Spinning electrons

I have now been in Grenoble in France for a couple of weeks, where I am doing a course on what experiments can be done with synchrotron x-rays and neutrons. Here in Grenoble, one of the most powerful synchrotrons in the world is situated, which I guess is the reason for the course taking place here. We are a group of 75 students on the course, most of us are PhD candidates, but there are also some senior scientists. The course is called HERCULES, and it has been on each year for 20 years now. That means that quite a bit of the research community working with synchrotron and neutron radiation has been through this course, and they have a pretty good line-up of lectureres.

Anyway, what's a synchrotron? Well, it's a big ring where electrons run around at a speed close to the speed of light. They are kept going around in the circle by magnetic fields that are guiding them around. When these electrons are pulled around by the magnetic field, they start emitting very high energetic radiation in the same direction as they are propagating. This radiation is mainly consisting of x-rays, which can be pretty useful for many things. The main thing about x-rays, as you probably know already, is that they go through things that normal light does not go through. They are also smaller (have shorter wavelength) than light, so they can see smaller things. And last but not least, if they propagate through a crystal, the atoms in the crystal can spread the x-rays into a special pattern that gives a lot of information about the crystallic structure. That's what's important to me, and many other researchers. A lot of things are crystalline, and certainly most semiconducturs, which is what we are making solar cells of. But you can discover crystalline structures even in chocolate, as some of the participants in the course have been able to see in their practicals.

Neutrons techniques is the other subject of the course. The neutrons can do similar things as the x-rays. Although neutrons constitute about half of the matter on earth, they are not so easy to get out from the atoms. You actually need a huge thing to kick the neutrons out, as for example a nuclear reactor. The fission of uranium gives neutrons flying out in every direction, which in energy reactors could be considered a problem. However, the neutrons has the property that they penetrate through things that not even x-rays would consider possible, so they can be quite
useful for structural analysis.

Here's a photo of the synchrotron ring and the reactor here in Grenoble, from a photo I took on my mountain hike this Saturday: