Docentship lecture: The neutron – neutral, fickle, and useful

Chairperson: professor Stephan Pomp

Representative of the Docentship Committee: professor Carlos Perez de los Heros

Abstract: The neutron is an uncharged particle with similar weight as the proton. The existence of the neutron was experimentally proven 1932 by James Chadwick. Ernest Rutherford had, however, previously theorized about and named this particle already during the 1920:s. The neutrons play a central role in both current and future nuclear reactor concepts, such as fusion reactors and fission reactors of generation IV.

In today’s fission reactors, neutrons cleave (fission) uranium nuclei. As nuclei are fissioned two fission products are produced and energy is released. In addition, about two to three neutrons are produced in the process. When precisely one of these new neutrons fission another uranium nucleus, we can achieve a stable process (a controlled chain reactions) where each consecutive fission leads to another fission and so on. In this way, we can create a continuous process which releases energy steadily over time.

In fusion power plants hydrogen atoms will be fused to release energy. The hydrogen isotopes deuterium and tritium are the most prominent candidates. Deuterium is generously available in the world, for example in the seas. Tritium, however, decays with a half-life of about 12 years. This forces us to produce tritium to allow for its usage as fuel in the fusion reactor. As deuterium and tritium fuses a neutron and a helium nucleus is produced. The neutron will carry large parts of the released energy as kinetic energy and will leave the reactor. The neutron will then deposit its energy in surrounding material. This energy deposition serves two parts: partly for the harnessing of the released energy from the reactor to produce electricity and, partly, to produce more tritium to be injected into the reactor.

During this lecture, I will tell you about the discovery of the neutron and give an overview of its importance in the applications given above. I will also explain how we measure the neutron energy distributions from fusion reactors to draw conclusions about what is happening inside the reactor. In addition, I will explain the importance of studying the probabilities of neutron interactions in materials.

The lecture is an obligatory teaching test for those applying for admittance as docent and it should be possible for students and others with basic academic education in the relevant field to follow it. The lecture lasts 40-45 minutes with subsequent discussion. The lecture will be given in Swedish.

Welcome!