Editing Radioactive decay (section)

{{short description|Emissions from unstable atomic nuclei}}
{{Redirect2|Radioactive|Radioactivity|other uses|Radioactive (disambiguation)|and|Radioactivity (disambiguation)}}
{{for-multi|particle decay in a more general context|Particle decay|more information on hazards of various kinds of radiation from decay|Ionizing radiation}}
{{Use British English|date=May 2014}}
{{Use dmy dates|date=May 2014}}
[[File:Alpha Decay.svg|thumb|[[Alpha decay]] by a nucleus emits an [[alpha particle]] of two neutrons and two protons; also known as a [[helium|helium-4]] nucleus.|300x300px]]{{Nuclear physics}}'''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 considered ''radioactive''. Three of the most common types of decay are [[Alpha decay|alpha]], [[Beta decay|beta]], and [[Gamma ray|gamma decay]]. The [[weak force]] is the [[Fundamental interactions|mechanism]] that is responsible for beta decay, while the other two are governed by the [[electromagnetic force|electromagnetic]] and [[nuclear force]]s.<ref name="edp">{{cite web |title=Radioactivity: Weak Forces |url=https://www.radioactivity.eu.com/site/pages/Weak_Forces.htm |website=Radioactivity |publisher=EDP Sciences |access-date=4 March 2020 |archive-date=12 August 2021 |archive-url=https://web.archive.org/web/20210812235150/https://www.radioactivity.eu.com/site/pages/Weak_Forces.htm |url-status=dead }}</ref>

Radioactive decay is a [[randomness|random]] process at the level of single atoms. According to [[quantum mechanics|quantum theory]], it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed.<ref name="IntroductionToHealthPhysics">{{cite book |title=Radiation Protection and Dosimetry: An Introduction to Health Physics |last1=Stabin |first1=Michael G. |editor1-first=Michael G |editor1-last=Stabin |isbn=978-0-387-49982-6 |year=2007 |publisher=[[Springer Publishing|Springer]] |chapter=3 |doi=10.1007/978-0-387-49983-3|chapter-url=https://cds.cern.ch/record/1105894 }}</ref><ref name="RadiationOncologyPrimer">{{cite book |title=Radiation Oncology Primer and Review |isbn=978-1-62070-004-4 |last1=Best |first1=Lara |last2=Rodrigues |first2=George |last3=Velker |first3=Vikram |publisher=[[Demos Medical Publishing]] |year=2013 |chapter=1.3}}</ref><ref>{{cite book |title=Modern Nuclear Chemistry |isbn=978-0-471-11532-8 |last1=Loveland |first1=W. |last2=Morrissey |first2=D. |author3-link=Glenn T. Seaborg |last3=Seaborg |first3=G.T. |publisher=Wiley-Interscience |year=2006 |page=57|bibcode=2005mnc..book.....L }}</ref> However, for a significant number of identical atoms, the overall decay rate can be expressed as a [[decay constant]] or as a [[half-life]]. The half-lives of radioactive atoms have a huge range: from nearly instantaneous to far longer than the [[age of the universe]].

The decaying nucleus is called the parent [[radionuclide]] (or parent [[Isotope#Isotope vs. nuclide|radioisotope]]), and the process produces at least one [[Decay product|daughter nuclide]]. Except for gamma decay or [[internal conversion]] from a nuclear [[excited state]], the decay is a [[nuclear transmutation]] resulting in a daughter containing a different number of [[proton]]s or [[neutron]]s (or both). When the number of protons changes, an atom of a different [[chemical element]] is created.

There are 28 naturally occurring chemical elements on Earth that are radioactive, consisting of 35 [[radionuclide]]s (seven elements have two different radionuclides each) that date before the time of formation of the [[Solar System]]. These 35 are known as [[primordial radionuclide]]s. Well-known examples are [[uranium]] and [[thorium]], but also included are naturally occurring long-lived radioisotopes, such as [[potassium-40]]. Each of the heavy [[Primordial nuclide|primordial radionuclides]] participates in one of the four [[decay chain]]s.