This is how ESS works

The European Spallation Source, or ESS research facility, comprises a neutron source that could be described as an enormous microscope for examining molecular structures. The facility will make it possible to study materials in their smallest components and is consequently useful in materials research in diverse fields such as medicine, biology, chemistry, physics and engineering.

A particle accelerator produces a beam of protons, that is, the nucleus of a hydrogen atom with a high level of kinetic energy (2.5 gigaelectronvolts, GeV) and a high beam power (5 megawatts, MW). The protons are shot at a beam target of tungsten; the nuclear reactions when the protons collide with the tungsten atoms form neutrons. The neutrons are slowed down to low energies for subsequent use in experiments where different materials can be studied at experiment stations using special instruments.

There are applications in broad disciplines such as medicine, chemistry, physics and engineering.