Losses and depolarization of ultracold neutrons on neutron guide and storage materials
2017
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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