What is radioactivity

Radioactivity is the physical process of spontaneous transformations of atomic nuclei. Initial nucleus is called mother, or parent nucleus. Correspondent radionuclide is also called mother (parent) one. The nucleus appeared because of radioactive transformation is called the daughter nucleus, or progeny nucleus. The same name the resulting radionuclide has. Mother and daughter nuclei and the radionuclides composed from them are called being genetically connected. If the daughter nucleus is radioactive, they say about radioactive transformation chains, or about radioactive series (families). All elements within radioactive series are also called genetically connected ones.

At alpha-decay (denoted a) a nucleus emits the nucleus of  ⁴He, that is called the a-particle.

The following spontaneous processes are related to beta-transformations:

• ß^--transformation (ß^--decay) is the spontaneous emission of the pair  «electron and electronic antineutrino» by a nucleus;
• ß⁺- transformation (ß⁺-decay) is the spontaneous emission of the pair  «positron and electronic neutrino» by a nucleus;
• е-capture, electronic capture (e) is the phenomenon of spontaneous capture of an electron from an atomic electron shell (more often from К-shell; that if why the term К-capture is frequently used) accompanying  by emission of the electronic neutrino;
• g-radiation (g) is the process of spontaneous emission by a nucleus of a photon (several photons) having energies referred to the ionising radiation.

Transitions of nuclei from long-living states (with average life-time more than 100 ns) to lower energy levels are called isomeric transitions (IT), and nuclei having long-living states are called isomers. The isomers’ excitation can be released not only due to electromagnetic interactions but also by emission of alpha-particles, beta-particles or other ones at some conditions being likely taken place.

Except these processes the following phenomena are referred to the radioactivity phenomena:

• spontaneous fission (denoted by f from the word fission) is the spontaneous fission of heavy nuclei onto two fragments having comparable masses (seldom there are three or even more of them);
• cluster activity is the spontaneous emission of nuclei heavier than ⁴He named nuclei-clusters (the clusters up to ³²S are discovered for today);
• neutron activity (n) is the spontaneous emission of neutrons by nuclei (it takes place among light nuclei overloaded by neutrons, e.g. ⁵He, or ¹⁰Li)
• proton activity (p) is the spontaneous emission of protons by nuclei (e.g., ¹¹²Cs, ¹³⁵Tb; the most heavy is ¹⁸⁵Bi);
• beta-delayed transformations – is the spontaneous emission of neutrons (ßn,ß2n), protons (ßp,ep,e2p), alpha-particles (ßa,ea) by nuclei, or beta-delayed spontaneous fission of super heavy nuclei (ßbf,ef). They take place at highly excited states od daughter nuclei, occurring in beta-transformations. The typical example is the emission of delayed neutrons by heavy nuclei fission fragments.

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Sometimes, the following additional beta-transformation processes are indicated.

• Beta-transformation of «bare» nuclei is the spontaneous ß^--transformation in highly ionised atom having half-life different (sometimes, quite different) from the half-life of the corresponding neutral atom. For example, the half-life of ¹⁸⁷Re in neutral atom is 5×10¹⁰ years, but for the totally ionised ¹⁸⁷Re it is less in 9 degrees. In multi charged radioactive ions there is bound beta-transformation, that is spontaneous emission by nuclei the pair «electron – antineutrino» with the consequent capture of the emitted electron by an electron shell of the atom (denoted b_b).
• Doubled beta-transformations are emission of two pairs of «electron –antineutrino» (2ß^-), or two pairs of «positron – neutrino» (2ß⁺), or doubled electronic capture (2e),  or electron capture with positron emission (eß⁺). These processes are very rare and have the most long half-lives that are known for today (from 7×10¹⁸ years for ¹⁰⁰Ru to (3,5±2,0)⋅10²⁴ years for ¹²⁸Te).

Rigorously saying, the fission fragments, alpha-particles and clusters, protons and neutrons appeared in different kinds of radioactivity phenomena can be considered as compartments of atomic nuclei but with some clauses (one should consider them as virtual particles). Electrons and antineutrinos as well as positrons and neutrinos are not the nucleus compartments and also are not the nucleon compartments. Gamma- radiation of nuclei happen in result of electromagnetic transitions in nuclei, and, therefore, they are not to be referred to the nuclear decays. Thus, the term “decay” habitual in scientific and public use is not worth to treat literary to the radioactivity phenomenon, but it should be considered as synonym of the term “transformation”. In such sense, the terms “beta-decay”, “gamma-decay” should be treated.
Electromagnetic quantum transitions in nuclei may be accompanied by the internal conversion (an atom emits an electron from its electron shell except emitting photon, Fig. 6), or pair conversion (the forming of electron-positron pair except gamma-quantum). But these phenomena are not considered as separate kinds of radioactivity.
Thus, radioactivity should be treated as the atomic phenomena linked with atomic nuclear transformations.
Some radionuclides demonstrate two (e.g., a- and ß^- of ²¹²Bi, ß^- and e of ⁴⁰K and ⁶⁴Cu, p and a of ¹⁸⁵Bi) and even three kinds of radioactivity (e.g., a, e and ep of ¹¹⁰Xe, ß^-, ß^-n and ß^-2n of ⁹⁸Rb, e, ep and e2p  of ³⁵Ca), happened with different likelihood. In these cases they say that such radionuclides are able to undergo radioactive transformations along different modes.


Three frequently met primordial chains: