Editing Nucleocosmochronology (section)

{{short description|Technique to determine timescales for astrophysical objects and events}}
{{Expert needed|physics
| date = August 2024
| ex2 = astronomy
| reason = The subject is very technical and needs a clear and correct explanation of how the technique works
}}

'''Nucleocosmochronology''', or '''nuclear cosmochronology''', is a technique used to determine timescales for [[astrophysics|astrophysical]] objects and events based on observed ratios of radioactive heavy elements and their decay products. It is similar in many respects to [[radiometric dating]], in which trace radioactive [[impurity|impurities]] were selectively incorporated into materials when they were formed.

To calculate the age of formation of astronomical objects, the observed ratios of [[Abundance of the chemical elements|abundances]] of heavy [[radionuclide|radioactive]] and [[stable nuclide]]s are compared to the primordial ratios predicted by [[Nucleosynthesis|nucleosynthesis theory]].<ref name="Bland-Hawthorn Freeman 2014 pp. 1–144">{{cite book | last1=Bland-Hawthorn | first1=Joss | last2=Freeman | first2=Kenneth | series=Saas-Fee Advanced Course | volume=37 | title=The Origin of the Galaxy and Local Group | chapter=Near Field Cosmology: The Origin of the Galaxy and the Local Group | publisher=Springer Berlin Heidelberg | publication-place=Berlin, Heidelberg | year=2014 | isbn=978-3-642-41719-1 | issn=1861-7980 | doi=10.1007/978-3-642-41720-7_1 | pages=1–144| bibcode=2014SAAS...37....1B }}</ref> Both radioactive elements and their decay products matter, and some important elements include the long-lived radioactive nuclei [[Th-232]], [[Uranium-235|U-235]], and [[Uranium-238|U-238]], all formed by the [[r-process]].<ref name=":0">{{Cite journal |last1=Meyer |first1=Bradley S |last2=Truran |first2=James W |date=2000-08-01 |title=Nucleocosmochronology |url=https://www.sciencedirect.com/science/article/abs/pii/S0370157300000120 |journal=Physics Reports |volume=333-334 |pages=1–11 |doi=10.1016/S0370-1573(00)00012-0 |bibcode=2000PhR...333....1M |issn=0370-1573}}</ref> The process has been compared to [[radiocarbon dating]].<ref name=":0" /><ref name=":1">{{Cite journal |last1=Symbalisty |first1=E M D |last2=Schramm |first2=D N |date=1981-03-01 |title=Nucleocosmochronology |url=https://iopscience.iop.org/article/10.1088/0034-4885/44/3/002 |journal=Reports on Progress in Physics |volume=44 |issue=3 |pages=293–328 |doi=10.1088/0034-4885/44/3/002 |issn=0034-4885}}</ref> The age of the objects are determined by placing constraints on the duration of nucleosynthesis in the galaxy.<ref name=":0" />

Nucleocosmochronology has been employed to determine the age of the [[Sun]] ({{val|4.57|0.02}} billion years) and of the Galactic [[thin disk]] ({{val|8.8|1.8}} billion years),<ref>{{Cite journal |last1=del Peloso |first1=E. F. |last2=da Silva |first2=L. |last3=de Mello |first3=G. F. Porto |date=April 2005 |title=The age of the Galactic thin disk from Th/Eu nucleocosmochronology I. Determination of [Th/Eu] abundance ratios |journal=Astronomy & Astrophysics |volume=434 |issue=1 |pages=275–300 |doi=10.1051/0004-6361:20047060 |issn=0004-6361|arxiv=astro-ph/0411698 |bibcode=2005A&A...434..275D }}</ref><ref>{{Cite journal |last1=del Peloso |first1=E. F. |last2=da Silva |first2=L. |last3=Arany-Prado |first3=L. I. |date=April 2004 |title=The age of the Galactic thin disk from Th/Eu nucleocosmochronology II. Chronological analysis |journal=Astronomy & Astrophysics |volume=434 |issue=1 |pages=301–308 |doi=10.1051/0004-6361:20042438 |issn=0004-6361|arxiv=astro-ph/0411699 }}</ref><ref>{{Cite journal |last1=del Peloso |first1=E. F. |last2=da Silva |first2=L. |last3=de Mello |first3=G. F. Porto |last4=Arany-Prado |first4=L. I. |date=September 2005 |title=The age of the Galactic thin disk from Th/Eu nucleocosmochronology III. Extended sample |journal=Astronomy & Astrophysics |volume=440 |issue=3 |pages=1153–1159 |doi=10.1051/0004-6361:20053307 |issn=0004-6361|arxiv=astro-ph/0506458 |bibcode=2005A&A...440.1153D }}</ref> among other objects. It has also been used to estimate the age of the [[Milky Way]] itself by studying [[Cayrel's Star]] in the [[Galactic halo]], which due to its low [[metallicity]], is believed to have formed early in the history of the Galaxy.<ref name="Hill Plez Cayrel Beers 2002 pp. 560–579">{{cite journal | last1=Hill | first1=V. | last2=Plez | first2=B. | last3=Cayrel | first3=R. | last4=Beers | first4=T. C. | last5=Nordström | first5=B. | last6=Andersen | first6=J. | last7=Spite | first7=M. | last8=Spite | first8=F. | last9=Barbuy | first9=B. | last10=Bonifacio | first10=P. | last11=Depagne | first11=E. | last12=François | first12=P. | last13=Primas | first13=F.|author13-link=Francesca Primas | title=First stars. I. The extreme r-element rich, iron-poor halo giant CS 31082-001 | journal=Astronomy & Astrophysics | volume=387 | issue=2 | year=2002 | issn=0004-6361 | doi=10.1051/0004-6361:20020434 | pages=560–579| arxiv=astro-ph/0203462 | bibcode=2002A&A...387..560H | s2cid=3064681 | url=http://lup.lub.lu.se/record/118533 }}</ref>

Limiting factors in its precision are the quality of observations of faint stars and the uncertainty of the primordial abundances of [[r-process]] elements.{{Citation needed|date=August 2024}}