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~$\hat{I}¼$m thick nickel phosphorus coated on stainless steel, the spin-flip probability per bounce was found to be ${\hat{I}}_{\mathrm{NiP}\mathrm{on}\mathrm{SS}}^2=(3.3_{-5.6}^{+1.8})\times 10^{-6}$. For 50~$\hat{I}¼$m thick nickel phosphorus coated on aluminum, the spin-flip probability per bounce was found to be ${\hat{I}}_{\mathrm{NiP}\mathrm{on}\mathrm{Al}}^2=(3.6_{-5.9}^{+2.1})\times 10^{-6}$. For the copper guide used as reference, the spin flip probability per bounce was found to be ${\hat{I}}_{\mathrm{Cu}}^2=(6.7_{-2.5}^{+5.0})\times 10^{-6}$. The results on the nickel phosphorus-coated surfaces may be interpreted as upper limits, yielding ${\hat{I}}_{\mathrm{NiP}\mathrm{on}\mathrm{SS}}^2<6.2\times 10^{-6}$ (90\% C.L.) and ${\hat{I}}_{\mathrm{NiP}\mathrm{on}\mathrm{Al}}^2<7.0\times 10^{-6}$ (90\% C.L.) for 50~$\hat{I}¼$m thick nickel phosphorus coated on stainless steel and 50~$\hat{I}¼$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.

12 pages, 5 figures