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

Abstract : 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 ∼ 460 s were obtained at room temperature. The corresponding loss parameters for ultracold neutrons, η , varied between 1.0 × 10 − 4 and 2.2 × 10 − 4 . All η 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 β measured with unprecedented sensitivity varied between 0.7 × 10 − 6 and 9.0 × 10 − 6 . Our depolarization result for copper differs from other experiments by 4.4 and 15.8 standard deviations. The β values of the paramagnetic NiMo alloys over molybdenum content show an increase of β 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.
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Submitted on : Thursday, November 23, 2017 - 10:50:26 AM
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V. Bondar, S. Chesnevskaya, M. Daum, B. Franke, P. Geltenbort, et al.. Losses and depolarization of ultracold neutrons on neutron guide and storage materials. Phys.Rev.C, 2017, 96 (3), pp.035205. ⟨10.1103/PhysRevC.96.035205⟩. ⟨hal-01645840⟩

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