Magnetron-sputtered Be coatings as reflectors for ultracold neutrons

Bryś, T.; Daum, M.; Fierlinger, P.; Fomin, A. K.; Geltenbort, P.; Henneck, R.; Kirch, K.; Харитонов, А. Г.; Krasnoshekova, I.; Kuźniak, M.; Lasakov, M. S.; Pichlmaier, A.; Raimondi, Fabio; Schelldorfer, R.; Serebrov, A. P.; Siber, E.; Tal'Daev, R. R.; Varlamov, V. E.; Vasiliev, A. V.; Wambach, J.; Zherebtsov, O. M.

doi:10.1016/j.nima.2005.06.063

Cited by 9 publications

(5 citation statements)

References 22 publications

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“…In the case of dPS, where one expects an extremely low loss factor (W/V f = 0.0016 × 10 −4 ), the difference is three orders of magnitude. This difference, previously termed anomalous losses, is attributed to, e.g., impurities, low-energy heating, surface contaminations or microscopic holes in the coating, and contaminations of the surface with hydrogen [65][66][67]96,97]. The data also show that there is no dependence on energy, as expected.…”

Section: B the Wall Loss Parameter ηsupporting

confidence: 68%

“…Their optical potentials, V f , and other material parameters were determined [59]: V f (dPS) = (161 ± 10) neV and V f (dPE) = (214 ± 10) neV. The UCN losses at room temperature for dPS, η = (3 ± 1) × 10 −4 [59], were similar to those of commonly used materials for UCN storage, e.g., diamond-like carbon (DLC) or beryllium [48] with optical potentials around 250 neV [46,48,49,[60][61][62][63] and low losses [52,[64][65][66][67]. In the nEDM experiment at PSI [7], the high-voltage electrodes of the present chamber are coated with DLC while the walls are coated with dPS, which has the limiting optical potential V f of the apparatus.…”

Section: Ucn Losses and Depolarization From Surfacesmentioning

confidence: 94%

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

et al. 2017

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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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Section: B the Wall Loss Parameter ηsupporting

confidence: 68%

Section: Ucn Losses and Depolarization From Surfacesmentioning

confidence: 94%

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

et al. 2017

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“…For the Be coatings produced at PNPI we obtained F H = (1-2) × 10 −4 [40]; the value for the DLC(Al-foil) was F H = (1-2) × 10 −4 and for…”

Section: Samplesmentioning

confidence: 84%

Loss and spinflip probabilities for ultracold neutrons interacting with diamondlike carbon and beryllium surfaces

et al. 2007

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The storage of ultracold neutrons (UCN) in a combined magnetic, gravitational, and material trap is described. Wall materials investigated were diamondlike carbon (DLC) coatings on solid and flexible foil substrates as well as beryllium coatings on solid substrates. The loss coefficient per wall collision, η, and the depolarization probability β were measured simultaneously as a function of temperature (from 70 to 400 K) and energy (from 30 to 80 neV). The results at 70 K are η = (0.7 ± 0.1) × 10 −4 , β = (15.4 ± 1.0) × 10 −6 for DLC on polyethyleneterephtalate (PET) foil and η = (1.7 ± 0.1) × 10 −4 , β = (0.7 ± 0.3) × 10 −6 for DLC on aluminum foil. At room temperature the loss coefficients are larger by a factor of about 2 whereas the depolarization probabilities are found to be independent of temperature. The corresponding values for Be at room temperature are η ∼ 5 × 10 −4 , β ∼ 10 × 10 −6 . The DLC results for β and for the temperature-dependent part of the loss coefficient, η T , are interpreted in terms of incoherent scattering by hydrogen. The hydrogen admixture was measured independently by elastic recoil detection analysis to be about 1 × 10 16 atoms/cm 2 . The data do not support the hypothesis of hydrogen being chemically bound within the top layers of the DLC. Using two different models with a thin waterlike film on top of the substrate we obtain consistency between the temperature-dependent loss contribution and the measured hydrogen contamination.

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“…V = V = 252 neV). Beryllium has become a standard material for UCN trapping, with a best reported experimental value of f = 3 × 10 −5 in the low temperature limit [83,84], despite a much smaller theoretical value (the finding that this was never reached was termed "anomalous losses" and has triggered many experimental investigations and speculations). However, it might be more realistic to consider also worse values for f , assuming that efficient cleaning procedures cannot be applied in situ (e.g.…”

Section: Saturated Ucn Densitymentioning

confidence: 99%

Ultracold neutron accumulation in a superfluid-helium converter with magnetic multipole reflector

Zimmer

Golub

2015

Phys. Rev. C

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We analyze accumulation of ultracold neutrons (UCN) in a superfluid-helium converter vessel surrounded by a magnetic multipole reflector. We solved the spin-dependent rate equation, employing formulas valid for adiabatic spin transport of trapped UCN in mechanical equilibrium. Results for saturation UCN densities are obtained in dependence of order and strength of the multipolar field. The addition of magnetic storage to neutron optical potentials can increase the density and energy of the low field seeking UCN produced and serves to mitigate the effects of wall losses on the source performance. It also can provide a highly polarized sample of UCN without need to polarize the neutron beam incident on the converter. This work was performed in preparation of the UCN source project SuperSUN at the ILL.

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Magnetron-sputtered Be coatings as reflectors for ultracold neutrons

Cited by 9 publications

References 22 publications

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

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

Loss and spinflip probabilities for ultracold neutrons interacting with diamondlike carbon and beryllium surfaces

Ultracold neutron accumulation in a superfluid-helium converter with magnetic multipole reflector

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