Losses and depolarization of ultracold neutrons on neutron guide and storage materials

At Institut Laue-Langevin (ILL) and Paul Scherrer Institute (PSI), we have measured the losses and depolarization probabilities of ultracold neutrons on various materials: (i) nickel-molybdenum alloys with weight percentages of 82/18, 85/15, 88/12, 91/9, and 94/6 and natural nickel Ni100, (ii) nickel-vanadium NiV93/7, (iii) copper, and (iv) deuterated polystyrene (dPS). For the different samples, storage-time constants up to $\ensuremath{\sim}460\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ were obtained at room temperature. The corresponding loss parameters for ultracold neutrons, $\ensuremath{\eta}$, varied between $1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. All $\ensuremath{\eta}$ values are in agreement with theory except for dPS, where anomalous losses at room temperature were established with four standard deviations. The depolarization probabilities per wall collision $\ensuremath{\beta}$ measured with unprecedented sensitivity varied between $0.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and $9.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Our depolarization result for copper differs from other experiments by 4.4 and 15.8 standard deviations. The $\ensuremath{\beta}$ values of the paramagnetic NiMo alloys over molybdenum content show an increase of $\ensuremath{\beta}$ with increasing Mo content. This is in disagreement with expectations from literature. Finally, ferromagnetic behavior of NiMo alloys at room temperature was found for molybdenum contents of 6.5 at.% or less and paramagnetic behavior for more than 8.7 at.%. This may contribute to solving an ambiguity in literature.