8.2.1 Positron emission and radionuclides

The positron is the antiparticle of the electron: it is identical to an electron in all of its properties, except that the sign of its electric charge and its magnetic moment is opposite to that of an electron. Positrons are denoted by the symbol e ⁺ or more frequently ? ⁺: they can be generated via the decay of several nuclei whose instability is due to an excessive number of protons with respect to the number of neutrons. These kinds of nuclei are inclined to adopt a more stable energetic configuration, by reducing the number of protons through the ? ⁺ decay (Fig. 8.4)

Figure 8.4: Diagrams of ? ⁺ decay: the nucleus of the ? ⁺ source _z N is unstable, by having an excessive number of protons with respect to neutrons. The nucleus reaches a more stable and lower energy configuration by reducing the proton number via positron emission; a neutrino is also emitted. The mass balance Q, which represents the released energy, is given by the sum of the kinetic energies of the positron and of the neutrino plus twice the electron rest mass. If the daughter nucleus is created...