Editing Isotone

{{Short description|Different nuclides with the same neutron number}}
{{About|a concept in nuclear physics|biochemistry|Isotonicity|the mathematical meaning|monotonic function}}

{{Nuclear physics|cTopic=Nuclides' classification}}

[[File:Isotopes and half-life.svg|thumb|300px|Nuclide half-lives colorcoded]]

Two [[nuclide]]s are '''isotones''' if they have the same [[neutron number]] ''N'', but different [[proton number]] ''Z''. For example, [[Isotopes of boron|boron-12]] and [[carbon-13]] nuclei both contain 7 [[neutron]]s, and so are isotones. Similarly, <sup>36</sup>S, <sup>37</sup>Cl, <sup>38</sup>Ar, <sup>39</sup>K, and <sup>40</sup>Ca nuclei are all isotones of 20 because they all contain 20 neutrons. Despite its similarity to the [[Greek language|Greek]] for "same stretching", the term was formed by the German physicist [[K. Guggenheimer]]<ref>[http://jnm.snmjournals.org/content/19/6/581.full.pdf Nuclear Medicine Begins with a Boa Constrictor], By Marshall Brucer, J Nucl Med 19: 581-598, 1978</ref> by changing the "p" in "[[isotope]]" from "p" for "proton" to "n" for "neutron".<ref>{{cite book |last1=Pauling |first1=Linus |title=General Chemistry |year=1998 |publisher=Dover |isbn=0-486-65622-5 |page=[https://archive.org/details/generalchemistry00paul_0/page/94 94] |url-access=registration |url=https://archive.org/details/generalchemistry00paul_0/page/94 }}</ref>

The largest numbers of [[observationally stable]] nuclides exist for isotones 50 (five: <sup>86</sup>Kr, <sup>88</sup>Sr, <sup>89</sup>Y, <sup>90</sup>Zr, <sup>92</sup>Mo – noting also the [[primordial nuclide|primordial]] [[radionuclide]] <sup>87</sup>Rb) and 82 (six: <sup>138</sup>Ba, <sup>139</sup>La, <sup>140</sup>Ce, <sup>141</sup>Pr, <sup>142</sup>Nd, <sup>144</sup>Sm – noting also the primordial radionuclide <sup>136</sup>Xe). [[Neutron number]]s for which there are no stable isotones are 19, 21, 35, 39, 45, 61, 89, 115, 123, and 127 or more (though 21, 142, 143, 146, and perhaps 150 have primordial radionuclides). In contrast, the [[proton number]]s for which there are no stable isotopes are [[technetium|43]], [[promethium|61]], and [[bismuth|83]] or more (83, [[thorium|90]], [[uranium|92]], and perhaps [[plutonium|94]] have primordial radionuclides).<ref>via [[:File:NuclideMap_stitched.png]]; note also [[Isotopes of bismuth]]</ref> This is related to nuclear [[magic number (physics)|magic numbers]], the number of [[nucleon]]s forming complete [[Nuclear shell model|shells]] within the nucleus, e.g. 2, 8, 20, 28, 50, 82, and 126. No more than one observationally stable nuclide has the same odd neutron number, except for 1 (<sup>2</sup>H and <sup>3</sup>He), 5 (<sup>9</sup>Be and <sup>10</sup>B), 7 (<sup>13</sup>C and <sup>14</sup>N), 55 (<sup>97</sup>Mo and <sup>99</sup>Ru), and 107 (<sup>179</sup>Hf and <sup>180m</sup>Ta). In contrast, all even neutron numbers from 6 to 124, except 84 and 86, have at least two observationally stable nuclides. Neutron numbers for which there is a stable nuclide and a primordial radionuclide are 27 (<sup>50</sup>V), 65 (<sup>113</sup>Cd), 81 (<sup>138</sup>La), 84 (<sup>144</sup>Nd), 85 (<sup>147</sup>Sm), 86 (<sup>148</sup>Sm), 105 (<sup>176</sup>Lu), and 126 (<sup>209</sup>Bi). Neutron numbers for which there are two primordial radionuclides are 88 (<sup>151</sup>Eu and <sup>152</sup>Gd) and 112 (<sup>187</sup>Re and <sup>190</sup>Pt).

The neutron numbers which have only one [[stable nuclide]] (compare: [[monoisotopic element]] for the [[proton number]]s) are: 0, 2, 3, 4, 9, 11, 13, 15, 17, 23, 25, 27, 29, 31, 33, 37, 41, 43, 47, 49, 51, 53, 57, 59, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 84, 85, 86, 87, 91, 93, 95, 97, 99, 101, 103, 105, 109, 111, 113, 117, 119, 121, 125, 126, and the neutron numbers which have only one significant naturally-abundant nuclide (compare: [[mononuclidic element]] for the [[proton number]]s) are: 0, 2, 3, 4, 9, 11, 13, 15, 17, 21, 23, 25, 29, 31, 33, 37, 41, 43, 47, 49, 51, 53, 57, 59, 63, 67, 69, 71, 73, 75, 77, 79, 83, 87, 91, 93, 95, 97, 99, 101, 103, 109, 111, 113, 117, 119, 121, 125, 142, 143, 146.

==See also==
*[[Isotope]]s are nuclides having the same number of [[protons]]: e.g. carbon-12 and carbon-13.
*[[Isobar (nuclide)|Isobar]]s are nuclides having the same [[mass number]] (i.e. sum of protons plus neutrons): e.g. carbon-12 and boron-12.
*[[Nuclear isomer]]s are different excited states of the same type of nucleus. A transition from one isomer to another is accompanied by emission or absorption of a [[gamma ray]], or the process of [[internal conversion]]. (Not to be confused with [[Isomer|chemical isomer]]s.)

==Notes==
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[[Category:Nuclear physics]]