounce was found to be $\beta_{\rm Cu} = (6.7^{+5.0}_{-2.5}) \times 10^{-6}$. The results on the nickel phosphorus-coated surfaces may be interpreted as upper limits, yielding $\beta_{\rm NiP\;on\;SS} < 6.2 \times 10^{-6}$ (90\% C.L.) and $\beta_{\rm NiP\;on\;Al} < 7.0 \times 10^{-6}$ (90\% C.L.) for 50~$\mu$m thick nickel phosphorus coated on stainless steel and 50~$\mu$m 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.