European Project Aims to Build World's Most Powerful Neutron Source

The European Spallation Source will have gigantic proportions

Image: Henning Larsen Architects

The town of Lund, in Sweden, is already home to a number of major scientific facilities, including one of the most advanced synchrotron X-ray sources, the MAX IV, scheduled for inauguration in 2016. Now Lund will also be the site of the world's most powerful neutron source, the €1.8 billion European Spallation Source (ESS).

More than a dozen European countries are funding the project. (Sweden, with 35 percent and Denmark with 12.5 percent are the largest backers.) First light is expected in 2019.

The first neutron sources used for research consisted of nuclear reactors, but spallation sources don't have the safety issues of reactors and produce a much larger quantity of useful neutrons, says Henning Friis Poulsen, a physicist at the Technical University of Denmark in Kongens Lyngby.

As with all instruments for probing the smallest constituents of matter, the ESS will have gigantic proportions. A 600-meter long linear accelerator will propel protons that smash with a power of 5 MW into a rotating tungsten target. The protons, traveling at nearly the speed of light, hit the tungsten nuclei and eject neutrons, a process called spallation. The neutrons are then "cooled," or slowed down, and will be ultimately directed into 44 beam lines, all of which to be completed by 2025.

Poulsen says the combination of a new source with new designs of instruments will result in a significant performance improvement, which he estimates to be a factor between 30 and a thousand. "This means that you can perform experiments much better and much faster," he says. In some areas, such as research in superconductivity, where large samples were required up to now, the ESS will allow the use of smaller samples that are much easier to produce. "We will get some unique opportunities to understand these materials and others much better," he says.

Because neutrons have no charge, they don't scatter on electrons and can penetrate deep into atoms and probe atomic nuclei directly, which is not possible with X-rays. According to Poulsen, two factors make neutrons especially interesting. With X-rays you only "see" the heavy elements, but with neutrons, which interact with light elements such as hydrogen and carbon, you can probe a wider range of materials, with applications in molecular biology, biomedical research, and even food science.

The second factor is that neutrons carry a magnetic moment—they are tiny magnets. "They are an extremely good probe for magnetism," Poulsen says, adding that neutrons interact with the magnetic moments of atoms and may assist researchers investigating materials like superconductors.

The fact that neutrons can penetrate matter much better than X-rays makes them also interesting for engineering applications. If you want to look into a complete motor block, for example, using neutrons is much better than X-rays, he says.

The ESS and the MAX IV facilities will only be a kilometer apart. Their proximity, and the complementarity of the information obtained with X-rays and neutrons, should prove useful for researchers who want to study samples in both facilities. The ESS will employ a staff of 500 people and expects between 2000 and 5000 scientists to visit the facility every year.

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