How does ESS work?

Photo credit: ESS AB
http://ess-scandinavia.eu/

At HZB, the neutrons researchers use to look inside materials are produced by the neutron source BER II by nuclear fission. A completely different process is used to produce neutrons at ESS.

Here, neutrons are obtained by “spallation”. For this purpose, first protons (the positive particles of the atomic nucleus) are accelerated, to near light speed. The protons are then guided onto a heavy metal target. The impact causes neutrons to be ejected. At the same time, the atom nuclei in the metal block excited by the collision with the high-energy protons become so energetic that more neutrons “steam off”. This effect produces the most scientifically useful neutrons. However, they are still too fast (too energetic) at this stage.

For these neutrons to be useful for measurements, they first have to be slowed down in tanks of water or liquid hydrogen that surround the target. Finally, the neutrons are guided through neutron optical systems to the experimental stations.