Decay chain

Nuclear physics
Nucleus Nucleons p n Nuclear matter Nuclear force Nuclear structure Nuclear reaction
Models of the nucleus Liquid drop Nuclear shell model Interacting boson model Ab initio
Nuclides' classification Isotopes – equal Z Isobars – equal A Isotones – equal N Isodiaphers – equal N − Z Isomers – equal all the above Mirror nuclei – Z ↔ N Stable Magic Even/odd Halo Borromean
Nuclear stability Binding energy p–n ratio Drip line Island of stability Valley of stability Stable nuclide
Radioactive decay Alpha α Beta β 2β 0v β+ K/L capture Isomeric Gamma γ Internal conversion Spontaneous fission Cluster decay Neutron emission Proton emission Decay energy Decay chain Decay product Radiogenic nuclide
Nuclear fission Spontaneous Products pair breaking Photofission
Capturing processes electron 2× neutron s r proton p rp
High-energy processes Spallation by cosmic ray Photodisintegration
Nucleosynthesis and nuclear astrophysics Nuclear fusion Processes: Stellar Big Bang Supernova Nuclides: Primordial Cosmogenic Artificial
High-energy nuclear physics Quark–gluon plasma RHIC LHC
Scientists Alvarez Becquerel Bethe A. Bohr N. Bohr Chadwick Cockcroft Ir. Curie Fr. Curie Pi. Curie Skłodowska-Curie Davisson Fermi Hahn Jensen Lawrence Mayer Meitner Oliphant Oppenheimer Proca Purcell Rabi Rutherford Soddy Strassmann Świątecki Szilárd Teller Thomson Walton Wigner
Physics portal  Category
v t e

In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". The typical radioisotope does not decay directly to a stable state, but rather it decays to another radioisotope. Thus there is usually a series of decays until the atom has become a stable isotope, meaning that the nucleus of the atom has reached a stable state.

Decay stages are referred to by their relationship to previous or subsequent stages. A parent isotope is one that undergoes decay to form a daughter isotope. One example of this is uranium (atomic number 92) decaying into thorium (atomic number 90). The daughter isotope may be stable or it may decay to form a daughter isotope of its own. The daughter of a daughter isotope is sometimes called a granddaughter isotope. Note that the parent isotope becomes the daughter isotope, unlike in the case of a biological parent and daughter.

The time it takes for a parent atom to decay to its daughter nuclei can vary widely, based on the material's half-life. For individual nuclei, the process behaves as a random Poisson process, as the decay of each single atom occurs spontaneously.

The decay of an initial population of identical atoms over time t follows a decaying exponential distribution e^−λt, where λ is the decay constant. An important property of a radioactive material is its half-life, the time by which half of an initial number of identical parent radioisotopes can be expected statistically to have decayed to their daughters, which is inversely related to λ. Half-lives have been determined in laboratories for many radionuclides, and can range from nearly instantaneous (less than 10⁻²¹ seconds) to more than 10¹⁹ years.

At equilibrium, each intermediate stage of the decay chain emit the same amount of radioactivity as the original radioisotope (i.e., a one-to-one relationship between the numbers of decays in each successive stage). However each stage can release a different quantity of energy, as the decay energy is specific to each radionuclide. If and when equilibrium is achieved, each successive daughter isotope is present in direct proportion to its half-life; but since its activity is inversely proportional to its half-life, each nuclide in the decay chain contributes as many individual transformations as the head of the chain. For example, uranium-238 is weakly radioactive, but pitchblende, a uranium ore, is 13 times more radioactive than the pure uranium metal because of the presence of shorter-lived decay products, such as radium and the noble gas radon. Rock containing thorium and/or uranium (such as some types of granite) emits radon gas, which tends to accumulate in enclosed places such as basements or underground mines due to its high density.^[1]

The quantity of isotopes in the decay chains at a certain time is described by the Bateman equation. Due to its peculiarities, isotopically enriched materials out of equilibrium with its natural decay products can occasionally increase in radioactivity for an amount of time, contrary to common intuition about radioactive decay.^[2] Depleted uranium is an example of such material.