Backstage Science: How to make neutrons
18 Aug 2011



Martyn Bull gives us a tour of ISIS, showing us where the neutrons are made and how this happens




Neutrons can be used to study materials at the atomic level.

One of the best places for this kind of research is ISIS, in Oxfordshire, UK.

So how do they produce their neutrons?

Martyn Bull:  “The ISIS neutron source is one of the most famous research centres. You can see the flags of all of out partner countries. ISIS is situated around an accelerator, a synchrotron, which takes protons and accelerates them to a high speed. When they've reached their final speed, they're fired off down this beam line here, where they hit the target. The energy is dispersed by causing the atoms of the target to release neutrons, which then fly out in all directions down to the beam lines.

Every different beam line or neutron instrument is dedicated to doing a different type of science; it could be physics or chemistry. Some of them are looking at the structure of the materials and some of them are looking at the dynamics or the motions of the atoms.

This is the main control room where we run the accelerator from. We're going to see the experimental areas. Welcome to ISIS target station one, its pretty big. Down the middle is the proton beam, which is fired from the accelerator. Towards the far end of the hall is the bunker in which the neutron target lives. We re walking on top of the proton beam, so beneath our feet, bunches of proteins travelling at near the speed of light.

Over this balcony, you can see the targets. You can see different coloured areas which are for different experiments. The neutrons coming out are very fast and are at a too high speed to be useful for experiments, so we have to slow them down. They pass through little boxes of things like liquid hydrogen and liquid methane, called moderators. All that is contained inside the bunker because as well as neutrons coming off there’s all sorts of other things coming off like high energy gamma rays and things you don't want to come out into the experimental halls. So the shielding is about four metres thick and only the neutrons come out into the beam lines where we want them.

Every beam line has a name. Some places in the world choose to number their beam lines, but at ISIS they've all go names that you can remember. This one is called Crisp. Rumour has it that it was named after a famous race horse. We've got ones called Tosca, Merlin, just goes along with the imaginations of the scientific teams who've helped to build them.

The beam lines are switched off. Normally we would have to open all the keys and the gates but it’s open so we can just walk in. Behind this wall, some metres back, it’s the neutron target. It’s releasing neutrons when it’s operating. They come through this small hole, into the beam line and pass through all the various components, which are used to treat the beam and get it to have all the right qualities. It reaches the sample position, where you put the thing you want to measure. The beam then carries on through the other components until it reaches the detector, which will give a data pattern. The data pattern is related to the structure of the sample that is in the beam. Then you have to work backwards and figure out what happened to give you the pattern in the computer, so that you can understand what happened in the material. That’s the day to day life of an experiment.

Neutrons are a brilliant way to measure things. As a particle, they have no electrical charge, which means that when they pass through matter they don't cause any disruption like an x-ray would or even a proton would. They don't cause any physical damage. Because they have no electrical charge, they're also very penetrating, so you go beyond the surface and deep into the material and so get to see what is happening right inside. They also have a magnetic component to them, so they are able to measure magnetism.  They've go a set of qualities that gives them a completely unique view of the world.

We're going outside to the second target station, which is this big white building here.  We were given £145 million from the government to expand because we are so popular. We also wanted to do new science, which was difficult to fit into the old target station. We send four pulses in five to target station one and the fifth one goes to target station two.

This building is the size of a small football stadium. These are magnets from the proton beam, they're spares. These coils are where you put the electrical current that generates the magnetic fields. The beam of particles travels through the centre, usually in a tube, with all the air sucked out.

It seems pretty quiet in here at the moment and that’s because we're just getting ready to do experiments. This means we can go inside.  When we're running, we have about 800 experiments running each year, with over 2000 research visitors coming. The big blue bunker in the centre is where the target lives. This target station is tiny; it’s about the size of a packet of biscuits. This tiny object receives a high energy proton beam; 48kW of power is dumped into this. It liberates all its neutrons and we have to cool it with water to stop it melting. Some of the range of science that’s taken place on this target station over the last year includes surgeons from the John Radcliff’s hospital, looking at an implant that can be used to treat cleft palettes, right through to researches developing a new way to store hydrogen so that it can be used for  cars. A complete spread of science”.