Ultra cold neutron production by multiphonon processes in superfluid helium under pressure

Schmidt-Wellenburg, P.; Andersen, K.H.; Zimmer, O.

doi:10.1016/j.nima.2009.07.085

Cited by 24 publications

(35 citation statements)

References 24 publications

(39 reference statements)

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“…The single-phonon UCN production peak moves to a shorter wavelength and decreases in intensity, whereas the absolute contribution from multiphonon processes stays constant within the experimental uncertainties. We have found that predictions from calculations based on inelastic neutron scattering data [32,33] agree well with the behavior of the single-phonon UCN production rate. However, the same calculations disagree with our measurement in the multiphonon range.…”

Section: Discussionmentioning

confidence: 60%

“…This behavior can be well understood by taking a , and UCN production rates compared with results given in Refs. [32,33] calculated from scattering data. UCN production rates are normalized to the incident cold neutron flux.…”

Section: Discussionmentioning

confidence: 99%

“…The calculations in Refs. [32,33] employ scattering data measured at 0.5 K, whereas our measurements were done at 1.1 K. An increasing temperature results, for example, in a broadening of the single-phonon excitation. This increase is small at low temperatures but becomes large towards the λ transition [30].…”

Section: Discussionmentioning

confidence: 99%

“…In Ref. [30] the temperature dependence of the single-phonon excitation linewidth for different pressures was determined from fits to the measured [32,33]. Both dependencies have been normalized to the respective production rate at SVP.…”

Section: Discussionmentioning

confidence: 99%

“…Using the entire spectrum of a white beam might still be advantageous for a powerful UCN source, as monochromatization by a crystal not only cuts out a narrow wavelength band around 8.92Å but also reduces the intensity of the Bragg reflected beam substantially (by a factor of 2-5 [20,32]). In either case, monochromatic or white incident beam, the best results are obtained for He-II at SVP, without even taking into account the increase in technical complexity when going to higher pressures.…”

Section: Discussionmentioning

confidence: 99%

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Experimental study of ultracold neutron production in pressurized superfluid helium

et al. 2015

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We investigate experimentally the pressure dependence of the production of ultracold neutrons (UCNs) in superfluid helium in the range from saturated vapor pressure to 20 bar. A neutron velocity selector allows the separation of underlying single-phonon and multiphonon processes by varying the incident cold neutron (CN) wavelength in the range from 3.5 to 10Å. The predicted pressure dependence of UCN production derived from inelastic neutron scattering data is confirmed for the single-phonon excitation. For multiphonon-based UCN production we found no significant dependence on pressure, whereas calculations from inelastic neutron scattering data predict an increase of 43(6)% at 20 bar relative to saturated vapor pressure. From our data we conclude that applying pressure to superfluid helium does not increase the overall UCN production rate at a typical CN guide.

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Section: Discussionmentioning

confidence: 60%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Experimental study of ultracold neutron production in pressurized superfluid helium

et al. 2015

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Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT

Schmidt-Wellenburg

Andersen

Courtois

et al. 2009

Nuclear Instruments and Methods in Physics Research Section A:

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UCN sources at external beams of thermal neutrons. An example of PIK reactor

Лычагин

Mityukhlyaev

Muzychka

et al. 2016

Nuclear Instruments and Methods in Physics Research Section A:

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. AbstractWe consider ultracold neutron (UCN) sources based on a new method of UCN production in superfluid helium ( 4 He). The PIK reactor is chosen as a perspective example of the application of this idea, which consists of installing a 4 He UCN source in a beam of thermal or cold neutrons and surrounding the source with a moderator-reflector, which plays the role of a source of cold neutrons (CNs) feeding the UCN source. The CN flux in the source can be several times larger than the incident flux, due to multiple neutron reflections from the moderator-reflector. We show that such a source at the PIK reactor would provide an order of magnitude larger density and production rate than an analogous source at the ILL reactor.We estimate parameters of a 4 He source with solid methane (CH4) or/and liquid deuterium (D2) moderator-reflector. We show that such a source with CH4 moderator-reflector at the PIK reactor would provide the UCN density of ~110 5 cm -3 , and the UCN production rate of ~210 7 s -1 . These values are respectively 1000 and 20 times larger than those for the most intense UCN user source. The UCN density in a source with D2 moderator-reflector would reach the value of ~210 5 cm -3 , and the UCN production rate would be equal ~810 7 s -1. Installation of such sources in beams of CNs with equal flux would slightly increase the density and production rate. IntroductionA new concept of super-thermal liquid-helium ( 4 He) UCN sources is presented in ref.[1]. Such sources can be installed in beams of thermal neutrons; thus at ILL (Grenoble) or PIK (Gatchina) such a source would provide parameters highly exceeding those of existing UCN sources. The present work develops ref.[1], considers source parameters in more detail, and applies the new concept to the PIK reactor. Note, however, that such a UCN source can be installed at any other thermal neutron source as well.The idea of 4 He UCN sources was proposed in 1975 in ref.[2]; it is based on neutron scattering in liquid 4 He accompanied with exciting phonons with the energy of 1.02 meV. If the incident neutron energy is slightly higher than 1.02 meV then the cold neutron (CN) is converted into a UCN. As the UCN energy is lower than ~300 neV, only CNs from a very narrow energy range contribute to the UCN production. Cross-sections of simultaneously exciting two or more phonons are lower by a few orders of magnitude. However, the energy of excited phonons is found in a broad range, thus UCNs are produced via multi-phonon processes from a broad spectrum of incident neutrons. Therefore total contributions of one-phonon and multi-phonon process are comparable if the incident neutron spectrum is broad.Work [2] showed also that produced UCNs can live for a long time in superfluid 4 He if its temperature is below 1K. Long lifetimes of UCNs allow accumulating them up to high densities. Neutron storage time changes sharply as a function of helium temperature. It equals to the neutron lifetime ~880 s at the temperature of 0.8 K, it is 10 times longer than that a...

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Ultra cold neutron production by multiphonon processes in superfluid helium under pressure

Cited by 24 publications

References 24 publications

Experimental study of ultracold neutron production in pressurized superfluid helium

Experimental study of ultracold neutron production in pressurized superfluid helium

Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT

UCN sources at external beams of thermal neutrons. An example of PIK reactor

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