How did BER II work?

Neutrons are components of every atomic nucleus. They are tightly bound within it; only a few materials neutrons can released from. In BER II, uranium nuclei were split.

Nuclear fission

Fission, or splitting, occurs as a chain reaction: when a slow-moving neutron collides with the nucleus of a uranium atom, the neutron is absorbed and the nucleus breaks apart. This splitting results in several fission products including, among others, neutrons, lighter atomic nuclei, radioactivity and heat.

The heat power generated at BER II was 10 megawatts. This was dissipated by cooling. A portion of the neutrons was needed to keep the chain reaction going. The remaining portion, however, was guided through so-called beam tubes to the experimental stations.

The experimental infrastructure

High field magnet at the neutron source BER II © HZB/Kevin Fuchs

The cold source

The neutrons were slowed down using extremely cold hydrogen. This was kept in a special vessel built into the conical beamline. This component was therefore known as the “cold source”. In it, the neutrons ran into the hydrogen atoms, thereby losing a lot of energy.

The ability to experiment with cold neutrons opened up many new possibilities for neutron-based materials research. The work at BER II contributed significantly to this. It allowed, for example, even plastics and biological macromolecules to be studied with neutrons.