The law of radioactive displacements, also known as Fajans's and Soddy's law, in radiochemistry and

nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies th ...

, is a rule governing the transmutation of elements during

radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

. It is named after Frederick Soddy and Kazimierz Fajans, who independently arrived at it at about the same time in 1913.Frederick Soddy, "The Radio Elements and the Periodic Law", Chem. News, Nr. 107, 1913, pp. 97–99 The law describes which

chemical element A chemical element is a chemical substance whose atoms all have the same number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its ...

and

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

is created during the particular type of radioactive decay: * In

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an a ...

, an element is created with an

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of pro ...

less by 2 and a

mass number The mass number (symbol ''A'', from the German word: ''Atomgewicht'', "atomic weight"), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is appro ...

less by four of that of the parent radioisotope, e.g.: ::

^_\text\to^_\text

* In

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

, the mass number remains unchanged while the atomic number becomes greater by 1 than that of the parent radioisotope, e.g.: ::

^_\text\to^_\text

*This corresponds to β⁻ decay or electron emission, the only form of beta decay which had been observed when Fajans and Soddy proposed their law in 1913. Later, in the 1930s, other forms of beta decay known as β⁺ decay (

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron emi ...

) and

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

were discovered, in which the atomic number becomes less by 1 than that of the parent radioisotope, e.g.: ::

^_\text\to^_\text

References

{{Reflist Eponymous laws of physics Radiochemistry Nuclear physics

See also

References