ABSTRACT
The neutron was discovered in 1932. The following years witnessed intense study of its properties and interactions with matter. This neutral particle is about 2000 times the mass of an electron and is scattered and absorbed by different materials. The nature and rate of its reaction are determined by the nuclei of the host material and the energy of the neutron. Moreover, the nuclei that absorb neutrons can become radioactive and be transmuted to other types of nuclei, through radioactive decays. Neutrons can also split (ssion) some nuclei (the ssile isotopes such as U-233, U-235, and Pu-239). Such ssion is a complex process that produces new nuclei, beta and gamma radiation, and a few neutrons themselves. The products are energetic (the kinetic energy of ssion products, energy of radiation), deriving their energy from the binding energy of the nucleus. Consequently, the new neutrons (two to three on average) released in ssion provide the basis for a chain reaction. This chain reaction can be sustained (each successive generation has the same number of neutrons) or multiplied (each successive generation has more neutrons), and it can be used for a controlled and a sustained as well as an explosive release of energy.1-21
Fission of a single nucleus releases about 200 MeV (3.2 × 10−11 J) of energy. This energy is distributed, in a power reactor of modern design, approximately as shown in Table 18.1 and Figure 18.1.
