Neutron_diffraction - Wikiparency

# Neutron diffraction ## Microsim (three.js) <div class="microsim-player">  <p class="wt-pending"><strong>Microsim staged, not yet on the CDN.</strong> <code>Neutron_diffraction.html</code> is built and deploy-ready in <code>Microsims for Dissemination/</code>, but the Netlify project still serves the geometry+spintronics set only. The player is disabled until the deploy lands; the explanatory text below is unchanged.</p>   </div> *In the REACTION chemistry hub, neutron diffraction turns a reactor's neutrons into a measuring stick: fission neutrons from [[Nuclear_fuel|nuclear fuel]], moderated to thermal energies, carry ångström-scale wavelengths that read out [[Crystal_structure|crystal structure]] much as X-rays do — except neutrons scatter from atomic nuclei and magnetic moments, not electron clouds.* > Neutron diffraction locates atoms inside a crystal by firing a neutron beam at it and recording which directions scatter strongly. Because a neutron's de Broglie wavelength is close to the spacing between atomic planes, the neutrons interfere like waves, producing sharp peaks wherever Bragg's law is satisfied. This microsim lets you steer that law by hand: set the wavelength, the plane spacing, and the glancing angle, then watch the reflected waves fall in or out of step. Stack more coherent planes and the peak sharpens; step the order and it jumps to a new angle — the same geometry real instruments use to map atomic and magnetic structure. ## About this microsim The sketch draws a stack of parallel lattice planes with an incoming neutron wave and its reflections, highlighting the extra path each deeper ray travels. Drag **Wavelength λ** (0.5–3.0 Å), **plane spacing d** (1.0–3.0 Å), and **glancing angle θ** (3–85°) to find the geometry where reflections from successive planes arrive in phase; the sim flags the moment nλ = 2d sinθ is met. The **diffraction order n** steps between successive Bragg reflections, while **coherent planes N** (2–10) sets how many planes scatter together — raise N and the peak snaps taller and narrower, exactly the way finite crystallite size controls peak width in a real diffractometer. ## Related microsims - X-ray — obeys the same Bragg law but scatters from electrons, so heavy atoms dominate and light ones hide - Electron diffraction — the third diffraction probe; a far stronger interaction suited to thin films and surfaces - [[Crystal_structure]] — what a full set of diffraction peaks is decoded back into - Thermal neutron — the ~25 meV, ~1.8 Å probe this technique depends on - [[Cubic_crystal_system]] — the simplest lattice whose plane spacings d feed straight into Bragg's law - [[Quasicrystal]] — sharp diffraction peaks from a structure that never repeats ## Links (Wikipedia order)  `Abnormal_grain_growth` · `Aerospace` · [[Alloy]] · `American_Crystallographic_Association` · 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`Vacancy_defect` · [[Vanadium]] · [[Velocity]] · `Wavelength` · [[Wayback_Machine]] · `Wigner_effect` · `William_Draper_Harkins` · `X-10_Graphite_Reactor` · `X-ray` · `X-ray_crystallography` · `X-ray_diffraction` · `Zeitschrift_für_Kristallographie_–_Crystalline_Materials` · `Zeitschrift_für_Kristallographie_–_New_Crystal_Structures` ## Overview Neutron diffraction is an elastic-scattering technique for determining the atomic and magnetic structure of solids and liquids. Ernest Wollan and Clifford Shull developed it at Oak Ridge National Laboratory in the 1940s using reactor neutrons; Shull shared the 1994 Nobel Prize in Physics for the method. Neutrons scatter from atomic nuclei rather than electrons, so their scattering strength varies erratically across the periodic table and even between isotopes. This makes light atoms such as hydrogen visible, distinguishes neighbouring elements, and enables isotopic contrast (hydrogen versus deuterium). Crucially, the neutron also carries a magnetic moment, so it scatters from ordered electron spins — the property Shull used for the first direct confirmation of antiferromagnetism, in MnO in 1949. Neutrons for such experiments come from research reactors and pulsed spallation sources. ## The physics A neutron of kinetic energy E has a de Broglie wavelength λ = h/√(2mₙE), where mₙ is the neutron mass and h is the Planck constant. Thermal neutrons in equilibrium near room temperature carry about 25 meV, giving λ ≈ 1.8 Å — comparable to interplanar spacings, which is what makes diffraction possible. The sim's wavelength range brackets this thermal value: | Neutron class | Energy E | Wavelength λ = h/√(2mₙE) | |---|---|---| | Hot | ≈ 325 meV | 0.5 Å (sim minimum) | | Thermal | ≈ 25 meV | 1.8 Å | | Cold | ≈ 9 meV | 3.0 Å (sim maximum) | Rays reflecting from adjacent planes separated by d differ in path length by 2d sinθ. They add constructively when that difference is a whole number of wavelengths — Bragg's law: nλ = 2d sinθ With N planes contributing coherently, the scattered intensity follows the N-slit interference function I ∝ [sin(Nφ/2)/sin(φ/2)]², where φ = (2π/λ)·2d sinθ. At the Bragg condition the peak height grows as N² and its angular width narrows as 1/N — the finite-size effect behind Scherrer crystallite-size broadening. ## Controls → what each maps to | Control | Maps to | Range / values | Physical meaning | |---|---|---|---| | Wavelength | λ | 0.5–3.0 Å | de Broglie wavelength of the neutron beam; thermal neutrons sit near 1.8 Å | | Plane spacing | d | 1.0–3.0 Å | perpendicular distance between adjacent lattice planes, fixed by the crystal and its Miller indices | | Glancing angle | θ | 3–85° | angle between the incident beam and the planes; the beam deflects by 2θ | | Coherent planes | N | 2–10 | number of planes scattering in phase; sets peak height (∝ N²) and width (∝ 1/N) | | Diffraction order | n | integer (Bragg nλ = 2d sinθ) | which Bragg reflection; higher n requires larger θ for fixed λ and d | ## Learning objective After playing, a learner can predict how the neutron wavelength, plane spacing, or glancing angle moves a Bragg peak, and explain why more coherent planes make it both sharper and brighter. ## Limits and connections This is a one-dimensional interference model: it captures Bragg geometry and finite-crystal peak shape, but not structure factors, the contrast between nuclear and magnetic scattering, absorption, or the broad Maxwellian spectrum of a real source (narrowed by a monochromator crystal or resolved by time-of-flight). The same nλ = 2d sinθ governs its sister probes below. ## Poster & source <div class="microsim-fallback">  <p><em>Live microsim · <a href="https://wikitube-3d-microsims.netlify.app/Neutron_diffraction.html">open full</a> · source: Microsims for Dissemination/REACTION/Neutron_diffraction.html</em></p> </div>  *Built to the [[WT!Three_js_Microsim_Master_Class|three.js Master Class]].*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Neutron_diffraction) : [Wikitube](https://en.wikitube.io/wiki/Neutron_diffraction) ## Previous hub tags Tree parent: [[Hydrogen]]. Legacy hubs: `REACTION`. --- *Sources: 1 legacy note. Minted wave 1, 2026-07-30 (v1.6 order).*