![]() Because neither an electron nor a positron contains protons or neutrons, its mass number is 0. Like the notation used to indicate isotopes, the upper left superscript in the symbol for a particle gives the mass number, which is the total number of protons and neutrons. Table 20.1 Nuclear Decay Emissions and Their Symbols Identity Because the neutron-to-proton ratio in an α particle is 1, the net result of alpha emission is an increase in the neutron-to-proton ratio. Such nuclei tend to decay by emitting an α particle (a helium nucleus, H 2 4 e), which decreases the number of protons and neutrons in the original nucleus by 2. This is presumably due to the cumulative effects of electrostatic repulsions between the large number of positively charged protons, which cannot be totally overcome by the strong nuclear force, regardless of the number of neutrons present. With very few exceptions, heavy nuclei (those with A ≥ 200) are intrinsically unstable regardless of the neutron-to-proton ratio, and all nuclei with Z > 83 are unstable. ![]() These nuclei decay by processes that have the net effect of converting a proton to a neutron, thereby increasing the neutron-to-proton ratio. Nuclei on the lower right side of the band of stable nuclei have a neutron-to-proton ratio that is too low to give a stable nucleus. These nuclei decay by a process that converts a neutron to a proton, thereby decreasing the neutron-to-proton ratio. ![]() The nuclei on the upper left side of the band of stable nuclei in Figure 20.2 "The Relationship between Nuclear Stability and the Neutron-to-Proton Ratio" have a neutron-to-proton ratio that is too high to give a stable nucleus. The three general classes of radioactive nuclei are characterized by a different decay process or set of processes: We begin this section by considering the different classes of radioactive nuclei, along with their characteristic nuclear decay reactions and the radiation they emit. As we shall see, nuclear decay reactions occur spontaneously under all conditions, but nuclear transmutation reactions occur only under very special conditions, such as the collision of a beam of highly energetic particles with a target nucleus or in the interior of stars. In contrast, in a nuclear transmutation reaction A nuclear reaction in which a nucleus reacts with a subatomic particle or another nuleus to give a product nucleus that is more massive than the starting material., a nucleus reacts with a subatomic particle or another nucleus to form a product nucleus that is more massive than the starting material. ![]() The resulting daughter nuclei have a lower mass and are lower in energy (more stable) than the parent nucleus that decayed. In a nuclear decay reaction A nuclear reaction that occurs when an unstable nucleus emits radiation and is transformed into the nucleus of one or more other elements., also called radioactive decay, an unstable nucleus emits radiation and is transformed into the nucleus of one or more other elements. The two general kinds of nuclear reactions are nuclear decay reactions and nuclear transmutation reactions. To know the different kinds of radioactive decay. ![]()
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