A differential time-of-flight spectrometer of very slow neutrons

Pokotilovski, Yu. N.; Novopoltsev, M. I.; Geltenbort, P.; Brenner, T.

doi:10.1134/s0020441210061077

Cited by 4 publications

(5 citation statements)

References 24 publications

(14 reference statements)

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“…From these data the UCN upscattering cross section on hydrogen, taken as the difference between the measured total scattering cross section σ n and the known (90 b) elastic σ el cross section, is σ up (4 m/s) = 1972 ± 130 b. Our measurements support recent TOF measurements of Pokotilovski et al [13], but disagree with the measurements of Zhukov et al [12], which served the UCN community for a long time as the only experimental data on upscattering in CH 2 . It should be noted that our mcnp calculations [8] of σ up for CH 2 agree with [12] in disagreement with our experimental result.…”

supporting

confidence: 86%

“…Lower upscattering cross sections values for hydrogen in polyethylene have been obtained from the recent UCN time-of-flight measurements [13], where the σ up (E) was shown to follow the 1/v law with the value σ up (4 m/s) = 2053 ± 40 b, at 4 m/s . The reasons for the disagreement between the results of measurements [12] and [13] remain unclear.…”

mentioning

confidence: 95%

“…For hydrogen the relationship between absorption and upscattering is reversed: the average UCN upscattering cross section, according to the measurement [12], is 3745 ± 370 b while the thermal cross section value σ a = 0.3326 ± 0.0007 [10] and the 1/v law leads to σ a (4 m/s) = 182.9 b. Lower upscattering cross sections values for hydrogen in polyethylene have been obtained from the recent UCN time-of-flight measurements [13], where the σ up (E) was shown to follow the 1/v law with the value σ up (4 m/s) = 2053 ± 40 b, at 4 m/s . The reasons for the disagreement between the results of measurements [12] and [13] remain unclear.…”

mentioning

confidence: 99%

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Measurements of ultracold neutron upscattering and absorption in polyethylene and vanadium

Sharapov¹,

Morris²,

Makela³

et al. 2013

Phys. Rev. C

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The study of neutron cross sections for elements used as efficient "absorbers" of ultracold neutrons (UCN) is crucial for many precision experiments in nuclear and particle physics, cosmology and gravity. In this context, "absorption" includes both the capture and upscattering of neutrons to the energies above the UCN energy region. The available data, especially for hydrogen, do not agree between themselves or with the theory. In this report we describe measurements performed at the Los Alamos National Laboratory UCN facility of the UCN upscattering cross sections for vanadium and for hydrogen in CH2 using simultaneous measurements of the radiative capture cross sections for these elements. We measured σup = 1972±130 b for hydrogen in CH2, which is below theoretical expectations, and σup < 25 ± 9 b for vanadium, in agreement with the expectation for the neutron heating by thermal excitations in solids. PACS numbers: 25.40.Fq, 25.40.Kv, 28.20.Ka Several recent reviews highlight the application of ultracold neutrons in past and ongoing experiments for searching for the neutron electric dipole moment [1], for precision measurement of the neutron lifetime [2], for neutron β-decay correlations [3] and for gravitational quantum states [4], as well as for solving new issues in cosmology [5]. Ultracold neutrons greatly increase the sensitivity of experiments because they can be confined in the apparatus for times comparable with the neutron lifetime owing to the action of the 'optical' Fermi potential, U F ,where m is the neutron mass, N is the number density of the material, and b is the neutron scattering length. Materials with high positive potential, U F 250 neV, are used for trapping UCN because neutrons with kinetic energy lower than that value are reflected from walls at all angles of incidence. The velocity of such neutrons is below 7 m/s. On the other hand, materials made from elements with a small negative optical potential, like hydrogen, vanadium, titanium serve for removal of UCN through absorption and/or upscattering to higher energy. The efficiency of this removal is important for many measurements and this continues to motivate the study of such materials. Vanadium and hydrogen are perfect neutron incoherent scatterers, and both have small negative, practically non-reflective potential U F −7.1 neV. For these elements, the theory of upscattering in one-phonon incoherent approximation is usually applied in the theory of upscattering, and the UCN isotropic differential upscattering cross section for cubic lattices can be calculated by a simple formula [6]:where σ b = 4πb 2 is the cross section for bound nuclei with the mass number A, E i is the initial UCN energy, E is the energy after upscattering, g(E) is the phonon density of states and the last exponent is the Debye-Waller factor * Corresponding author; Electronic address: morris@lanl.gov

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supporting

confidence: 86%

mentioning

confidence: 95%

mentioning

confidence: 99%

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Measurements of ultracold neutron upscattering and absorption in polyethylene and vanadium

Sharapov¹,

Morris²,

Makela³

et al. 2013

Phys. Rev. C

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“…Slow neutrons -especially ultracold neutrons (UCNs), with a velocity of only a few meters per second and a wavelength of several hundred Ångström -are, however, sensitive to surface roughness 1 , material 2,3 and magnetic inhomogeneities 4 . Besides that, aluminum windows are not optically transparent and thus do not allow for an online control of the sample.…”

Section: Introductionmentioning

confidence: 99%

A hydrogen leak-tight, transparent cryogenic sample container for ultracold-neutron transmission measurements

Döge

Hingerl

2018

Review of Scientific Instruments

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The improvement of the number of extractable ultracold neutrons (UCNs) from converters based on solid deuterium (sD) crystals requires a good understanding of the UCN transport and how the crystal's morphology influences its transparency to the UCNs. Measurements of the UCN transmission through cryogenic liquids and solids of interest, such as hydrogen (H) and deuterium (D), require sample containers with thin, highly polished and optically transparent windows and a well defined sample thickness. One of the most difficult sealing problems is that of light gases like hydrogen and helium at low temperatures against high vacuum. Here we report on the design of a sample container with two 1 mm thin amorphous silica windows cold-welded to aluminum clamps using indium wire gaskets, in order to form a simple, reusable, and hydrogen-tight cryogenic seal. The container meets the above-mentioned requirements and withstands up to 2 bar hydrogen gas pressure against isolation vacuum in the range of 10 to 10 mbar at temperatures down to 4.5 K. Additionally, photographs of the crystallization process are shown and discussed.

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“…Hydrogen has one of the largest inelastic scattering cross section of all elements. It is most convenient to study it in polyethylene, [C 2 H 4 ] n , in which the hydrogen inelastic cross section increases as the inverse velocity law to the value of 2053±40 barn [6] at a velocity of 4.0 m/s. Authors of Refs.…”

mentioning

confidence: 99%

Upscattering of ultracold neutrons from the polymer [C6H12]n

Sharapov¹,

Morris²,

Makela³

et al. 2013

Phys. Rev. C

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It is generally accepted that the main cause of ultracold neutron (UCN) losses in storage traps is upscattering to the thermal energy range by hydrogen adsorbed on the surface of the trap walls. However, the data on which this conclusion is based are poor and contradictory. Here we report a measurement, performed at the Los Alamos National Laboratory UCN source, of the average energy of the flux of upscattered neutrons after the interaction of UCN with hydrogen bound in the semicrystalline polymer PMP (trade name TPX), [C 6 H 12 ] n . Our analysis, performed with the MCNP code which applies the neutron-scattering law to UCN upscattered by bound hydrogen in semicrystalline polyethylene, [C 2 H 4 ] n , leads us to a flux average energy value of 26 ± 3 meV, in contradiction to previously reported experimental values of 10 to 13 meV and in agreement with the theoretical models of neutron heating implemented in MCNP.

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A differential time-of-flight spectrometer of very slow neutrons

Cited by 4 publications

References 24 publications

Measurements of ultracold neutron upscattering and absorption in polyethylene and vanadium

Measurements of ultracold neutron upscattering and absorption in polyethylene and vanadium

A hydrogen leak-tight, transparent cryogenic sample container for ultracold-neutron transmission measurements

Upscattering of ultracold neutrons from the polymer [C6H12]n

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