Happy 40th birthday, ILL

Behind the bike sheds: the view from ILL

By Hamish Johnston

Yesterday I made a flying visit to what is arguably the world’s most famous lab for neutron science – the Institut Laue-Langevin (ILL). Nestled between jagged mountains at the edge of the French Alps, the reactor at ILL has been reliably churning out neutrons since the reactor in Grenoble first went critical in 1971.

Like all neutron sources, the majority of the facility’s 40 or so instruments don’t study the neutron itself – but rather use beams of neutrons to work out the structure and composition of objects as varied as railway tracks and human proteins.

However, ILL is unique in that a significant chunk of the research that goes on there (about 15%) is devoted to the study of the neutron. To do this, ILL physicists make ultracold neutrons, or UCNs, which move so slowly that they would be overtaken in a race by a decent human sprinter.

The amazing thing is that UCNs can be collected and stored in containers like the one pictured on the right. There they can be observed for relatively long periods of time to see, for example, if they change (or oscillate) into antineutrons. Such an oscillation is forbidden by the Standard Model of particle physics and seeing it could point towards new physics.

In Grenoble I interviewed two leading UCN physicists, Peter Geltenbort and Oliver Zimmer, so stay tuned to physicsworld.com for much more about UCNs. I was also lucky enough to have a tour of the reactor and one of ILL’s experimental halls guided by Peter and Oliver. You can see the photos that I took over on our Flickr page.

This year is the 40th anniversary of ILL and I recorded an interview with the facility’s scientific director Andrew Harrison. As well as telling me about the four new instruments being built at ILL, Andrew looked to the future and shared his vision of how ILL will play a complementary role to the European Spallation Source due to be built in Sweden in 2025. Again, stay tuned to physicsworld.com for more from Andrew.