Enviar artigo por via de e-mail Time-of-flight neutron reflectometer for compact neutron source DARIA: Monte-Carlo simulations
- Autores: Grigoryeva N.А.1, Kovalenko N.А.2,3, Grigoriev S.V.2,3
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Afiliações:
- M.N. Mikheev Institute of Metal Physics, Ural Branch of Russian Academy of Sciences
- Saint Petersburg State University
- NRC “Kurchatov Institute”
- Edição: Nº 12 (2024)
- Páginas: 102-117
- Seção: Articles
- URL: https://journal-vniispk.ru/1028-0960/article/view/286151
- DOI: https://doi.org/10.31857/S1028096024120126
- EDN: https://elibrary.ru/QWHZQU
- ID: 286151
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Resumo
Two types of reflectometers have been simulated for the compact neutron source DARIA (Dedicated for Academical Research and Industrial Application), depending on the type of target assembly with thermal or cryogenic moderators. Modeling and optimization of reflectometers were carried out using McStas software package by Monte–Carlo method with given momentum transfer resolution Δq/q ≤ 5% for reflection angles greater than the θcr critical angle and horizontal divergence of the neutron beam of Δθ ≤ 0.1° for θ < θcr and Δθ ≤ 0.033° for θ > θcr. To reduce losses in neutrons, neutron guides with a supermirror coating have been proposed. A system of choppers makes it possible to create a neutron spectrum of the required width on a sample.
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Sobre autores
N. Grigoryeva
M.N. Mikheev Institute of Metal Physics, Ural Branch of Russian Academy of Sciences
Autor responsável pela correspondência
Email: n.a.grigorieva@yandex.ru
Rússia, Ekaterinburg
N. Kovalenko
Saint Petersburg State University; NRC “Kurchatov Institute”
Email: n.a.grigorieva@yandex.ru
Petersburg Nuclear Physics Institute named by B.P. Konstantino
Rússia, St. Petersburg; GatchinaS. Grigoriev
Saint Petersburg State University; NRC “Kurchatov Institute”
Email: n.a.grigorieva@yandex.ru
Petersburg Nuclear Physics Institute named by B.P. Konstantino
Rússia, St. Petersburg; GatchinaBibliografia
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Fig. 1. Neutron transmission coefficient through a beryllium filter (a) and the ratio of the time dependences of the intensity of the neutron beams passed through the beryllium filter and the original beam (b).
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Fig. 2. Time-distance diagram for the spectral range of neutron pulses from 1 to 10 Å (highlighted by curly brackets). Four pulse sequences are shown. The horizontal lines mark the positions of the chopper at L = 14 (3) and 8 m (3’) and the detector at L = 14 (7) and 8 m (7’). The periodicity of the neutron pulses corresponds to T = 1/fp.
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Fig. 3. Dependence of the relative resolution of the reflectometer for the transmitted momentum Δq/q on the neutron wavelength for grazing angles of 1.5 (1); 4.5 (2); 11.5 (3); 17.5 (4); 21 mrad (5).
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Fig. 4. Schematic diagram of a neutron reflectometer for a target with thermal and cryogenic moderators: 1 — neutron source; 2 — curved neutron guide; 3 — three-disk beam chopper; 4 — straight neutron guide; 5 — collimation slits; 6 — sample unit; 7 — two-coordinate position-sensitive detector; 8 — neutron beam polarizer; 9 — radio-frequency adiabatic device for neutron spin flip; 10 — fan multi-slit analyzer. The scale at the top indicates the distances from the moderator surface to the reflectometer units.
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Fig. 5. Spectral (top) and time (bottom) dependences of the intensity of the neutron pulse emitted from a cryogenic mesitylene moderator with a diameter of 0.1 m. The time-averaged neutron flux is Φ = 5.86 × 108 n⋅cm–2 ⋅ s–1 in the wavelength range from 0.5–10 Å.
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Fig. 6. At the top is the spectral dependence of the neutron momentum that passed through a curved neutron guide 4.8 m long, with a radius of curvature Rn = 1152 m and an internal cross-section of 0.01 × 0.05 m. The time-averaged neutron flux is Φ = 3.3 × 106 n⋅cm–2 ⋅ s–1 in the wavelength range from 0.5–10 Å. At the bottom is the neutron beam profile at the exit from the curved neutron guide.
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Fig. 7. Spectral dependence of the intensity of the neutron beam that passed through the first and second chopper disks for three wavelength ranges δλ. Empty circle — chopper 1: δλ = 1Å – – 7Å = 6 Å, filled circle — chopper 2: δλ = 1Å — 7Å = 6 Å, the time-averaged neutron flux is Φ = 1.35 × 106 n⋅cm–2 ⋅ s–1. The empty square is chopper 1: δλ = 4Å – 10Å = 6 Å, the filled square is chopper 2: δλ = 4Å –10 Å = = 6 Å, Φ = 9.0 × 105 n⋅cm–2 ⋅ s–1. The empty triangle is chopper 1: δλ = 2Å – 8 Å = 6 Å, the filled triangle is chopper 2: δλ = 2Å – 8 Å = 6 Å, Φ = 1.35 × 106 n⋅cm–2 ⋅ s–1.
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Fig. 8. Spectral dependences of the intensity of the neutron beam passed through the first (empty symbols) and third (solid symbols) chopper disks for the wavelength ranges δλ specified by the first chopper disk, from 1 to 7 Å (a) and from 3 to 9 Å (b). The third disk cuts out the spectral width of neutrons δλ = 3Å. (a) Empty circle — chopper 1: δλ = 1Å — 7Å = 6 Å, filled circle — chopper 3: δλ = 1Å — 4Å = 3 Å, the time-averaged neutron flux is Φ = 1.34 × 106 n⋅cm–2 ⋅ s–1; filled square — chopper 3: δλ = 2Å — 5Å = 3 Å, Φ = 1.74 × 106 n⋅cm–2 ⋅ s–1; filled triangle — chopper 3: δλ = 4Å — 7Å = = 3 Å, Φ = 1.24 × 106 n⋅cm–2 ⋅ s–1. (b) — empty circle — chopper 1: δλ = 3Å — 9Å = 6 Å, filled circle — chopper 3: δλ = 3Å — 6Å = 6 Å, Φ = 1.6 × 106 n⋅cm–2 ⋅ s–1; filled square — chopper 3: δλ = 5Å — 8Å = 3 Å, Φ = 8.84 × 105 n⋅cm–2 ⋅ s–1; filled triangle — chopper 3: δλ = 6Å — 9Å = 3 Å, Φ = 6.2 × 105 n⋅cm–2 ⋅ s–1.
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Fig. 9. Spectral dependences of the neutron beam intensity at the output of the straight neutron guide for the λ range from 1 to 7 Å (a) at a neutron guide cross section of 0.01 × 0.05 m (empty symbols), Φ = 9.45 × 105 n⋅cm–2 ⋅ s–1. and 0.005 × 0.05 m (solid symbols), Φ = 1.06 × 106 n⋅cm–2 ⋅ s–1. For the λ range from 4 to 10 Å (b) at a neutron guide cross section of 0.01 × 0.05 m (empty symbols), Φ = 5.5 × 105 n⋅cm–2 ⋅ s–1. and 0.005 × 0.05 m (solid symbols), Φ = 6.06 ×105 N⋅cm–2 ⋅ s–1.
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Fig. 10. Dependence of the neutron flux at the exit from the neutron guide (a): curved, with a cross-section of 0.01 × 0.05 m (solid symbols); straight, with a cross-section of 0.005 × 0.05 m (empty symbols); and after collimation slits of 0.001 × 0.05 m (b) on the parameter of the neutron guide supermirrors m.
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Fig. 11. Horizontal divergence of the neutron beam on a sample in a neutron reflectometer for a target with thermal and cryogenic moderators and a time-of-flight baseline of L = 14 m.
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Fig. 12. Spectral dependences of the momentum of neutrons incident on the sample for different configurations of chopper disks and λ ranges. Solid circles: disk 1 + disk 2, δλ = 6 Å (λ from 1 to 7 Å), the time-averaged neutron flux is Φ = 3.91 × 104 n⋅cm–2 ⋅ s–1; empty circles: disk 1 + disk 3, δλ = 3 Å (λ from 1 to 4 Å), Φ = 5.66 × 104 n⋅cm–2 ⋅ s–1; empty triangles — disk 1 + disk 3, δλ = 3 Å (λ from 4 to 7 Å), Φ = 2.02 × 104 n⋅cm–2 ⋅ s–1.
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Fig. 13. Schematic diagram of a neutron reflectometer for a target with a thermal moderator: 1 – neutron source; 3 – single-disk beam chopper; 4 – straight neutron guide; 5 – collimation slits; 6 – sample unit; 7 – two-coordinate position-sensitive detector; 8 – neutron beam polarizer; 9 – radio-frequency adiabatic device for neutron spin flip. The scale at the top indicates the distances from the moderator surface to the reflectometer units.
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Fig. 14. Spectral (top) and time (bottom) dependences of the momentum of neutrons emitted from a thermal (water) pre-moderator with a diameter of 0.1 m. The time-averaged neutron flux is Φ = 3.86 × 108 n⋅cm–2 ⋅ s–1 in the wavelength range from 0.5–10 Å.
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Fig. 15. Spectral dependence of the neutron momentum passed through a straight neutron guide 2.4 m long with an internal cross-section of 0.01×0.05 m. The time-averaged neutron flux is Φ = 1.34 × 106 n⋅cm–2 ⋅ s–1 in the wavelength range from 0.5–10 Å.
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Fig. 16. Dependence of the neutron flux at the exit from a straight neutron guide with a cross-section of 0.01 × 0.05 m (solid symbols) and after collimation slits with a size of 0.001 × 0.05 m (empty symbols) on the parameter of the neutron guide supermirrors m.
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Fig. 17. Spectral dependence of the intensity of the neutron beam passed through a single-disk chopper. The time-averaged neutron flux is Φ = 1.17 × 106 n⋅cm–2 ⋅ s–1 in the wavelength range from 0.5–10 Å.
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Fig. 18. Horizontal divergence of the neutron beam on a sample in a neutron reflectometer on a target with a thermal moderator and a time-of-flight baseline L = 8 m.
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Fig. 19. Comparison of spectral dependences of the neutron momentum (δλ = 6 Å) incident on the sample for reflectometers with a cryogenic moderator and L = 14 m (solid symbols), Φ = 3.91 × 104 n⋅cm–2 ⋅ s–1; with a thermal pre-moderator and L = 8 m (empty symbols), Φ = 5.13 × 104 n⋅cm–2 ⋅ s–1.
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