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

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

Physics Letters A

Volume 125, Issue 8, 30 November 1987, Pages 416-420

https://doi.org/10.1016/0375-9601(87)90174-5 Get rights and content

Abstract

We report the first observation of the upscattering of UCN stored in a closed vessel filled with ⁴He. The observations allow the direct determination of the production rate and hence the density of the UCN stored in the helium, which are found to be in agreement with theoretical expectations. the technique offers the possibility of studying the interactions between excitations in the liquid at regions of temperature and wavelength inaccessible to presently available methods.

References (14)

R. Golub et al.
Phys. Lett. A
(1975)
R. Golub et al.
Phys. Lett. A
(1977)
R. Golub
Nucl. Instrum. Methods
(1984)
R. Golub
Phys. Lett. A
(1979)
P. Ageron et al.
Phys. Lett. A
(1978)
P.C. Hendry et al.
Cryogenics
(1987)
P. Ageron et al.
Phys. Lett. A
(1978)

There are more references available in the full text version of this article.

Cited by (41)

Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT
2009, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
The gravitational spectrometer GRANIT will be set up at the Institut Laue Langevin. It will profit from the high ultracold neutron density produced by a dedicated source. A monochromator made of crystals from graphite intercalated with potassium will provide a neutron beam with 8.9 Å incident on the source. The source employs superthermal conversion of cold neutrons in superfluid helium, in a vessel made from BeO ceramics with Be windows. A special extraction technique has been tested which feeds the spectrometer only with neutrons with a vertical velocity component $v_{⊥} \leq 20 cm s^{- 1}$ , thus keeping the density in the source high. This new source is expected to provide a density of up to $ρ = 800 {cm}^{- 3}$ for the spectrometer.
Neutron multigroup cross-sections of moderator materials for cold and ultracold neutron production
2007, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
A total of 32 sets of multigroup (energy-averaged) cross-sections are developed for liquid ⁴He, $H_{2}$ , $D_{2}$ , ${CH}_{4}$ , $H_{2} O$ and $D_{2} O$ and solid ${CH}_{4}$ at widely different temperatures. The neutron energy range from 10 MeV down to $0.1 μ eV$ is covered. It is intended to treat both the moderation of fission and spallation neutrons and the production of low-energy neutrons such as thermal $(\sim 25 meV)$ , cold $(\sim 2 meV)$ and ultracold ( $<$ about $0.3 μ eV$ ) neutrons. The entire energy range is divided into 140 intervals (groups) and the angular distribution of scattering is represented by the expansion in Legendre polynomials up to order 3. The cross-sections characterizing low-energy neutron scattering are calculated using the physical models of molecular dynamics and structure for each moderator material. To demonstrate availability of the cross-section sets, a study is made of ultracold neutron production and storage in a liquid- ⁴He sphere surrounded with liquid $D_{2}$ and $D_{2} O$ as reflectors. It is shown that the relevant cross-sections are successful in describing neutron energy spectra for fast and low-energy neutrons and that the study of a liquid-⁴He source clarifies neutronic conditions to be required on the high-density storage of ultracold neutrons. The latter results serve physical and quantitative interpretation of the recent experimental measurement of ultracold neutron production in superfluid ⁴He.
Experimental measurement of ultracold neutron production in superfluid 4He
2003, Physics Letters, Section A: General, Atomic and Solid State Physics
The absolute production rate of ultracold neutrons (UCN) produced by the interaction of a cold neutron beam with superfluid helium has been measured over an incident energy range of 0.7 to 4 meV. The neutrons are reduced in energy to become UCN by creating phonon(s) in the superfluid. The separate roles played by single and multi-phonon emission processes have been identified. Detection and identification of UCN, those neutrons with energies less than ∼250 neV and which can be stored in material bottles, were carried out using solid-state silicon detectors set within the superfluid helium. With a cold neutron flux of 2.62×10⁷ neutrons $cm^{−2} s^{−1} A ̊^{−1}$ at 8.9 Å in the superfluid, the single-phonon production rate of UCN was measured to be (0.91±0.13) $cm^{−3} s^{−1},$ a value close to theoretical prediction. Multi-phonon emission processes for UCN production by higher energy neutrons were also observed and, in the beam used for this work at ILL, they contributed (24±2)% to the overall UCN production rate.
Production of UCN by downscattering in superfluid He4
2002, Physics Letters, Section A: General, Atomic and Solid State Physics
Ultra-Cold Neutrons (UCN) are neutrons with energies so low they can be stored in material bottles and magnetic traps. They have been used to provide the currently most accurate experiments on the neutron life time and electric dipole moment. UCN can be produced in superfluid Helium at significantly higher densities than by other methods. The predominant production process is usually by one phonon emission which can only occur at a single incident neutron energy because of momentum and energy conservation. However UCN can also be produced by multiphonon processes. It is the purpose of this work to examine this multiphonon production of UCN. We look at several different incident neutron spectra, including cases where the multiphonon production is significant, and see how the relative importance of multiphonon production is influenced by the incident spectrum.
Neutronic study of UCN production and storage in a liquid 4He source
2002, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
The production and storage of ultracold neutrons(UCNs) in liquid ⁴He are evaluated by means of a multigroup neutron transport analysis. Several sets of group constants for eight different temperatures between 0.1 and $2.5 K$ in a neutron energy region of $0.1 μeV$ to $10 eV$ are generated. A model UCN source of pure liquid ⁴He is analyzed, in which UCNs are produced by down-scattering of cold neutrons, stored optically by total reflection at the surface, and destroyed by the neutron β-decay only. The following results are obtained: (a) As lowering temperature below about $0.5 K$ , UCN density exhibits saturation behavior because of no significant up-scattering of UCNs. (b) In addition to single down-scattering of a $1 meV$ neutron, multiple scattering of a higher-energy neutron contributes largely to UCN production, nearly doubling UCN density. (c) A high reflection coefficient of, say, greater than 0.9999, is necessary to yield a high UCN density of $1.21×10^{5} cm^{−3}$ at $0.1 K$ .
Quantitative evaluation of ultracold neutron production and storage in superfluid helium
2001, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
The production of ultracold neutron (UCN) in superfluid ⁴He is evaluated by use of the scattering cross-section model of liquid ⁴He developed by the authors in a wide range of temperatures from 0.1 to $4.2 K$ and neutron energies from $0.1 μeV$ to $10 eV$ . Typical results on the total cross section and angular distribution of UCN production are presented. The UCN density attainable in liquid ⁴He is estimated and found to exhibit saturation behavior at lower temperatures. It is shown that $1 meV$ neutrons serve for the UCN production effectively and that the UCN density reaches the maximum of $4.2×10^{4} cm^{−3}$ below about $0.5 K$ where no significant up-scattering of UCN occurs and a UCN disappears only by neutron β-decay.

View all citing articles on Scopus

¹: Mailing address: Hahn - Meitner Institut, D-1000 Berlin 39, Germany.

View full text

Article preview

Physics Letters A

Abstract

References (14)

Phys. Lett. A

Phys. Lett. A

Nucl. Instrum. Methods

Phys. Lett. A

Phys. Lett. A

Cryogenics

Phys. Lett. A

Cited by (41)

Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT

Neutron multigroup cross-sections of moderator materials for cold and ultracold neutron production

Experimental measurement of ultracold neutron production in superfluid <sup>4</sup>He

Production of UCN by downscattering in superfluid He<sup>4</sup>

Neutronic study of UCN production and storage in a liquid <sup>4</sup>He source

Quantitative evaluation of ultracold neutron production and storage in superfluid helium