Survey of Nuclear Decay Types

Nuclei can emit radiation spontaneously. The general process is called radioactive decay. While this subject will be discussed in detail in Chapters 3, 7, 8, and 9, we need to know a few general ideas about these processes right away (which we can summarize below). 

Radioactive decay usually involves one of three basic types of decay, a decay, (3 decay, or y decay in which an unstable nuclide spontaneously changes into a more stable form and emits some radiation. In Table 1.1, we summarize the basic features of these decay types. 

The fact that there were three basic decay processes (and their names) was discovered by Rutherford. He showed that all three processes occur in a sample of decaying natural uranium (and its daughters). The emitted radiations were designated a, (3, and y to denote the penetrating power of the different radiation types. Further research has shown that in a decay, a heavy nucleus spontaneously emits a 4He nucleus (an a particle). The emitted a particles are monoenergetic, and, as a result of the decay, the parent nucleus loses two protons and two neutrons and is transformed into a new nuclide. All nuclei with Z 83 are unstable with respect to this decay mode. 

Nuclear electromagnetic decay occurs in two ways, y decay and internal conversion (IC). In y-ray decay a nucleus in an excited state decays by the emission of a photon. In internal conversion the same excited nucleus transfers its energy radia-tionlessly to an orbital electron that is ejected from the atom. In both types of decay, only the excitation energy of the nucleus is reduced with no change in the number of any of the nucleons. 

Sample Problem 1.2 Because of the conservation of the number of nucleons in the nucleus and conservation of charge during radioactive decay (Table 1.1), 

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