Scattering of ultra-cold neutrons (UCN) by superfluid helium at temperatures around 1 K

Kilvington, A.I.; Golub, R.; Mampe, W.; Ageron, P.

doi:10.1016/0375-9601(87)90174-5

Cited by 35 publications

(25 citation statements)

References 9 publications

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confidence: 87%

“…Because 4 He has no nuclear absorption, the only limitations to the density of UCNs accumulated are wall losses and neutron beta decay. The production of UCNs by this process has been observed and agrees with theoretical expectations [14,15,16,17,18].While superfluid 4 He is an excellent superthermal converter, a few other materials, such as solid deuterium (SD 2 ), satisfy the criteria for superthermal production. The limiting UCN density, ρ UCN , one can obtain using a SD 2 source is given by the product of the rate of UCNs production in the solid, R, and the lifetime of UCNs in the solid, τ SD : ρ UCN = Rτ SD .…”

supporting

confidence: 81%

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Measurements of Ultracold-Neutron Lifetimes in Solid Deuterium

Cl¹,

Anaya²,

Tj³

et al. 2002

Phys. Rev. Lett.

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We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD2). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. Superthermal UCN sources offer orders of magnitude improvement in the available densities of UCNs, and are of great importance to fundamental particle-physics experiments such as searches for a static electric dipole moment and lifetime measurements of the free neutron. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time.PACS numbers: 29.25. Dz, 28.20.Gd, 32.80.Pj Neutrons with kinetic energies less than 340 neV (corresponding to a temperature T< 5mK) can be trapped in material bottles and are referred to as ultracold neutrons (UCNs) [1,2,3]. UCN densities at reactor sources have gradually increased with reactor power and improved techniques for extracting the UCN flux. The highest bottled densities reported in the literature, 41/cm 3 , have been obtained at the Institut Laue-Langevin (ILL) reactor in Grenoble [4].Measurements of the neutron electric dipole moment [5,6] and the neutron lifetime [7,8,9] attest to the utility of bottled UCNs for fundamental experiments with neutrons. UCNs may prove useful in improved measurements of angular correlations in neutron beta-decay [10,11], although experiments of this kind utilizing UCNs have not yet been performed. All of these experimental programs have been limited by the available densities of UCNs.Superthermal UCN production, where the production rate of UCNs due to down-scattering in energy is larger than the combined up-scatter and nuclear-absorption rates in the material, was first proposed in 1975 by Golub and Pendlebury [12] in superfluid 4 He and experimentally investigated shortly thereafter [13,14]. In this process phonon creation in the liquid is used to down-scatter cold neutrons to the UCN regime, while up-scattering is suppressed by maintaining the superfluid at sufficiently low temperature. Because 4 He has no nuclear absorption, the only limitations to the density of UCNs accumulated are wall losses and neutron beta decay. The production of UCNs by this process has been observed and agrees with theoretical expectations [14,15,16,17,18].While superfluid 4 He is an excellent superthermal converter, a few other materials, such as solid deuterium (SD 2 ), satisfy the criteria for superthermal production. The limiting UCN density, ρ UCN , one can obtain using a SD 2 source is given by the product of the rate of UCNs production in the solid, R, and the lifetime of UCNs in the solid, τ SD : ρ UCN = Rτ SD . A storage bottle opened to such a source will come into density equilibrium with the density in the solid. This led to the proposal of a thi...

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supporting

confidence: 87%

supporting

confidence: 81%

Measurements of Ultracold-Neutron Lifetimes in Solid Deuterium

Cl¹,

Anaya²,

Tj³

et al. 2002

Phys. Rev. Lett.

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“…This validates an old idea [23] which has long awaited to become converted into a versatile tool. Twenty years ago in a first attempt to accumulate and extract UCN from superfluid 4 He only a small fraction of the UCN could be observed outside the cryostat [26]. As a result, nowadays several projects employ the converter in-situ, thus avoiding UCN extraction from the helium.…”

Section: Discussionmentioning

confidence: 99%

“…This became possible by vertically extracting the UCN through a cold mechanical valve situated above the helium bath. In contrast to a previous attempt to extract accumulated UCN horizontally [26], no loss-prone gaps or windows are required in our method, which now opens the door to apply UCN production in superfluid 4 He for a wide range of experiments and possibly as a user facility. As a first step in this direction an upgrade of the prototype will be installed at an intense monochromatic neutron beam at the ILL in order to feed UCN to an experiment to continue the study of bound quantum states above a flat mirror [27].…”

Section: Introductionmentioning

confidence: 99%

Ultracold neutrons extracted from a superfluid-helium converter coated with fluorinated grease

et al. 2010

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We report experiments on the production of ultracold neutrons (UCN) in a converter of superfluid helium coated with fluorinated grease (fomblin). We employed our special technique of window-free extraction of accumulated UCN from the superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. The fomblin-coating reduced the time constant for UCN passage through the extraction hole by a factor three compared to our previous experiment employing an uncoated stainless steel vessel. A time-of-flight measurement of the cold neutron spectrum incident on the converter, combined with a gold foil activation, allowed us to determine both the single-phonon and multi-phonon contributions to the UCN production. The UCN production rate is in reasonable agreement with the theoretical expectation.

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“…The use of superfluid helium to produce UCN has been demonstrated in several previous experiments [25][26][27][28] and upscattering rates have been measured in Refs. [25] and [28].…”

Section: B Superthermal Production Of Ucnmentioning

confidence: 99%

Magnetic trapping of ultracold neutrons

et al. 2001

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Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with 4 He. Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which 500 ± 155 neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal, 660 s +290 −170 s, is consistent with the neutron beta-decay lifetime.

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Scattering of ultra-cold neutrons (UCN) by superfluid helium at temperatures around 1 K

Cited by 35 publications

References 9 publications

Measurements of Ultracold-Neutron Lifetimes in Solid Deuterium

Measurements of Ultracold-Neutron Lifetimes in Solid Deuterium

Ultracold neutrons extracted from a superfluid-helium converter coated with fluorinated grease

Magnetic trapping of ultracold neutrons

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