View source for Decay chain

{{Short description|Series of radioactive decays}}
{{Nuclear physics}}

In [[nuclear science]] a '''decay chain''' refers to the predictable series of [[radioactive decay|radioactive disintegration]]s undergone by the nuclei of certain unstable chemical elements. 

[[Radionuclide|Radioactive isotopes]] do not usually decay directly to [[stable isotopes]], but rather into another radioisotope. The isotope produced by this radioactive emission then decays into another, often radioactive isotope. This chain of decays always terminates in a [[Stable nuclide|stable isotope]], whose nucleus no longer has the surplus of energy necessary to produce another emission of radiation. Such stable isotopes are then said to have reached their ''[[Ground state|ground states]]''.

The stages or steps in a decay chain are referred to by their relationship to previous or subsequent stages. Hence, a ''parent isotope'' is one that undergoes decay to form a ''daughter isotope''. For example element 92, [[uranium]], has an isotope with 144 neutrons ([[Uranium-236|<sup>236</sup>U]]) and it decays into an isotope of element 90, [[thorium]], with 142 neutrons ([[Isotopes of thorium|<sup>232</sup>Th]]). The daughter isotope may be stable or it may itself decay to form another daughter isotope. <sup>232</sup>Th does this when it decays into [[Isotopes of radium|radium-228]]. The daughter of a daughter isotope, such as <sup>228</sup>Ra, is sometimes called a ''granddaughter isotope''. <sup>228</sup>Ra in turn undergoes a further eight decays and [[Nuclear transmutation|transmutations]] until a stable isotope, [[Lead-208|<sup>208</sup>Pb]], is produced, terminating the decay chain of <sup>236</sup>U. 

The time required for an atom of a parent isotope to decay into its daughter is fundamentally unpredictable and varies widely. For individual nuclei the process is [[Uncertainty principle|not known to have determinable causes]] and the time at which it occurs is therefore [[Poisson point process|completely random]]. The only prediction that can be made is statistical and expresses an average rate of decay. This rate can be represented by adjusting the curve of a decaying [[exponential distribution]] with a [[decay constant]] (''λ'') particular to the isotope. On this understanding the radioactive decay of an initial population of unstable atoms over time ''t'' follows the curve given by ''[[E (mathematical constant)|e]]''<sup>−''λt''</sup>.

One of the most important properties of any radioactive material follows from this analysis, its [[half-life]]. This refers to the time required for half of a given number of radioactive atoms to decay and is inversely related to the isotope's decay constant, ''λ''. Half-lives have been determined in laboratories for many radionuclides, and can [[List of radioactive nuclides by half-life|range]] from nearly instantaneous—[[Isotopes of hydrogen|hydrogen-5]] decays in less [[Speed of light|time than it takes]] for a photon to go from one end of its nucleus to the other—to fourteen [[Orders of magnitude (time)|orders of magnitude]] longer than the [[age of the universe]]: [[Isotopes of tellurium|tellurium-128]] has a half-life of {{val|2.2|e=24|u=years}}.

[[File:DecayChain241Pu-eng.svg|thumb|Quantity calculation with the Bateman-Function for <sup>241</sup>Pu]]
The [[Bateman equation]] predicts the relative quantities of all the isotopes that compose a given decay chain once that decay chain has proceeded long enough for some of its daughter products to have reached the stable (i.e., nonradioactive) end of the chain. A decay chain that has reached this state, which may require billions of years, is said to be in ''equilibrium''. A sample of radioactive material in ''equilibrium'' produces a steady and steadily decreasing quantity of radioactivity as the isotopes that compose it traverse the decay chain. On the other hand, if a sample of radioactive material has been isotopically enriched, meaning that a radioisotope is present in larger quantities than would exist if a decay chain were the only cause of its presence, that sample is said to be ''out of equilibrium''. An unintuitive consequence of this disequilibrium is that a sample of [[Nuclear enrichment|enriched]] material may occasionally increase in radioactivity as daughter products that are more highly radioactive than their parents accumulate. Both [[Enriched uranium|enriched]] and [[Depleted uranium|depleted]] uranium provide examples of this phenomenon.

== History ==
The chemical elements came into being in two phases. The first commenced shortly after the [[Big Bang]]. From ten seconds to 20 minutes after the beginning of the universe the [[Big Bang nucleosynthesis|earliest condensation of light atoms]] was responsible for the manufacture of the four lightest elements. The vast majority of this primordial production consisted of the three lightest isotopes of [[hydrogen]]—[[Isotopes of hydrogen|protium]], [[deuterium]] and [[tritium]]—and two of the nine known isotopes of [[helium]]—[[helium-3]] and [[helium-4]]. Trace amounts of [[Isotopes of lithium#Lithium-7|lithium-7]] and [[Isotopes of beryllium#Beryllium-7|beryllium-7]] were likely also produced. 

So far as is known, all heavier elements came into being starting around 100 million years later, in a second phase of [[nucleosynthesis]] that commenced with the birth of the [[Primordial star|first stars]].<ref>{{Cite web |last=Bromm |first=Richard B. Larson, Volker |title=The First Stars in the Universe |url=https://www.scientificamerican.com/article/the-first-stars-in-the-un/ |access-date=2024-09-29 |website=Scientific American |language=en}}</ref> The nuclear furnaces that power stellar evolution were necessary to create large quantities of all elements heavier than helium, and the [[R-process|r-]] and [[s-process]]<nowiki/>es of neutron capture that occur in stellar cores are thought to have created all such elements up to [[iron]] and [[nickel]] (atomic numbers 26 and 28). The [[Supernova nucleosynthesis|extreme conditions]] that attend [[Supernova|supernovae]] explosions are capable of creating the elements between [[oxygen]] and [[rubidium]] (i.e., atomic numbers 8 through 37). The creation of heavier elements, including those without stable isotopes—all elements with atomic numbers greater than lead's, 82—appears to rely on r-process nucleosynthesis operating amid the immense concentrations of free neutrons released during [[Neutron star merger|neutron star mergers]].

Most of the isotopes of each chemical element present in the Earth today were formed by such processes no later than the time of [[History of Earth|our planet's condensation]] from the solar [[Protoplanetary disk|protoplanetary disc]], around 4.5 billion years ago. The exceptions to these so-called ''primordial'' elements are those that have resulted from the radioactive disintegration of unstable parent nuclei as they progress down one of several decay chains, each of which terminates with the production of one of the 251 stable isotopes known to exist. Aside from cosmic or stellar nucleosynthesis, and decay chains the only other ways of producing a chemical element rely on [[Nuclear weapon|atomic weapons]], nuclear reactors ([[Natural nuclear fission reactor|natural]] or [[Nuclear reactor|manmade]]) or the laborious atom-by-atom [[Superheavy element|assembly]] of nuclei with [[Particle accelerator|particle accelerators]].

Unstable isotopes decay to their daughter products (which may sometimes be even more unstable) at a given rate; eventually, often after a series of decays, a stable isotope is reached: there are 251 stable isotopes in the universe. In stable isotopes, light elements typically have a lower ratio of neutrons to protons in their nucleus than heavier elements. Light elements such as [[helium-4]] have close to a 1:1 neutron:proton ratio. The heaviest elements such as uranium have close to 1.5 neutrons per proton (e.g. 1.587 in [[uranium-238]]). No nuclide heavier than lead-208 is stable; these heavier elements have to shed mass to achieve stability, mostly by [[alpha decay]]. The other common way for isotopes with a high neutron to proton ratio (n/p) to decay is [[beta decay]], in which the nuclide changes elemental identity while keeping the same mass number and lowering its n/p ratio. For some isotopes with a relatively low n/p ratio, there is an [[positron emission|inverse beta decay]], by which a proton is transformed into a neutron, thus moving towards a stable isotope; however, since fission almost always produces products which are neutron heavy, [[positron emission]] or [[electron capture]] are rare compared to electron emission. There are many relatively short beta decay chains, at least two (a heavy, beta decay and a light, [[positron]] decay) for every discrete weight up to around 207 and some beyond, but for the higher mass elements (isotopes heavier than lead) there are only four pathways which encompass all decay chains.{{Citation needed|date=July 2023}} This is because there are just two main decay methods: [[alpha radiation]], which reduces the mass number by 4, and beta, which leaves it unchanged. The four paths are termed 4n, 4n&nbsp;+&nbsp;1, 4n&nbsp;+&nbsp;2, and 4n&nbsp;+&nbsp;3; the remainder from dividing the atomic mass by four gives the chain the isotope will follow in its decay. There are other decay modes, but they invariably occur at a lower probability than alpha or beta decay. (It should not be supposed that these chains have no branches: the diagram below shows a few branches of chains, and in reality there are many more, because there are many more isotopes possible than are shown in the diagram.) For example, the third atom of [[nihonium-278]] synthesised underwent six alpha decays down to [[mendelevium-254]], followed by an [[electron capture]] (a form of beta decay) to [[fermium-254]], and then a seventh alpha to [[californium-250]],<ref>{{cite journal|journal=Journal of the Physical Society of Japan|volume=81|article-number=103201 |date=2012|title=New Results in the Production and Decay of an Isotope, <sup>278</sup>113, of the 113th Element|author=K. Morita|doi=10.1143/JPSJ.81.103201|last2=Morimoto|first2=Kouji|last3=Kaji|first3=Daiya|last4=Haba|first4=Hiromitsu|last5=Ozeki|first5=Kazutaka|last6=Kudou|first6=Yuki|last7=Sumita|first7=Takayuki|last8=Wakabayashi|first8=Yasuo|last9=Yoneda|first9=Akira|first10=Kengo |last10=Tanaka|first11=Sayaka |last11=Yamaki|first12=Ryutaro |last12=Sakai|first13=Takahiro |last13=Akiyama|first14=Shin-ichi |last14=Goto|first15=Hiroo |last15=Hasebe|first16=Minghui |last16=Huang|first17=Tianheng |last17=Huang|first18=Eiji |last18=Ideguchi|first19=Yoshitaka |last19=Kasamatsu|first20=Kenji |last20=Katori|first21=Yoshiki |last21=Kariya|first22=Hidetoshi |last22=Kikunaga|first23=Hiroyuki |last23=Koura|first24=Hisaaki |last24=Kudo|first25=Akihiro |last25=Mashiko|first26=Keita |last26=Mayama|first27=Shin-ichi |last27=Mitsuoka|first28=Toru |last28=Moriya|first29=Masashi |last29=Murakami|first30=Hirohumi |last30=Murayama|first31=Saori |last31=Namai|first32=Akira |last32=Ozawa|first33=Nozomi |last33=Sato|first34=Keisuke |last34=Sueki|first35=Mirei |last35=Takeyama|first36=Fuyuki |last36=Tokanai|first37=Takayuki |last37=Yamaguchi|first38=Atsushi |last38=Yoshida
|issue=10|display-authors=10|arxiv = 1209.6431 |bibcode = 2012JPSJ...81j3201M |s2cid=119217928 }}</ref> upon which it would have followed the 4n&nbsp;+&nbsp;2 chain (radium series) as given in this article. However, the heaviest [[superheavy element|superheavy]] nuclides synthesised do not reach the four decay chains, because they reach a [[spontaneous fission|spontaneously fissioning]] nuclide after a few alpha decays that terminates the chain: this is what happened to the first two atoms of nihonium-278 synthesised,<ref name="Nh278 04Mo01">{{cite journal|title=Experiment on the Synthesis of Element 113 in the Reaction <sup>209</sup>Bi(<sup>70</sup>Zn, n)<sup>278</sup>113|doi=10.1143/JPSJ.73.2593|year=2004|last1=Morita |first1=Kosuke |journal=Journal of the Physical Society of Japan |volume=73 |pages=2593–2596 |last2=Morimoto |first2=Kouji |last3=Kaji |first3=Daiya |last4=Akiyama |first4=Takahiro |last5=Goto |first5=Sin-Ichi |last6=Haba |first6=Hiromitsu |last7=Ideguchi |first7=Eiji |last8=Kanungo |first8=Rituparna |last9=Katori |first9=Kenji |last10=Koura |first10=Hiroyuki |last11=Kudo |first11=Hisaaki |last12=Ohnishi |first12=Tetsuya |last13=Ozawa |first13=Akira |last14=Suda |first14=Toshimi |last15=Sueki |first15=Keisuke |last16=Xu |first16=Hushan |last17=Yamaguchi |first17=Takayuki |last18=Yoneda |first18=Akira |last19=Yoshida |first19=Atsushi |last20=Zhao |first20=Yuliang |display-authors=8 |issue=10 |bibcode = 2004JPSJ...73.2593M |doi-access= }}</ref><ref name="JWP Nh278">{{cite journal |last1=Barber |first1=Robert C. |last2=Karol |first2=Paul J |last3=Nakahara |first3=Hiromichi |last4=Vardaci |first4=Emanuele |last5=Vogt |first5=Erich W. |title=Discovery of the elements with atomic numbers greater than or equal to 113 (IUPAC Technical Report)|doi=10.1351/PAC-REP-10-05-01 |journal=Pure and Applied Chemistry |year=2011 |volume=83|issue=7 |page=1485|doi-access=free }}</ref> as well as to all heavier nuclides produced.

Three of those chains have a long-lived isotope (or nuclide) near the top; this long-lived nuclide is a bottleneck in the process through which the chain flows very slowly, and keeps the chain below them "alive" with flow. The three long-lived nuclides are uranium-238 (half-life 4.463 billion years), uranium-235 (half-life 704 million years) and thorium-232 (half-life 14.1 billion years). The fourth chain has no such long-lasting bottleneck nuclide near the top, so that chain has long since decayed down to the last before the end: bismuth-209. This nuclide was long thought to be stable, but in 2003 it was found to be unstable, with a very long half-life of 20.1 billion billion years;<ref>{{Cite journal|author=J.W. Beeman|display-authors=et al|date=2012|title=First Measurement of the Partial Widths of <sup>209</sup>Bi Decay to the Ground and to the First Excited States|journal=Physical Review Letters |volume=108 |issue=6 |article-number=062501|doi=10.1103/PhysRevLett.108.062501|pmid=22401058|arxiv=1110.3138|s2cid=118686992 }}</ref> it is the last step in the chain before stable thallium-205. Because this bottleneck is so long-lived, very small quantities of the final decay product have been produced, and for most practical purposes bismuth-209 is the final decay product.

In the past, during the first few million years of the history of the Solar System, there were more unstable high-mass nuclides in existence, and the four chains were longer, as they included nuclides that have since decayed away. Notably, <sup>244</sup>Pu, <sup>237</sup>Np, and <sup>247</sup>Cm have half-lives over a million years and would have then been bottlenecks higher in the 4n, 4n+1, and 4n+3 chains respectively<ref name=Davis>{{cite journal |last1=Davis |first1=Andrew M. |date=2022 |title=Short-Lived Nuclides in the Early Solar System: Abundances, Origins, and Applications |journal=Annual Review of Nuclear and Particle Science |volume=72 |issue= |pages=339–363 |doi=10.1146/annurev-nucl-010722-074615 |doi-access=free |bibcode=2022ARNPS..72..339D }}</ref> - <sup>244</sup>Pu and <sup>247</sup>Cm have been identified as having been present. (There is no nuclide with a half-life over a million years above <sup>238</sup>U in the 4n+2 chain.) Today some of these formerly extinct isotopes are again in existence as they have been manufactured. Thus they again take their places in the chain: plutonium-239, used in nuclear weapons, is the major example, decaying to uranium-235 via alpha emission with a half-life 24,500 years. There has also been large-scale production of neptunium-237, resurrecting the extinct fourth chain.<ref>{{cite book|last1=Koch|first1=Lothar|title=Transuranium Elements, in Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley|date=2000|doi=10.1002/14356007.a27_167}}</ref> The tables below hence start the four decay chains at isotopes of [[californium]] with mass numbers from 249 to 252.

{|class=wikitable
|+Summary of the four decay chain pathways
|'''Name of series'''||Thorium||Neptunium||Uranium||Actinium
|-
|'''Mass numbers'''||4''n''||4''n''+1||4''n''+2||4''n''+3
|-
|'''Long-lived nuclide'''||<sup>232</sup>Th{{br}}(<sup>244</sup>Pu)||<sup>209</sup>Bi{{br}}(<sup>237</sup>Np)||<sup>238</sup>U{{br}}&nbsp;||<sup>235</sup>U{{br}}(<sup>247</sup>Cm)
|-
|'''Half-life'''<br/>(billions of years)||14.1{{br}}(0.0813)|| {{val|20100000000}}{{br}}(0.002144) ||4.463{{br}}&nbsp;||0.704{{br}}(0.0156)
|-
|'''End of chain'''||<sup>208</sup>Pb||<sup>205</sup>Tl||<sup>206</sup>Pb||<sup>207</sup>Pb
|}

These four chains are summarised in the chart in the following section.

== Types of decay ==
[[Image:Radioactive decay chains diagram.svg|thumb|right|350px| This diagram illustrates the four decay chains discussed in the text: thorium (4n, in blue), neptunium (4n+1, in pink), radium (4n+2, in red) and actinium (4n+3, in green).]] The four most common modes of radioactive decay are: alpha decay, beta decay, [[inverse beta decay]] (considered as both positron emission and electron capture), and [[isomeric transition]].  Of these decay processes, only alpha decay (fission of a [[helium-4]] nucleus) changes the [[atomic mass number]] (''A'') of the nucleus, and always decreases it by four. Because of this, almost any decay will result in a nucleus whose atomic mass number has the same [[modular arithmetic|residue]] mod 4. This divides the list of nuclides into four classes, each of which forms a main decay chain.

Three of these are readily observed in nature, commonly called the thorium series, the [[radium]] or uranium series, and the [[actinium]] series, representing three of these four classes, and ending in three different, stable isotopes of [[lead]]. The mass number of every isotope in the chain can be represented as ''A''&nbsp;=&nbsp;4''n'', ''A''&nbsp;=&nbsp;4''n''&nbsp;+&nbsp;2, or A&nbsp;=&nbsp;4''n''&nbsp;+&nbsp;3, respectively. The long-lived starting isotopes of these three isotopes, respectively [[thorium-232]], [[uranium-238]], and [[uranium-235]], have existed since the formation of the Earth, ignoring the artificial isotopes and their decays created since the 1940s.

Due to the relatively short [[half-life]] of its starting isotope [[neptunium-237]] (2.144 million years), the fourth chain, the [[neptunium]] series with ''A''&nbsp;=&nbsp;4''n''&nbsp;+&nbsp;1, is already extinct in nature, except for the final rate-limiting step, decay of [[bismuth-209]]. Traces of <sup>237</sup>Np and its decay products do occur in nature, however, as a result of neutron reactions in uranium ore; neutron capture by natural thorium to give <sup>233</sup>U is also possible.<ref name=4n1/> The ending isotope of this chain is now known to be [[thallium-205]]. Some older sources give the final isotope as bismuth-209, but in 2003 it was discovered that it is very slightly radioactive, with a half-life of {{val|2.01|e=19|u=years}}.<ref name=nubase>{{NUBASE2020}}</ref>

There are also non-transuranic decay chains of unstable isotopes of light elements, for example those of [[magnesium-28]] and [[chlorine-39]]. On Earth, most of the starting isotopes of these chains before 1945 were generated by [[cosmic radiation]]. Since 1945, the testing and use of nuclear weapons has also released numerous radioactive [[fission products]]. Almost all such isotopes decay by either β<sup>−</sup> or β<sup>+</sup> decay modes, changing from one element to another at the same atomic mass. The later daughter products in such a chain, being closer to beta-stability, generally have the longer half-lives.

== Heavy nuclei (actinide) decay chains ==
{{Actinidesvsfissionproducts}}
In the four tables below, very minor branches of decay (branching probability less than one in a million) are omitted. [[Spontaneous fission]] is also omitted, though larger than this for the heaviest even nuclei and detectable down to thorium. All nuclear data is taken from <ref name="nubase" /> unless otherwise noted. The historical names of isotopes are recorded in.<ref>{{Thoennessen2016|pages=19}}</ref>

The energy release includes the total kinetic energy of all the emitted particles ([[electron]]s, [[alpha particle]]s, [[Gamma rays|gamma quanta]], [[neutrino]]s, [[Auger electron]]s and [[X-ray]]s) and the recoiling decay product nucleus; this corresponds to that calculated from atomic masses. The letter 'a' represents a year (from the Latin ''[[:wikt:annus|annus]]'').

In the tables (except for the neptunium series), the historical names of the naturally occurring nuclides are also given. Such names were used at the time when the decay chains were first discovered and investigated; the system listed was only finalized in the 1920s but it would be too confusing to give earlier names also. From these historical names one can thus find the modern isotopic designation.

The three primordial chains given below—thorium, uranium/radium (from uranium-238), and actinium (from uranium-235)—each ends with its own specific lead isotope (lead-208, lead-206, and lead-207 respectively). All the lead isotopes are stable and are also present in nature as [[primordial nuclide]]s, so their excess amounts in comparison with lead-204 (which has only a primordial origin) are required for accurate [[uranium–lead dating]] of rocks. Correlating more than one results in [[lead-lead dating]], capable of even greater accuracy.
{{Clear}}

=== Thorium series ===
[[Image:Decay Chain Thorium.svg|thumb|300px|right]]
The 4n chain of thorium-232 is commonly called the "thorium series" or "thorium cascade". The series terminates with lead-208, 6 [[alpha decay]]s and 4 [[beta decay]]s from thorium.

Plutonium-244 (which appears several steps above thorium-232) was present in the early Solar System,<ref name=Davis/> and is just long-lived enough that it should still survive in trace quantities today,<ref name="PU244">{{cite journal | last1 = Hoffman | first1 = D. C. | last2 = Lawrence | first2 = F. O. | last3 = Mewherter | first3 = J. L. | last4 = Rourke | first4 = F. M. | year = 1971| title = Detection of Plutonium-244 in Nature | journal = [[Nature (journal)|Nature]] | volume =  234| issue = 5325 | pages =  132–134| doi = 10.1038/234132a0 | bibcode = 1971Natur.234..132H | s2cid = 4283169 }}</ref> though it probably has not been detected.<ref name="PRC">{{cite journal|last=Lachner|first=J.|display-authors=etal|date=2012|title=Attempt to detect primordial <sup>244</sup>Pu on Earth|journal=Physical Review C|volume=85|issue=1 |article-number=015801| doi=10.1103/PhysRevC.85.015801|bibcode=2012PhRvC..85a5801L}}</ref>

The total energy released from thorium-232 to lead-208, including the energy lost to neutrinos, is 42.65&nbsp;MeV; from californium-252, 71.11&nbsp;MeV. That last is the largest of the four chains, unsurprisingly for the shell-stability of the product.

{| class="wikitable" style="margin:auto; text-align:center;"
!rowspan=2|Nuclide
!colspan=2|Historic names
!rowspan=2|Decay mode
!rowspan=2|Half-life<br />(''a'' = years)
!rowspan=2|Energy released<br/>MeV
!rowspan=2|Decay<br/>product
|-
!Short!!Long
|-
| [[Californium-252|<sup>252</sup>Cf]]
| 
| 
| [[alpha decay|α]]
| 2.645 a
| 6.217
| [[Curium-248|<sup>248</sup>Cm]]
|-
| [[Curium-248|<sup>248</sup>Cm]]
| 
| 
| α
| 3.48{{e|5}} a
| 5.162
| [[Plutonium-244|<sup>244</sup>Pu]]
|-
| [[Plutonium-244|<sup>244</sup>Pu]]
|
|
| α
| 8.13{{e|7}} a
| 4.666
| [[Uranium-240|<sup>240</sup>U]]
|-
| [[Uranium-240|<sup>240</sup>U]]
| 
| 
| [[beta decay|β<sup>−</sup>]]
| 14.1 h
| 0.382
| [[Neptunium-240m|<sup>240m</sup>Np]]<ref name="isomer">ENSDF analysis available at {{NNDC}}</ref>
|-
| [[Neptunium-240m|<sup>240m</sup>Np]]
| 
| 
| [[Isomeric transition|IT]] 0.12%<br /> β<sup>−</sup> 99.88%
| 7.22 min
| 0.018<br />2.209
| [[Neptunium-240|<sup>240</sup>Np]]<br />[[Plutonium-240|<sup>240</sup>Pu]]
|-
| [[Neptunium-240|<sup>240</sup>Np]]
| 
| 
| β<sup>−</sup>
| 61.9 min
| 2.191
| [[Plutonium-240|<sup>240</sup>Pu]]
|-
| [[Plutonium-240|<sup>240</sup>Pu]]
| 
| 
| α
| 6561 a
| 5.256
| [[Uranium-236|<sup>236</sup>U]]
|-
| [[Uranium-236|<sup>236</sup>U]]
| 
| Thoruranium<ref name=thoruranium>{{cite journal |last1=Trenn |first1=Thaddeus J. |date=1978 |title=Thoruranium (U-236) as the extinct natural parent of thorium: The premature falsification of an essentially correct theory |journal=Annals of Science |volume=35 |issue=6 |pages=581–97 |doi=10.1080/00033797800200441}}</ref>
| α
| 2.342{{e|7}} a
| 4.573
| [[Thorium-232|<sup>232</sup>Th]]
|-
| [[Thorium-232|<sup>232</sup>Th]]
| Th
| Thorium
| α
| 1.40{{e|10}} a
| 4.082
| [[Radium-228|<sup>228</sup>Ra]]
|-
| [[Radium-228|<sup>228</sup>Ra]]
| MsTh<sub>1</sub>
| Mesothorium 1
| β<sup>−</sup>
| 5.75 a
| 0.046
| [[Actinium-228|<sup>228</sup>Ac]]
|-
| [[Actinium-228|<sup>228</sup>Ac]]
| MsTh<sub>2</sub>
| Mesothorium 2
| β<sup>−</sup>
| 6.15 h
| 2.123
| [[Thorium-228|<sup>228</sup>Th]]
|-
| [[Thorium-228|<sup>228</sup>Th]]
| RdTh
| Radiothorium
| α
| 1.9125 a
| 5.520
| [[Radium-224|<sup>224</sup>Ra]]
|-
| [[Radium-224|<sup>224</sup>Ra]]
| ThX
| Thorium X
| α
| 3.632 d
| 5.789
| [[Radon-220|<sup>220</sup>Rn]]
|-
| [[Radon-220|<sup>220</sup>Rn]]
| Tn
| Thoron,<br />Thorium Emanation
| α
| 55.6 s
| 6.405
| [[Polonium-216|<sup>216</sup>Po]]
|-
| [[Polonium-216|<sup>216</sup>Po]]
| ThA
| Thorium A
| α
| 0.144 s
| 6.906
| [[Lead-212|<sup>212</sup>Pb]]
|-
| [[Lead-212|<sup>212</sup>Pb]]
| ThB
| Thorium B
| β<sup>−</sup>
| 10.627 h
| 0.569
| [[Bismuth-212|<sup>212</sup>Bi]]
|-
| [[Bismuth-212|<sup>212</sup>Bi]]
| ThC
| Thorium C
| β<sup>−</sup> 64.06% <br /> α 35.94%
| 60.55 min
| 2.252 <br /> 6.207
| [[Polonium-212|<sup>212</sup>Po]] <br /> [[Thallium-208|<sup>208</sup>Tl]]
|-
| [[Polonium-212|<sup>212</sup>Po]]
| ThC′
| Thorium C′
| α
| 294.4 ns
| 8.954
| [[Lead-208|<sup>208</sup>Pb]]
|-
| [[Thallium-208|<sup>208</sup>Tl]]
| ThC″
| Thorium C″
| β<sup>−</sup>
| 3.053 min
| 4.999
| [[Lead-208|<sup>208</sup>Pb]]
|-
| [[Lead-208|<sup>208</sup>Pb]]
| ThD
| Thorium D
| stable
|
|
|
|}

===Neptunium series===
[[Image:Decay Chain(4n+1, Neptunium Series).svg|300px|thumb|right]]
The 4n+1 chain of neptunium-237 is commonly called the "neptunium series" or "neptunium cascade". In this series, only two of the isotopes involved are found naturally in significant quantities, namely the final two: bismuth-209 and thallium-205. Some of the other isotopes have been detected in nature, originating from trace quantities of <sup>237</sup>Np produced by the (n,2n) [[spallation|knockout]] reaction in primordial <sup>238</sup>U.<ref name=4n1>{{cite journal |last1=Peppard |first1=D. F. |last2=Mason |first2=G. W. |last3=Gray |first3=P. R. |last4=Mech |first4=J. F. |title=Occurrence of the (4n + 1) series in nature |journal=Journal of the American Chemical Society |date=1952 |volume=74 |issue=23 |pages=6081–6084 |doi=10.1021/ja01143a074 |bibcode=1952JAChS..74.6081P |url=https://digital.library.unt.edu/ark:/67531/metadc172698/m2/1/high_res_d/metadc172698.pdf }}</ref>

Since this series was only discovered and studied in 1947–1948,<ref name=th2>{{Thoennessen2016|pages=20}}</ref> its nuclides were never given historic names. Uniquely among the four, this decay chain has an isotope of radon only produced in a rare branch (not shown in the illustration) but not in the main decay sequence; thus, radon from this decay chain will hardly migrate through rock. Also uniquely, it ends in thallium (or, practically speaking, bismuth) rather than lead. This series terminates with the stable isotope thallium-205, 8 [[alpha decay]]s and 4 [[beta decay]]s from neptunium.

The total energy released from neptunium-237 to thallium-205, including the energy lost to [[neutrino]]s, is 49.29&nbsp;MeV; from californium-249, 66.87&nbsp;MeV. As the energy of the final step from bismuth to thallium, though known, will not be available until the inconceivable future, it may be better to quote the figures 46.16&nbsp;MeV and 63.73&nbsp;MeV to bismuth-209.

{| class="wikitable" style="margin:auto; text-align:center;"
!Nuclide
!Decay mode
!Half-life<br />(''a'' = years)
!Energy released<br/>MeV
!Decay product
|-
| [[Californium-249|<sup>249</sup>Cf]]
| [[alpha decay|α]]
| 351 a
| 6.293
| [[Curium-245|<sup>245</sup>Cm]]
|-
| [[Curium-245|<sup>245</sup>Cm]]
| α
| 8250 a
| 5.624
| [[Plutonium-241|<sup>241</sup>Pu]]
|-
| [[Plutonium-241|<sup>241</sup>Pu]]
| [[beta decay|β<sup>−</sup>]] 99.9975%<br /> α 0.0025%
| 14.33 a
| 0.021<br />5.140
| [[Americium-241|<sup>241</sup>Am]]<br />[[Uranium-237|<sup>237</sup>U]]
|-
| [[Americium-241|<sup>241</sup>Am]]
| α
| 432.6 a
| 5.638
| [[Neptunium-237|<sup>237</sup>Np]]
|-
| [[Uranium-237|<sup>237</sup>U]]
| β<sup>−</sup>
| 6.752 d
| 0.518
| [[Neptunium-237|<sup>237</sup>Np]]
|-
| [[Neptunium-237|<sup>237</sup>Np]]
| α
| 2.144×10<sup>6</sup> a
| 4.957
| [[Protactinium-233|<sup>233</sup>Pa]]
|-
| [[Protactinium-233|<sup>233</sup>Pa]]
| β<sup>−</sup>
| 26.98 d
| 0.570
| [[Uranium-233|<sup>233</sup>U]]
|-
| [[Uranium-233|<sup>233</sup>U]]
| α
| 1.592×10<sup>5</sup> a
| 4.909
| [[Thorium-229|<sup>229</sup>Th]]
|-
| [[Thorium-229|<sup>229</sup>Th]]
| α
| 7920 a
| 5.168
| [[Radium-225|<sup>225</sup>Ra]]
|-
| [[Radium-225|<sup>225</sup>Ra]]
| β<sup>−</sup> 99.9974%<br />α 0.0026%<ref>{{cite journal | last1=Liang | first1=C. F. | last2=Paris | first2=P. | last3=Sheline | first3=R. K. | title=α decay of <sup>225</sup>Ra | journal=Physical Review C | publisher=American Physical Society (APS) | volume=62 | issue=4 | date=2000-09-19 | article-number=047303 | issn=0556-2813 | doi=10.1103/physrevc.62.047303| bibcode=2000PhRvC..62d7303L }}</ref>{{efn|The value .026%, found at other places, is a typographical error. The original data is cited here.}}
| 14.8 d
| 0.356<br />5.097
| [[Actinium-225|<sup>225</sup>Ac]]<br />[[Radon-221|<sup>221</sup>Rn]]
|-
| [[Actinium-225|<sup>225</sup>Ac]]
| α
| 9.919 d
| 5.935
| [[Francium-221|<sup>221</sup>Fr]]
|-
| [[Radon-221|<sup>221</sup>Rn]]
| β<sup>−</sup> 78%<br />α 22%
| 25.7 min
| 1.194<br />6.163
| [[Francium-221|<sup>221</sup>Fr]]<br />[[Polonium-217|<sup>217</sup>Po]]
|-
| [[Francium-221|<sup>221</sup>Fr]]
| α 99.9952% <br /> β<sup>−</sup> 0.0048%
| 4.801 min
| 6.457<br /> 0.313
| [[Astatine-217|<sup>217</sup>At]]<br />[[Radium-221|<sup>221</sup>Ra]]
|-
| [[Radium-221|<sup>221</sup>Ra]]
| α
| 25 s
| 6.880
| [[Radon-217|<sup>217</sup>Rn]]
|-
| [[Polonium-217|<sup>217</sup>Po]]
| α 97.5% <br /> β<sup>−</sup> 2.5%
| 1.53 s
| 6.662<br />1.488
| [[Lead-213|<sup>213</sup>Pb]] <br /> [[Astatine-217|<sup>217</sup>At]]
|-
| [[Astatine-217|<sup>217</sup>At]]
| α 99.992% <br /> β<sup>−</sup> 0.008%
| 32.6 ms
| 7.202 <br /> 0.736
| [[Bismuth-213|<sup>213</sup>Bi]] <br /> [[Radon-217|<sup>217</sup>Rn]]
|-
| [[Radon-217|<sup>217</sup>Rn]]
| α
| 590 μs
| 7.888
| [[Polonium-213|<sup>213</sup>Po]]
|-
| [[Lead-213|<sup>213</sup>Pb]]
| β<sup>−</sup>
| 10.2 min
| 2.028
| [[Bismuth-213|<sup>213</sup>Bi]]
|-
| [[Bismuth-213|<sup>213</sup>Bi]]
| β<sup>−</sup> 97.91% <br /> α 2.09%
| 45.6 min
| 1.422 <br /> 5.988
| [[Polonium-213|<sup>213</sup>Po]] <br /> [[Thallium-209|<sup>209</sup>Tl]]
|-
| [[Polonium-213|<sup>213</sup>Po]]
| α
| 3.705 μs
| 8.536
| [[Lead|<sup>209</sup>Pb]]
|-
| [[Thallium-209|<sup>209</sup>Tl]]
| β<sup>−</sup>
| 2.162 min
| 3.970
| [[Lead-209|<sup>209</sup>Pb]]
|-
| [[Lead-209|<sup>209</sup>Pb]]
| β<sup>−</sup>
| 3.235 h
| 0.644
| [[Bismuth-209|<sup>209</sup>Bi]]
|-
| [[Bismuth-209|<sup>209</sup>Bi]]
| α
| 2.01×10<sup>19</sup> a
| 3.137
| [[Thallium-205|<sup>205</sup>Tl]]
|-
| [[Thallium-205|<sup>205</sup>Tl]]
| stable
|
|
|
|}
{{notelist}}

=== {{anchor|Radium series}} Uranium series ===
[[Image:Decay chain(4n+2, Uranium series).svg|thumb|right|350px|alt=Uranium series|[[commons:File:Uranium series.gif|(More comprehensive graphic)]]]]
The 4n+2 chain of uranium-238 is called the "uranium series" or "radium series", the latter from the first member known when it was named, radium-226. The series terminates with lead-206, 8 [[alpha decay]]s and 6 [[beta decay]]s from uranium.

The total energy released from uranium-238 to lead-206, including the energy lost to neutrinos, is 51.69&nbsp;MeV; from californium-250, 68.28&nbsp;MeV.

{| class="wikitable" style="margin:auto; text-align:center;"
!rowspan=2|Nuclide
!colspan=2|Historic names
!rowspan=2|Decay mode
!rowspan=2|Half-life<br />(''a'' = years)
!rowspan=2|Energy released<br/>MeV
!rowspan=2|Decay<br/>product
|-
!Short!!Long
|-
| [[Californium-250|<sup>250</sup>Cf]]
|
|
| [[alpha decay|α]]
| 13.08 a
| 6.128
| [[Curium-246|<sup>246</sup>Cm]]
|-
| [[Curium-246|<sup>246</sup>Cm]]
|
|
| α
| 4760 a
| 5.475
| [[Plutonium-242|<sup>242</sup>Pu]]
|-
| [[Plutonium-242|<sup>242</sup>Pu]]
|
|
| α
| 3.75×10<sup>5</sup> a
| 4.984
| [[Uranium-238|<sup>238</sup>U]]
|-
| [[Uranium-238|<sup>238</sup>U]]
| U<sub>I</sub>
| Uranium I
| α
| 4.463×10<sup>9</sup> a
| 4.270
| [[Thorium-234|<sup>234</sup>Th]]
|-
| [[Thorium-234|<sup>234</sup>Th]]
| UX<sub>1</sub>
| Uranium X<sub>1</sub>
| [[beta decay|β<sup>−</sup>]]
| 24.11 d
| 0.195
| [[Protactinium-234m|<sup>234m</sup>Pa]]<ref name="isomer" />
|-
| [[Protactinium-234m|<sup>234m</sup>Pa]]
| UX<sub>2</sub>, Bv
| Uranium X<sub>2</sub><br/>Brevium
| [[Isomeric transition|IT]] 0.16%<br /> β<sup>−</sup> 99.84%
| 1.16 min
| 0.079<br />2.273
| [[Protactinium-234|<sup>234</sup>Pa]]<br />[[Uranium-234|<sup>234</sup>U]]
|-
| [[Protactinium-234|<sup>234</sup>Pa]]
| UZ
| Uranium Z
| β<sup>−</sup>
| 6.70 h
| 2.194
| [[Uranium-234|<sup>234</sup>U]]
|-
| [[Uranium-234|<sup>234</sup>U]]
| U<sub>II</sub>
| Uranium II
| α
| 2.455×10<sup>5</sup> a
| 4.858
| [[Thorium-230|<sup>230</sup>Th]]
|-
| [[Thorium-230|<sup>230</sup>Th]]
| Io
| Ionium
| α
| 7.54×10<sup>4</sup> a
| 4.770
| [[Radium-226|<sup>226</sup>Ra]]
|-
| [[Radium-226|<sup>226</sup>Ra]]
| Ra
| Radium
| [[alpha decay|α]]
| 1600 a
| 4.871
| [[Radon-222|<sup>222</sup>Rn]]
|-
| [[Radon-222|<sup>222</sup>Rn]]
| Rn
|  Radon,<br/>Radium Emanation
| α
| 3.8215 d
| 5.590
| [[Polonium-218|<sup>218</sup>Po]]
|-
| [[Polonium-218|<sup>218</sup>Po]]
| RaA
| Radium A
| α 99.98%<br /> β<sup>−</sup> 0.02%
| 3.097 min
| 6.115<br />0.257
| [[Lead-214|<sup>214</sup>Pb]]<br />[[Astatine-218|<sup>218</sup>At]]
|-
| [[Astatine-218|<sup>218</sup>At]]
| 
| 
| α 100%<br /> β<sup>−</sup>
| 1.28 s
| 6.876<br />2.883
| [[Bismuth-214|<sup>214</sup>Bi]]<br />[[Radon-218|<sup>218</sup>Rn]]
|-
| [[Radon-218|<sup>218</sup>Rn]]
| 
| 
| α
| 33.75 ms
| 7.262
| [[Polonium-214|<sup>214</sup>Po]]
|-
| [[Lead-214|<sup>214</sup>Pb]]
| RaB
| Radium B
| β<sup>−</sup>
| 27.06 min
| 1.018
| [[Bismuth-214|<sup>214</sup>Bi]]
|-
| [[Bismuth-214|<sup>214</sup>Bi]]
| RaC	
| Radium C
| β<sup>−</sup> 99.979%<br /> α 0.021%
| 19.9 min
| 3.269<br />5.621
| [[Polonium-214|<sup>214</sup>Po]]<br />[[Thallium-210|<sup>210</sup>Tl]]
|-
| [[Polonium-214|<sup>214</sup>Po]]
| RaC'
| Radium C'
| α
| 163.5 μs
| 7.833
| [[Lead-210|<sup>210</sup>Pb]]
|-
| [[Thallium-210|<sup>210</sup>Tl]]
| RaC"
| Radium C"
| β<sup>−</sup><br />[[Beta-delayed neutron emission|β<sup>−</sup>n]] 0.009%
| 1.30 min
| 5.481<br />0.296
| [[Lead-210|<sup>210</sup>Pb]]<br />[[Lead-209|<sup>209</sup>Pb]] (in [[neptunium series]])
|-
| [[Lead-210|<sup>210</sup>Pb]]
| RaD
| Radium D
| β<sup>−</sup><br /> α 1.9×10<sup>−6</sup>%
| 22.2 a
| 0.0635<br />3.793
| [[Bismuth-210|<sup>210</sup>Bi]]<br />[[Mercury-206|<sup>206</sup>Hg]]
|-
| [[Bismuth-210|<sup>210</sup>Bi]]
| RaE
| Radium E	
| β<sup>−</sup><br /> α 1.32×10<sup>−4</sup>%
| 5.012 d
| 1.161<br />5.035
| [[Polonium-210|<sup>210</sup>Po]]<br />[[Thallium-206|<sup>206</sup>Tl]]
|-
| [[Polonium-210|<sup>210</sup>Po]]
| RaF
| Radium F
| α
| 138.376 d
| 5.407
| [[Lead-206|<sup>206</sup>Pb]]
|-
| [[Mercury-206|<sup>206</sup>Hg]]
| 
| 
| β<sup>−</sup>
| 8.32 min
| 1.307
| [[Thallium-206|<sup>206</sup>Tl]]
|-
| [[Thallium-206|<sup>206</sup>Tl]]
| RaE"
| Radium E"
| β<sup>−</sup>
| 4.20 min
| 1.532
| [[Lead-206|<sup>206</sup>Pb]]
|-
| [[Lead-206|<sup>206</sup>Pb]]
| RaG
| Radium G
| stable
|
|
|
|}
{{notelist}}

=== Actinium series ===
[[Image:Decay Chain of Actinium.svg|thumb|right|300px|alt=Actinium series|([[commons:File:Decay scheme U235.png|More detailed graphic]])]]
The 4n+3 chain of [[uranium-235]] is commonly called the "actinium series" or "actinium cascade", from the first member known when it was named, actinium-227. This series terminates with lead-207, 7 [[alpha decay]]s and 4 [[beta decay]]s from uranium.

In the early Solar System, this chain went back to <sup>247</sup>Cm. This manifests itself today as variations in <sup>235</sup>U/<sup>238</sup>U ratios, since [[curium]] and uranium have noticeably different chemistries and therefore partitioned differently.<ref name=Davis/><ref>{{cite journal |last1=Tsaletka |first1=R. |last2=Lapitskii |first2=A. V. |date=1960 |title=Occurrence of the Transuranium Elements in Nature |url=https://www.russchemrev.org/RCR1264pdf |journal=Russian Chemical Reviews |volume=29 |issue=12 |pages=684–689 |doi= 10.1070/RC1960v029n12ABEH001264|bibcode=1960RuCRv..29..684T |access-date=20 January 2024}}</ref>

The total energy released from uranium-235 to lead-207, including the energy lost to neutrinos, is 46.40&nbsp;MeV; from californium-251, 69.91&nbsp;MeV.

{| class="wikitable" style="margin:auto; text-align:center;"
!rowspan=2|Nuclide
!colspan=2|Historic name
!rowspan=2|Decay mode
!rowspan=2|Half-life<br />(''a'' = years)
!rowspan=2|Energy released<br/>MeV
!rowspan=2|Decay<br/>product
|-
!Short!!Long
|-
| [[Californium-251|<sup>251</sup>Cf]]
| 
| 
| [[alpha decay|α]]
| 900&nbsp;a
| 6.177
| [[Curium-247|<sup>247</sup>Cm]]
|-
| [[Curium-247|<sup>247</sup>Cm]]
|
|
| α
| 1.56×10<sup>7</sup> a
| 5.353
| [[Plutonium-243|<sup>243</sup>Pu]]
|-
| [[Plutonium-243|<sup>243</sup>Pu]]
|
| 
| [[beta decay|β<sup>&minus;</sup>]]
| 4.955&nbsp;h
| 0.578
| [[Americium-243|<sup>243</sup>Am]]
|-
| [[Americium-243|<sup>243</sup>Am]]
| 
| 
| α
| 7350&nbsp;a
| 5.439
| [[Neptunium-239|<sup>239</sup>Np]]
|-
| [[Neptunium-239|<sup>239</sup>Np]]
| 
| 
| β<sup>-</sup>
| 2.356&nbsp;d
| 0.723
| [[Plutonium-239|<sup>239</sup>Pu]]
|-
| [[Plutonium-239|<sup>239</sup>Pu]]
| 
| 
| α
| 2.411×10<sup>4</sup> a
| 5.244
| [[Uranium-235|<sup>235</sup>U]]
|-
| [[Uranium-235|<sup>235</sup>U]]
| AcU
| Actino-uranium
| α
| 7.04×10<sup>8</sup> a
| 4.678
| [[Thorium-231|<sup>231</sup>Th]]
|-
| [[Thorium-231|<sup>231</sup>Th]]
| UY
| Uranium Y
| β<sup>−</sup>
| 25.52 h
| 0.391
| [[Protactinium-231|<sup>231</sup>Pa]]
|-
| [[Protactinium-231|<sup>231</sup>Pa]]
| Pa
| Protoactinium
| α
| 3.27×10<sup>4</sup> a
| 5.150
| [[Actinium-227|<sup>227</sup>Ac]]
|-
| [[Actinium-227|<sup>227</sup>Ac]]
| Ac
| Actinium
| β<sup>−</sup> 98.62%<br /> α 1.38%
| 21.772 a
| 0.045<br />5.042
| [[Thorium-227|<sup>227</sup>Th]]<br />[[Francium-223|<sup>223</sup>Fr]]
|-
| [[Thorium-227|<sup>227</sup>Th]]
| RdAc
| Radioactinium
| α
| 18.693 d
| 6.147
| [[Radium-223|<sup>223</sup>Ra]]
|-
| [[Francium-223|<sup>223</sup>Fr]]
| AcK
| Actinium K
| β<sup>−</sup> 99.994%<br /> α 0.006%
| 22.00 min
| 1.149<br />5.561
| [[Radium-223|<sup>223</sup>Ra]]<br />[[Astatine-219|<sup>219</sup>At]]
|-
| [[Radium-223|<sup>223</sup>Ra]]
| AcX
| Actinium X
| α
| 11.435 d
| 5.979
| [[Radon-219|<sup>219</sup>Rn]]
|-
| [[Astatine-219|<sup>219</sup>At]]
|
|
| α 93.6%<br /> β<sup>−</sup> 6.4%
| 56 s
| 6.342<br />1.567
| [[Bismuth-215|<sup>215</sup>Bi]]<br />[[Radon-219|<sup>219</sup>Rn]]
|-
| [[Radon-219|<sup>219</sup>Rn]]
| An
| Actinon,<br />Actinium Emanation
| α
| 3.96 s
| 6.946
| [[Polonium-215|<sup>215</sup>Po]]
|-
| [[Bismuth-215|<sup>215</sup>Bi]]
|
|
| β<sup>−</sup>
| 7.6 min
| 2.171  	
| [[Polonium-215|<sup>215</sup>Po]]
|-
| [[Polonium-215|<sup>215</sup>Po]]
| AcA
| Actinium A
| α<br /> β<sup>−</sup> 2.3×10<sup>−4</sup>%
| 1.781 ms
| 7.526 <br /> 0.715
| [[Lead-211|<sup>211</sup>Pb]] <br /> [[Astatine-215|<sup>215</sup>At]]
|-
| [[Astatine-215|<sup>215</sup>At]]
|
|
| α
| 37 μs
| 8.177
| [[Bismuth-211|<sup>211</sup>Bi]]
|-
| [[Lead-211|<sup>211</sup>Pb]]
| AcB
| Actinium B
| β<sup>−</sup>
| 36.16 min
| 1.366
| [[Bismuth-211|<sup>211</sup>Bi]]
|-
| [[Bismuth-211|<sup>211</sup>Bi]]
| AcC
| Actinium C
| α 99.724%<br /> β<sup>−</sup> 0.276%
| 2.14 min
| 6.750<br />0.573
| [[Thallium-207|<sup>207</sup>Tl]]<br />[[Polonium-211|<sup>211</sup>Po]]
|-
| [[Polonium-211|<sup>211</sup>Po]]
| AcC'
| Actinium C'
| α
| 516 ms
| 7.595
| [[Lead-207|<sup>207</sup>Pb]]
|-
| [[Thallium-207|<sup>207</sup>Tl]]
| AcC"
| Actinium C"
| β<sup>−</sup>
| 4.77 min
| 1.418
| [[Lead-207|<sup>207</sup>Pb]]
|-
| [[Lead-207|<sup>207</sup>Pb]]
| AcD
| Actinium D
| stable
|
|
|
|}

== See also ==
* [[Nuclear physics]]
* [[Radioactive decay]]
* [[Valley of stability]]
* [[Decay product]]
* [[Radioisotopes]] ([[radionuclide]])
* [[Radiometric dating]]

== Notes ==
{{reflist}}

== References ==
* {{cite book
 |author1=C.M. Lederer |author2=J.M. Hollander |author3=I. Perlman |year=1968
 |title=Table of Isotopes
 |edition=6th
 |location=New York
 |publisher=[[John Wiley & Sons]]
}}

== External links ==
{{commons category|Decay chain}}
* [http://www.nucleonica.com Nucleonica nuclear science portal]
* [http://www.nucleonica.com/wiki/index.php?title=Help%3ADecay_Engine Nucleonica's Decay Engine for professional online decay calculations]
* [https://www.epa.gov/radiation/radioactive-decay EPA – Radioactive Decay]
* [https://web.archive.org/web/20061205022425/http://ie.lbl.gov/education/isotopes.htm Government website listing isotopes and decay energies]
* [http://www.nndc.bnl.gov National Nuclear Data Center] – freely available databases that can be used to check or construct decay chains
* [[Image:Ndslivechart.png]] [http://www-nds.iaea.org/livechart IAEA – Live Chart of Nuclides] (with decay chains)
* [http://www.wolframalpha.com/widgets/gallery/view.jsp?id=23174474f31785ce939641039a212de4 Decay Chain Finder]

[[Category:Radioactivity]]