Determination of the phonon spectrum from coherent neutron scattering by polycrystals

Breuer, N.

doi:10.1007/bf01677937

Cited by 8 publications

(4 citation statements)

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“…Although the higher mass of the deuteron and its stronger coherent scattering character with respect to the incoherent one limit the effectiveness of the incoherent approximation, a reliable DOPS extraction is still possible when a polycrystalline sample is considered . As also observed in the ice Ih case, the overall shape of both translational and librational bands are quite similar, and the small discrepancies between D 2 O and H 2 O are ascribable to the different coherent and incoherent scattering lengths of the two isotopes.…”

Section: Results and Discussionmentioning

confidence: 85%

Density of Phonon States in Cubic Ice Ic

et al. 2021

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Despite the simplicity of water molecules, for more than a century, a lot of scientific effort has been made on exploring ice polymorphism, especially more elusive phases such as cubic ice Ic. In this work, measurement of the density of phonon states (DOPSs) of polycrystalline ice Ic, and of its deuterated counterpart, has been performed in a sample having an almost perfect crystallographic purity, obtained from the transformation of ice XVII, and with a remarkable accuracy. Results are compared with the new accurate measurements of DOPSs in ice Ih and with centroid molecular dynamics (CMD) simulations. The differences between the experimental DOPSs in these two forms of ice are subtle but quantitatively measurable. In addition, they are reproduced semiquantitatively by computational methods, demonstrating the effectiveness of this innovative simulation tool for calculating the dynamical properties of ice structures.

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Section: Results and Discussionmentioning

confidence: 85%

Density of Phonon States in Cubic Ice Ic

et al. 2021

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“…The coherent (incoherent) neutron scattering cross sections for H, D and N atoms are 1.76 b (80.26 b), 5.59 b (2.05 b) and 11.01 b (0.50 b), respectively. For accurate determinations of the phonon density of states when the scattering is predominantly coherent, as in the case of ND 3 , it is very important to average the measured neutron scattering over a large volume of reciprocal space for the resulting data to reflect the true phonon density of states 29 . In the current experiment the ratio of the momentum transfer coverage to the Brillouin zone volume was about 20 for the lowest incident energy of 30 meV (and this value is larger for larger incident energy), therefore the condition of averaging was valid in the whole range of energy transfer studied.…”

Section: Resultsmentioning

confidence: 99%

Neutron scattering and neural-network quantum molecular dynamics investigation of the vibrations of ammonia along the solid-to-liquid transition

Linker,

Krishnamoorthy,

Daemen

et al. 2024

Nat Commun

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Vibrational spectroscopy allows us to understand complex physical and chemical interactions of molecular crystals and liquids such as ammonia, which has recently emerged as a strong hydrogen fuel candidate to support a sustainable society. We report inelastic neutron scattering measurement of vibrational properties of ammonia along the solid-to-liquid phase transition with high enough resolution for direct comparisons to ab-initio simulations. Theoretical analysis reveals the essential role of nuclear quantum effects (NQEs) for correctly describing the intermolecular spectrum as well as high energy intramolecular N-H stretching modes. This is achieved by training neural network models using ab-initio path-integral molecular dynamics (PIMD) simulations, thereby encompassing large spatiotemporal trajectories required to resolve low energy dynamics while retaining NQEs. Our results not only establish the role of NQEs in ammonia but also provide general computational frameworks to study complex molecular systems with NQEs.

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“…The GDOS(E ) provides an estimate of the excitation spectra in the sample [23]. First values of the generalized density of states (T 4 K and 23 K) were published by [20] and [24].…”

Section: ) Magnonmentioning

confidence: 99%

“…The term Q(< 2θ >) is a Q value for each energy transfer E considering an averaged scattering angle < 2θ >, while n is the Bose distribution for the phonons. Although oxygen is a purely coherent scatterer, it can be useful to use this approximation to obtain an estimate of the excitation spectra in the sample [20]. First results of the generalized density of states (T≃4 K and 23 K) were published by de Bernabe et al [21] and Kilburn et al [22].…”

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confidence: 99%

Production of ultra-cold neutrons in solid α-oxygen

Gutsmiedl

Böhle²,

Frei³

et al. 2011

EPL

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Our recent neutron scattering measurements of phonons and magnons in solid α-oxygen have led us to a new understanding of the production mechanism of ultra-cold-neutrons (UCN) in this super-thermal converter. The UCN production in solid α-oxygen is dominated by the excitation of phonons. The contribution of magnons to UCN production becomes only slightly important above E >10 meV and at E ∼4 meV. Solid α-oxygen is in comparison to solid deuterium less efficient in the down-scattering of thermal or cold neutrons into the UCN energy regime.PACS numbers: 28.20.Cz, 63.20.kk Ultra-cold-neutrons (UCN) are slow enough (∼ 300 neV) to be confined [1] in traps, which can be formed by materials with a high Fermi potential or by a magnetic field (60 neV/T). They can be kept for several minutes in the confinement, and thus be investigated with high precision. UCN are elementary particles that are extremely well suited for low-energy physics experiments. These experiments are investigating fundamental problems unsolved within the framework of the Standard Model [2]. One major experiment is the search for a non-zero electric dipole moment of the neutron [3] (current upper limit 2.9 10 −26 e· cm). Another unique experiment is the precise determination of the lifetime [4] of the free neutron. This value has an important impact on the theory of weak interaction [5].

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Determination of the phonon spectrum from coherent neutron scattering by polycrystals

Cited by 8 publications

References 0 publications

Density of Phonon States in Cubic Ice Ic

Density of Phonon States in Cubic Ice Ic

Neutron scattering and neural-network quantum molecular dynamics investigation of the vibrations of ammonia along the solid-to-liquid transition

Production of ultra-cold neutrons in solid α-oxygen

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