Every instrument at ISIS is a variation on one move — throw probes at a sample and study what comes out — but each technique asks a different question. Five you can play with below, one drawn out, three more in brief.
Two words to keep apart: a technique is the measurement move; a science group is the ISIS staff team and instrument suite that owns and runs it. ISIS organises its ~30 instruments into ten science groups, mostly one per technique family — each card below names its owner. The other two groups build the machine itself rather than run a technique: instrument Development (NMIDG) and Neutronics, who simulate neutron transport for targets and shielding.
The nine techniques
Technique 1 — neutron diffraction (powder)
Powder diffraction
“What crystal structure is this — and is it stressed, strained, or rearranging into a new crystal structure (a phase change)?”
Neutrons travel as waves, and waves reflecting off evenly spaced sheets of atoms reinforce each other only at special angles — that rule is Bragg’s law. So millions of randomly-oriented crystal grains diffract the beam at angles set by their atomic spacings, giving a fingerprint of peaks — move an atom, the fingerprint moves. The instrument converts angle and arrival time into d, the distance between atomic planes (in ångströms: 1 Å = 0.1 nm, about one atom’s width) — that’s the axis below. Try squeezing the lattice — the repeating grid the atoms sit on; a is its repeat distance:
on instruments like WISH · GEM · POLARIS · ENGIN-X (engineering strain)
science group: Crystallography (strain work on ENGIN-X: Engineering & Imaging)
“Where exactly is every atom — including the hydrogens?”
One perfect crystal diffracts into sharp spots. ISIS’s beam carries every wavelength at once, so even a stationary crystal lights up many spots per pulse — each spot picks out the wavelength that fits Bragg’s law for its own family of atomic planes. Map enough spots and you can place every atom in 3D. Rotate to bring new families into reach — then see what a powder “is”:
on instruments like SXD · WISH
science group: Crystallography
Technique 3 — small-angle neutron scattering
SANS
“How big are the particles, pores or droplets in here — and what shape?”
Big objects (1–100s of nm: polymers, proteins, precipitates) scatter at small angles. Q is a single number for how hard a neutron was deflected — a gentle nudge (small Q) means it bounced off something big, a sharp kick (large Q) means something small. The intensity curve I(Q) encodes size and shape — bigger particles push the pattern to smaller Q. Resize the spheres:
on instruments like SANS2D · LOQ · ZOOM
science group: SANS
Technique 4 — reflectometry
Neutron reflectometry
“How thick are these layers, and what’s buried at the interfaces?”
Skim the beam off a flat film and the reflectivity ripples — waves bouncing off the top and bottom of each layer interfere, adding up or cancelling depending on whether they arrive in step. Fringe spacing reads out layer thickness: thicker film, tighter fringes. Used on coatings, membranes, magnetic multilayers:
on instruments like INTER · POLREF · OFFSPEC
science group: Neutron Reflectometry
Technique 5 — neutron spectroscopy
Inelastic spectroscopy
“How do the atoms move — vibrations, rotations, magnetic waves?”
Diffraction asks where atoms are; spectroscopy asks what they’re doing. A neutron can give energy to the sample (excite a vibration) or steal some — that’s the “inelastic” part; an elastic bounce would keep it. Measure the energy change and you’ve recorded the material’s dynamics: how it conducts heat, stores hydrogen, or hosts exotic magnetism.
on instruments like LET · MAPS · MARI · MERLIN · TOSCA
“What’s the magnetic field like inside — atom by atom, even when it’s faint?”
A muon is a tiny spinning bar magnet. Park one in the sample and the local magnetic field makes its spin swivel like a wobbling top; when the muon dies (after ~2.2 µs on average) it fires out a positron roughly along its spin — so counting positrons replays the wobble. The wiggle frequency reads the field (in gauss — Earth’s is ≈ 0.5 G); how fast the wiggle dies reads the field’s disorder, λ. The plotted “asymmetry” is just positron counts in front minus behind. Turn the knobs:
X-ray-style radiography and CT-scan-style 3D tomography, but with neutron superpowers — neutrons light up hydrogen-rich stuff and sail through metal, the opposite of X-rays: see water in a running fuel cell, oil in an engine, or inside a fossil, without harm. IMAT · science group: Engineering & Imaging
Technique 8
Irradiation testing
Cosmic-ray neutrons randomly flip bits in electronics at altitude and on the ground. ChipIr replays years of that exposure in hours, so chips for aircraft, cars and data centres can prove they fail safely. ChipIr · science group: Engineering & Imaging
Technique 9
Total scattering & elemental analysis
Total scattering reads the local structure of glasses and liquids, where there’s no neat crystal. And a captured negative muon falls into an atom like a heavy stand-in electron, emitting element-specific X-rays as it settles — a fingerprint that identifies elements deep inside an object, gentle enough for Roman coins and meteorites. GEM · POLARIS (PDF — pair distribution function) · negative muons · science group: Disordered Materials (elemental analysis: Muon)
Schematic curves throughout — real data has resolution effects and backgrounds these toys skip. Simplified — the single-crystal animation draws the one-wavelength rotating-crystal picture; the real white beam lights many spots from a stationary crystal in every pulse. The real technique pages: isis.stfc.ac.uk/techniques.