How does BER II work
Neutrons are a part of our matter. They 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 are split.
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 is 10 megawatts. This is dissipated by cooling. A portion of the neutrons is needed to keep the chain reaction going. The remaining portion, however, is guided through so-called beam tubes to the experimental stations.
The experimental infrastructure
The experiments are housed in three halls. The first hall, known simply as the experimental hall, runs all the way around BER II. The beamlines come directly out of the wall of the reactor basin and are connected directly to the experimental infrastructure, so the experiments are set up closely along the edge of the basin. The neutrons that arrive here are moving very fast and are therefore very energy-rich. They are known as thermal neutrons.
A large portion of the neutrons, however, are redirected through a special conical beamline into so-called neutron guides. Here, they are slowed down so that they can continue on as cold neutrons to the more distant neutron guide halls I and II.
The cold source
The neutrons are slowed down using extremely cold hydrogen. This is kept in a special vessel built into the conical beamline. This component is therefore known as the “cold source”. In it, the neutrons run 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.