Neutrons and protons build the nucleus of each atom except the hydrogen, whose nucleus is a single proton. Thus almost half of the known matter consists of neutrons. The nucleus is circled by electrons. Compared to the whole atom, the nucleus is the size of a rice corn in comparison to a football arena.

Not only because they are so small, neutrons were only discovered very late in the year 1932 (Discovery of the neutrons), also the generation of free neutrons, meaning the extraction of the small particles from the nucleus, was successfully managed by Otto Hahn and Lise Meitner in 1938 (Neutron sources).

The field of application of neutrons is huge. Neutrons have many advantageous properties: They bear for example a magnetic moment, but are electrically neutral (Why neutrons?).