Backstage Science: Engin-X

Ania Paradowska and Joe Kelleher explore the Engin-X beam line, explaining how it works and its many uses.

Engin- X is a ‘beam line’ at the huge ISIS research centre.

It probes samples with a stream of neutrons from the main source

But Engin-X is a bit different from other instruments

Ania Paradowska: “Neutrons are coming from this building and they are going through this brown guide to the hatch”

Joe Kelleher:    “The neutron has come down from the source inside the guide. Inside the guide are surfaces of mirrors, so if the neutron tries to stray out it bounces back. Some neutrons are travelling faster, some are travelling slower. Eventually, emerging through this hole, it passes through a series of slits that chops down the beam, of which our neutron is just one part, eventually passing into the sample. There are countless number of atoms in the sample, of which it will probably strike one of them and when it does, it can move in any direction. Hopefully, it will pass into one of these detectors. The neutrons will travel straight and eventually, it is detected by a series of scintillators, which will glow briefly.

We know the time it arrives, we know the wavelengths, we know the spacing between the atoms that the neutron has bounced off and ultimately we can tell a lot about the material just from the positions of its atoms. That explains a lot about how the material behaves and how likely it is to become damaged in service”

Engin- X specialises in analysis of engineering samples. Sometimes they're very big.

 Ania Paradowska: “We do lots of typical engineering components. But we occasionally do quite interesting components like train wheels, which are for example 500 kg. Other interesting components include an airbus wing.

Joe Kelleher:   “We measure real samples that actually serve a purpose, like in aeroplanes, automobiles, trains. 

We certainly have some very large samples in here. Luckily, we have a crane to get them in. Two tonnes or so this will take. We once had a massive block of magnesium that was actually cast from the factory and it turned out we saw absolutely nothing. It turned out they had small traces of gadolinium in the casting, which is about probably at least 100,000 times more absorbing than any other metal. We didn't know this was a problem at the time but it was very frustrating. We eventually made another one that didn't have gadolinium and it worked perfectly.

If you were down at the size of the atom, firstly you would see the atoms are quite nicely arranged, like oranges stacked on a supermarket shelf and it’s the fact that they're in this pattern that allows this type of experiment to be done. A single atom is too small for a technique like this to see, but the fact that they're arranged in a regular spacing means that we can work out the average gap between a large number of atoms together.

Ania Paradowska: “I find this very interesting because it is one of the best instruments in the world and it is extremely powerful. Having 2400 detectors on each side at 90 degrees and a hundred detectors on the transmission detector, this is not a piece of kit you can have everyday to play with. I really feel quite lucky to be here”

Joe Kelleher:  “You re the size of an atom, you see a neutron come in and it will miss most of the atoms, it will bounce off one or two. Eventually enough neutrons are bounced off enough atoms for a pattern to form. The pattern that you form in the detectors is related to how the atoms are arranged”.

Ania Paradowska: “The possibility that we can help scientists from archaeologists to engineers, who are designing new bridges, cars and power stations is quite rewarding. In a way, I think that we can make a difference here”.

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