Editing Nuclide

{{Short description|Atomic species}}
{{Nuclear physics}}
'''Nuclides''' (or '''nucleides''', from [[atomic nucleus|nucleus]], also known as nuclear species) are a class of atoms characterized by their number of [[proton]]s, ''Z'', their number of [[neutron]]s, ''N'', and their nuclear [[energy state]].<ref>{{cite book|author=IUPAC|editor1=A. D. McNaught |editor2=A. Wilkinson|year=1997|chapter=Nuclide|chapter-url=http://goldbook.iupac.org/terms/view/N04257|title=Compendium of Chemical Terminology|publisher=[[Blackwell Scientific Publications]]|doi=10.1351/goldbook.N04257|isbn=978-0-632-01765-2|title-link=Compendium of Chemical Terminology|author-link=IUPAC}}</ref>

The word ''nuclide'' was coined by the American nuclear physicist [[Truman Paul Kohman|Truman P. Kohman]] in 1947.<ref>{{cite journal |title=Proposed New Word: ''Nuclide'' |last=Kohman |first=Truman P. |date=1947 |volume=15 |issue=4 |pages=356–7 |journal=American Journal of Physics |doi=10.1119/1.1990965 |bibcode=1947AmJPh..15..356K}}</ref><ref>{{cite news |url=http://old.post-gazette.com/pg/10121/1054684-122.stm |title=Obituary: Truman P. Kohman / Chemistry professor with eyes always on stars |last=Belko |first=Mark |date=1 May 2010 |newspaper=Pittsburgh Post-Gazette |access-date=29 April 2018 |archive-date=14 December 2019 |archive-url=https://web.archive.org/web/20191214003214/http://old.post-gazette.com/pg/10121/1054684-122.stm |url-status=dead }}</ref> Kohman defined ''nuclide'' as a "species of atom characterized by the constitution of its nucleus" containing a certain number of neutrons and protons. The term thus originally focused on the nucleus.

==Nuclides vs isotopes==
A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example carbon-13 with 6 protons and 7 neutrons. The nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, while the [[isotope]] concept (grouping all atoms of each element) emphasizes chemical over nuclear. The [[neutron]] number has large effects on nuclear properties, but its [[kinetic isotope effect|effect on chemical reactions]] is negligible for most elements. Even in the case of the very lightest elements, where the ratio of neutron number to atomic number varies the most between isotopes, it usually has only a small effect, but it matters in some circumstances. For hydrogen, the lightest element, the isotope effect is large enough to affect biological systems strongly. In the case of helium, [[helium-4]] obeys [[Bose–Einstein statistics]], while [[helium-3]] obeys [[Fermi–Dirac statistics]]. Since ''isotope'' is the older term, it is better known than ''nuclide'', and is still occasionally used in contexts in which ''nuclide'' might be more appropriate, such as nuclear technology and nuclear medicine.

==Types of nuclides==
<!--[[File:Island_of_Stability.svg|thumb|right|500px|Stability of nuclides]]-->
Although the words nuclide and isotope are often used interchangeably, being isotopes is actually only one relation between nuclides. The following table names some other relations.
<!-- This table conflicts with the sidebar in narrow windows. HTML experts, please fix it. -->
{| class="wikitable" style="float:left; margin:0em 0em 0em 1em;"
!Designation
!Characteristics
!Example
!Remarks
|- style="height:2em;"
|[[Isotope]]s
|equal proton number ([[atomic number|Z]]<sub>1</sub> = Z<sub>2</sub>)
|{{nuclide|link=yes|Carbon|12}}, {{nuclide|link=yes|Carbon|13}}, {{nuclide|link=yes|Carbon|14}}
| see [[neutron capture]]

|- style="height:2em;"
|[[Isotone]]s
|equal neutron number ([[neutron number|N]]<sub>1</sub> = N<sub>2</sub>)
|{{nuclide|link=yes|Carbon|13}}, {{nuclide|link=yes|Nitrogen|14}}, {{nuclide|link=yes|Oxygen|15}}
| see [[proton capture]]

|- style="height:2em;"
|[[Isobar (nuclide)|Isobars]]
|equal mass number (Z<sub>1</sub> + N<sub>1</sub> = Z<sub>2</sub> + N<sub>2</sub>)
|{{nuclide|link=yes|Nitrogen|17}}, {{nuclide|link=yes|Oxygen|17}}, {{nuclide|link=yes|Fluorine|17}}
|see [[beta decay]]
|- style="height:2em;"
|Isodiaphers
|equal neutron excess (N<sub>1</sub> − Z<sub>1</sub> = N<sub>2</sub> − Z<sub>2</sub>)
|{{nuclide|link=yes|Carbon|13}}, {{nuclide|link=yes|Nitrogen|15}}, {{nuclide|link=yes|Oxygen|17}}
|Examples are isodiaphers with neutron excess 1.<br/>
A nuclide and its [[alpha decay]] product are isodiaphers.<ref name=sharma/>
|- style="height:2em;"
|[[Mirror nuclei]]
|neutron and proton number exchanged<br/>
(Z<sub>1</sub> = N<sub>2</sub> ''and'' Z<sub>2</sub> = N<sub>1</sub>)
| style="text-align: center;" |{{nuclide|link=yes|Hydrogen|3}}, {{nuclide|link=yes|Helium|3}}
| see [[positron emission]]

|- style="height:2em;"
|[[Nuclear isomer]]s
|same proton number ''and'' mass number,<br/>
but with different energy states
| style="text-align: center;" |{{nuclide|link=yes|Technetium|99}}, {{nuclide|link=yes|Technetium|99m}}
|m=metastable (long-lived excited state)
|}
{{Clear|left}}

A set of nuclides with equal proton number ([[atomic number]]), i.e., of the same [[chemical element]] but different [[neutron number]]s, are called [[isotope]]s of the element. Particular nuclides are still often loosely called "isotopes", but the term "nuclide" is the correct one in general (i.e., when ''Z'' is not fixed). In similar manner, a set of nuclides with equal [[mass number]] ''A'', but different [[atomic number]], are called [[isobar (nuclide)|isobars]] (isobar = equal in weight), and [[isotone]]s are nuclides of equal neutron number but different proton numbers. Likewise, nuclides with the same neutron excess (''N''&nbsp;−&nbsp;''Z'') are called isodiaphers.<ref name=sharma>{{cite book|last=Sharma|first=B.K.|title=Nuclear and Radiation Chemistry|date=2001 |edition=7th|publisher=Krishna Prakashan Media|isbn=978-81-85842-63-9|page=78}}</ref> The name isoto'''n'''e was derived from the name isoto'''p'''e to emphasize that in the first group of nuclides it is the number of neutrons (n) that is constant, whereas in the second the number of protons (p).<ref>
{{cite journal
|last=Cohen |first=E. R.
|last2=Giacomo |first2=P.
|year=1987
|title=Symbols, units, nomenclature and fundamental constants in physics
|journal=[[Physica A]]
|volume=146 |issue=1 |pages=1–68
|bibcode=1987PhyA..146....1.
|citeseerx=10.1.1.1012.880
|doi=10.1016/0378-4371(87)90216-0
}}</ref>

See [[Isotope#Notation]] for an explanation of the notation used for different nuclide or isotope types.

[[Nuclear isomer]]s are members of a set of nuclides with equal proton number and equal mass number (thus making them by definition the same isotope), but different states of excitation. An example is the two states of the single isotope {{nuclide|link=yes|Technetium|99}} shown among the [[decay scheme]]s. Each of these two states (technetium-99m and technetium-99) qualifies as a different nuclide, illustrating one way that nuclides may differ from isotopes (an isotope may consist of several different nuclides of different excitation states).

The longest-lived non-[[ground state]] nuclear isomer is the nuclide [[tantalum-180m]] ({{nuclide|link=yes|Tantalum|180m}}), which has a [[half-life]] in excess of 1,000&nbsp;trillion years. This nuclide occurs primordially, and has never been observed to decay to the ground state. (In contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8&nbsp;hours to <sup>180</sup>Hf (86%) or <sup>180</sup>W (14%).)

There are 251&nbsp;nuclides in nature that have never been observed to decay. They occur among the 80 different elements that have one or more stable isotopes. See [[stable nuclide]] and [[primordial nuclide]]. Unstable nuclides are [[radioactivity|radioactive]] and are called [[radionuclide]]s. Their [[decay product]]s ('daughter' products) are called [[radiogenic nuclide]]s.

==Origins of naturally occurring radionuclides==
<!-- [[Primordial nuclide| No. there exist also radiogenic ones which are not primordial -->Natural radionuclides may be conveniently subdivided into three types.<ref name="SAHRA">{{cite web|title=Types of Isotopes: Radioactive|url=http://web.sahra.arizona.edu/programs/isotopes/types/radioactive.html|publisher=SAHRA|access-date=12 November 2016|archive-date=17 October 2021|archive-url=https://web.archive.org/web/20211017180747/http://web.sahra.arizona.edu/programs/isotopes/types/radioactive.html|url-status=dead}}</ref> First, those whose [[half-life|half-lives]] t<sub>1/2</sub> are at least 2% as long as the age of the [[Earth]] (for practical purposes, these are difficult to detect with half-lives less than 10% of the age of the Earth) ({{val|4.6|e=9|u=years}}). These are remnants of [[nucleosynthesis]] that occurred in stars before the formation of the [[Solar System]]. For example, the isotope {{SimpleNuclide|uranium|238}} (t<sub>1/2</sub> = {{val|4.5|e=9|u=years}}) of [[uranium]] is still fairly abundant in nature, but the shorter-lived isotope {{SimpleNuclide|uranium|235}} (t<sub>1/2</sub> = {{val|0.7|e=9|u=years}}) is 138 times rarer. About 34 of these nuclides have been discovered (see [[List of nuclides]] and [[Primordial nuclide]] for details).

The second group of radionuclides that exist naturally consists of [[radiogenic nuclide]]s such as {{SimpleNuclide|radium|226}} (t<sub>1/2</sub> = {{val|1602|u=years}}), an isotope of [[radium]], which are formed by [[radioactive decay]]. They occur in the decay chains of primordial isotopes of uranium or thorium. Some of these nuclides are very short-lived, such as [[isotopes of francium]]. There exist about 51 of these daughter nuclides that have half-lives too short to be primordial, and which exist in nature solely due to decay from longer lived radioactive primordial nuclides.

The third group consists of nuclides that are continuously being made in another fashion that is not simple spontaneous [[radioactive decay]] (i.e., only one atom involved with no incoming particle) but instead involves a natural [[nuclear reaction]]. These occur when atoms react with natural neutrons (from cosmic rays, [[spontaneous fission]], or other sources), or are bombarded directly with [[cosmic ray]]s. The latter, if non-primordial, are called [[cosmogenic nuclide]]s. Other types of natural nuclear reactions produce nuclides that are said to be [[nucleogenic]] nuclides.

An example of nuclides made by nuclear reactions, are cosmogenic {{SimpleNuclide|carbon|14}} ([[radiocarbon]]) that is made by [[cosmic ray]] bombardment of other elements, and nucleogenic {{SimpleNuclide|plutonium|239}} which is still being created by neutron bombardment of natural {{SimpleNuclide|uranium|238}} as a result of natural fission in uranium ores. Cosmogenic nuclides may be either stable or radioactive. If they are stable, their existence must be deduced against a background of stable nuclides, since every known stable nuclide is present on Earth primordially.

==Artificially produced nuclides==
Beyond the naturally occurring nuclides, more than 3000 radionuclides of varying half-lives have been artificially produced and characterized.

The known nuclides are shown in [[Table of nuclides]]. A list of primordial nuclides is given sorted by element, at [[List of elements by stability of isotopes]]. [[List of nuclides]] is sorted by half-life, for the 905 nuclides with half-lives longer than one hour.

==Summary table for numbers of each class of nuclides==
This is a summary table<ref>Table data is derived by counting members of the list; references for the list data itself are given below in the reference section in [[list of nuclides]].</ref> for the 905 nuclides with half-lives longer than one hour, given in [[list of nuclides]]. Note that numbers are not exact, and may change slightly in the future, if some "stable" nuclides are observed to be radioactive with very long half-lives.

{| class="wikitable sortable" width="100%"
! width="300" |Stability class
! Number of nuclides
! [[Running total]]
! Notes on running total
|-
| align="left"| Theoretically stable to all but [[proton decay]]
| align="center"| 90
| align="center"| 90
| Includes first 40 elements. Proton decay yet to be observed.
|-
| Energetically unstable to one or more known decay modes, but no decay yet seen. [[Spontaneous fission]] possible for "stable" nuclides from [[niobium-93]] onward; other mechanisms possible for heavier nuclides. All considered "stable" until decay detected.
| align="center"| 161
| align="center"| 251
| Total of classically [[stable nuclide]]s.
|-
| Radioactive [[primordial nuclide]]s.
| align="center"| 35
| align="center"| 286
| Total primordial elements include [[bismuth]], [[thorium]], and [[uranium]], plus all stable nuclides.
|-
| Radioactive (half-life > 1 hour). Includes most useful [[radioactive tracer]]s.
| align="center"| 619
| align="center"| 905
| [[Carbon-14]] (and other [[cosmogenic nuclide]]s generated by [[cosmic ray]]s); daughters of radioactive primordials, such as [[francium]], etc., and [[nucleogenic]] nuclides from natural nuclear reactions that are other than those from cosmic rays (such as neutron absorption from spontaneous [[nuclear fission]] or [[neutron emission]]). Also many synthetic nuclides.
|-
| Radioactive synthetic (half-life < 1 hour).
| align="center"| >2400
| align="center"| >3300
| Includes all well-characterized synthetic nuclides.
|-
|}

==Nuclear properties and stability ==
[[File:Isotopes and half-life.svg|thumb|right|320px|Stability of nuclides by {{nowrap|(''Z'', ''N'')}}, an example of a [[table of nuclides]]:<br/>
Black – stable (all are primordial)<br/>
Red – primordial radioactive<br/>
Other – radioactive, with decreasing stability from orange to white]]
{{See also|Stable nuclide}}
Atomic nuclei other than hydrogen {{nuclide|H|1}} have protons and neutrons bound together by the [[residual strong force]]. Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their copresence pushes protons slightly apart, reducing the electrostatic repulsion between the protons, and they exert the attractive nuclear force on each other and on protons. For this reason, one or more neutrons are necessary for two or more protons to be bound into a nucleus. As the number of protons increases, so does the ratio of neutrons to protons necessary to ensure a stable nucleus (see graph). For example, although the [[proton–neutron ratio|neutron–proton ratio]] of {{nuclide|He|3|link=yes}} is 1:2, the neutron–proton ratio of {{nuclide|U|238}} is greater than 3:2. A number of lighter elements have stable nuclides with the ratio 1:1 ({{nowrap|1=''Z'' = ''N''}}). The nuclide {{nuclide|Ca|40}} (calcium-40) is observationally the heaviest stable nuclide with the same number of neutrons and protons. All stable nuclides heavier than calcium-40 contain more neutrons than protons.

===Even and odd nucleon numbers===
{{Main|Even and odd atomic nuclei}}
{| class="wikitable" style="float:left; margin-right:1em"
|+'''Even/odd ''Z'', ''N'', and ''A'''''
| style="text-align:right;" | ''A''
! colspan=2 style="text-align:center;" |Even
! colspan=2 style="text-align:center;" |Odd
! rowspan=2 style="text-align:right;" |Total
|-
| style="text-align:right;" | ''Z'',''N''
!EE!!OO
!EO!!OE
|- style="text-align:right;"
! rowspan=2 |Stable
|145||5||53||48
| rowspan=2 |251
|- style="text-align:right;"
| colspan=2 style="text-align:center;" |150
| colspan=2 style="text-align:center;" |101
|- style="text-align:right;"
! rowspan=2 |Long-lived
|22||4||4||5
| rowspan=2 |35
|- style="text-align:right;"
| colspan=2 style="text-align:center;" |26
| colspan=2 style="text-align:center;" |9
|- style="text-align:right;"
! rowspan=2 |All primordial
|167||9||57||53
| rowspan=2 |286
|- style="text-align:right;"
| colspan=2 style="text-align:center;" |176
| colspan=2 style="text-align:center;" |110
|}
The proton–neutron ratio is not the only factor affecting nuclear stability. It depends also on even or odd [[parity (mathematics)|parity]] of its atomic number ''Z'', neutron number ''N'' and, consequently, of their sum, the mass number ''A''. Oddness of both ''Z'' and ''N'' tends to lower the [[nuclear binding energy]], making odd nuclei, generally, less stable. This remarkable difference of nuclear binding energy between neighbouring nuclei, especially of odd-''A'' [[isobar (nuclide)|isobars]], has important consequences: unstable isotopes with a nonoptimal number of neutrons or protons decay by [[beta decay]] (including positron decay), [[electron capture]] or more exotic means, such as [[spontaneous fission]] and [[cluster decay]].

The majority of stable nuclides are even-proton–even-neutron, where all numbers ''Z'', ''N'', and ''A'' are even. The odd-''A'' stable nuclides are divided (roughly evenly) into odd-proton–even-neutron, and even-proton–odd-neutron nuclides. Odd-proton–odd-neutron nuclides (and nuclei) are the least common.

==See also==
*[[Isotope]] (much more information on abundance of stable nuclides)
*[[List of elements by stability of isotopes]]
*[[List of nuclides]] (sorted by half-life)
*[[Table of nuclides]]
*[[Alpha nuclide]]
*[[Monoisotopic element]]
*[[Mononuclidic element]]
*[[Primordial element]]
*[[Radionuclide]]
*[[Hypernucleus]]

==References==
{{Reflist}}

==External links==
*[https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html Livechart - Table of Nuclides] at The International Atomic Energy Agency
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