How ISIS works
Everything at ISIS exists to do one thing 50 times a second: make a pulse of protons, smash it into tungsten, and serve the debris — neutrons chipped from the tungsten, muons (the electron’s heavier, short-lived cousin) peeled off at a thin graphite slice on the way — to thirty-plus instruments. Four pulses in five go to Target Station 1; every fifth is kicked aside to Target Station 2, so the two halls run at 40 and 10 pulses a second. Click around the machine below.
Explore the facility
Pick a component
Click any highlighted part of the machine — or press Tab and Enter — to see what it does.
▶ ENTER TARGET STATION 1 — LIVE HALL VIEW
A working plan view of the TS1 hall: pulses landing, muons peeling off, and all eighteen beamlines drinking at once. Target Station 2 has its own tab.
Two ways to make neutrons
Reactor (e.g. ILL, Grenoble)
Nuclear fission gives a steady, continuous firehose of neutrons. Great brightness — but all wavelengths stream out jumbled together with no time structure, so you can’t sort them by arrival time: you select one narrow band and throw the rest away.
Spallation (ISIS, SNS, ESS)
Proton pulses chip neutrons off heavy nuclei in sharp bursts — to “spall” is to chip flakes off a rock. Quantum mechanics gives every moving particle a wavelength — the slower the neutron, the longer its wave — and every neutron in a burst starts its stopwatch together, so time-of-flight sorts them by wavelength and none are wasted. Less heat per neutron, too — and cooling the target is what ultimately caps a source’s brightness.
Moderators tune the wavelength menu
A moderator is a small tank of fluid that fresh neutrons pass through on their way out of the target. Inside, neutrons ricochet off the molecules until they move no faster than the molecules themselves — so the tank’s temperature decides how slow, and how long-wavelength, the neutrons come out. ISIS runs several around each target — TS1’s menu:
water ≈ 300 K (room temperature) → short wavelengths, for tightly-spaced atoms in metals and crystals.
liquid methane ≈ 100 K → mid-range.
liquid hydrogen ≈ 20 K (−253 °C) → long wavelengths, for big structures: polymers, proteins, membranes.
Each instrument looks at the moderator whose “menu” suits its science. TS2 was designed especially around cold, long-wavelength beams — its own pair is liquid hydrogen plus solid methane.
peak ≈ 1.1 Å — atomic-spacing territory