Editing Nitrogen (section)

===Isotopes===
{{main|Isotopes of nitrogen}}
[[File:NuclideMap C-F.png|thumb|right|upright=2.3|Table of nuclides (Segrè chart) from carbon to fluorine (including nitrogen). Orange indicates [[proton emission]] (nuclides outside the proton drip line); pink for [[positron emission]] (inverse beta decay); black for [[stable nuclide|stable]] nuclides; blue for [[electron emission]] (beta decay); and violet for [[neutron emission]] (nuclides outside the neutron drip line). Proton number increases going up the vertical axis and neutron number going to the right on the horizontal axis.]]
Nitrogen has two stable [[isotope]]s: <sup>14</sup>N and <sup>15</sup>N. The first is much more common, making up 99.634% of natural nitrogen, and the second (which is slightly heavier) makes up the remaining 0.366%. This leads to an atomic weight of around 14.007&nbsp;u.<ref name="Greenwood411">Greenwood and Earnshaw, pp. 411–12</ref> Both of these stable isotopes are produced in the [[CNO cycle]] in [[star]]s, but <sup>14</sup>N is more common as its proton capture is the rate-limiting step. <sup>14</sup>N is one of the five stable [[even and odd atomic nuclei|odd–odd nuclides]] (a nuclide having an odd number of protons and neutrons); the other four are [[deuterium|<sup>2</sup>H]], <sup>6</sup>Li, <sup>10</sup>B, and <sup>180m</sup>Ta.<ref name="BetheBible">{{cite journal|last=Bethe |first=H. A.|date=1939|title=Energy Production in Stars|journal=[[Physical Review]]|volume=55 |issue=5 |pages=434–56|bibcode=1939PhRv...55..434B|doi= 10.1103/PhysRev.55.434|pmid=17835673|doi-access=free}}</ref>

The relative abundance of <sup>14</sup>N and <sup>15</sup>N is practically constant in the atmosphere but can vary elsewhere, due to natural isotopic fractionation from biological [[redox]] reactions and the evaporation of natural [[ammonia]] or [[nitric acid]].<ref name=CIAAWnitrogen/> Biologically mediated reactions (e.g., [[Assimilation (biology)|assimilation]], [[nitrification]], and [[denitrification]]) strongly control nitrogen dynamics in the soil. These reactions typically result in <sup>15</sup>N enrichment of the [[Substrate (chemistry)|substrate]] and depletion of the [[Product (chemistry)|product]].<ref name="enrich">{{cite book | url = https://books.google.com/books?id=U9y3whFC2DIC&pg=PA74 | pages = 74–75 | title = Stable Isotopes and Biosphere – Atmosphere Interactions: Processes and Biological Controls | isbn = 978-0-08-052528-0 | last1 = Flanagan | first1 = Lawrence B. | last2 = Ehleringer | first2 = James R. | last3 = Pataki | first3 = Diane E. | date = 15 December 2004 | publisher = Elsevier | access-date = 20 December 2015 | archive-date = 5 February 2016 | archive-url = https://web.archive.org/web/20160205191759/https://books.google.com/books?id=U9y3whFC2DIC&pg=PA74 | url-status = live }}</ref>

The heavy isotope <sup>15</sup>N was first discovered by S. M. Naudé in 1929, and soon after heavy isotopes of the neighbouring elements [[oxygen]] and [[carbon]] were discovered.<ref name="Greenwood408">Greenwood and Earnshaw, p. 408</ref> It presents one of the lowest thermal neutron capture cross-sections of all isotopes.<ref>{{cite web |url=http://www.nndc.bnl.gov/sigma/index.jsp?as=15&lib=endfb7.1&nsub=10 |title=Evaluated Nuclear Data File (ENDF) Retrieval & Plotting |publisher=National Nuclear Data Center |access-date=2016-11-23 |archive-date=2020-08-09 |archive-url=https://web.archive.org/web/20200809124433/https://www.nndc.bnl.gov/sigma/index.jsp?as=15&lib=endfb7.1&nsub=10 |url-status=live }}</ref> It is frequently used in [[nuclear magnetic resonance]] (NMR) spectroscopy to determine the structures of nitrogen-containing molecules, due to its fractional [[nuclear spin]] of one-half, which offers advantages for NMR such as narrower line width. <sup>14</sup>N, though also theoretically usable, has an integer nuclear spin of one and thus has a [[quadrupole moment]] that leads to wider and less useful spectra.<ref name="Greenwood411" /> <sup>15</sup>N NMR nevertheless has complications not encountered in the more common <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy. The low natural abundance of <sup>15</sup>N (0.36%) significantly reduces sensitivity, a problem which is only exacerbated by its low [[gyromagnetic ratio]], (only 10.14% that of <sup>1</sup>H). As a result, the signal-to-noise ratio for <sup>1</sup>H is about 300 times as much as that for <sup>15</sup>N at the same magnetic field strength.<ref name="autogenerated2007">{{cite book| author=Arthur G Palmer| title=Protein NMR Spectroscopy| publisher=Elsevier Academic Press| date=2007 | isbn = 978-0-12-164491-8}}</ref> This may be somewhat alleviated by isotopic enrichment of <sup>15</sup>N by chemical exchange or fractional distillation. <sup>15</sup>N-enriched compounds have the advantage that under standard conditions, they do not undergo chemical exchange of their nitrogen atoms with atmospheric nitrogen, unlike compounds with labelled [[hydrogen]], carbon, and oxygen isotopes that must be kept away from the atmosphere.<ref name="Greenwood411" /> The <sup>15</sup>N:<sup>14</sup>N ratio is commonly used in stable isotope analysis in the fields of [[geochemistry]], [[hydrology]], [[paleoclimatology]] and [[paleoceanography]], where it is called [[δ15N|''δ''<sup>15</sup>N]].<ref>{{cite book | last=Katzenberg | first=M. A. | title=Biological Anthropology of the Human Skeleton | chapter=Chapter 13: Stable Isotope Analysis: A Tool for Studying Past Diet, Demography, and Life History | year=2008 | publisher=Wiley | edition=2nd | isbn=978-0-471-79372-4 }}</ref>

Of the thirteen other isotopes produced synthetically, ranging from <sup>9</sup>N to <sup>23</sup>N, [[nitrogen-13|<sup>13</sup>N]] has a [[half-life]] of ten minutes and the remaining isotopes have half-lives less than eight seconds.<ref name=N9sci>{{cite news |url=https://www.science.org/content/article/fleeting-form-nitrogen-stretches-nuclear-theory-its-limits |title=Fleeting form of nitrogen stretches nuclear theory to its limits |last=Cho |first=Adrian |website=[[science.org]] |date=25 September 2023 |access-date=27 September 2023}}</ref><ref name="NUBASE">{{NUBASE 2003}}</ref> Given the half-life difference, <sup>13</sup>N is the most important nitrogen radioisotope, being relatively long-lived enough to use in [[positron emission tomography]] (PET), although its half-life is still short and thus it must be produced at the venue of the PET, for example in a [[cyclotron]] via proton bombardment of <sup>16</sup>O producing <sup>13</sup>N and an [[alpha particle]].<ref name="Carlson 151">{{cite book | last = Carlson | first = Neil | title = Physiology of Behavior | publisher = Pearson | series = Methods and Strategies of Research | volume = 11th edition | date = January 22, 2012 | page = 151 | isbn = 978-0-205-23939-9}}</ref>

The [[radioisotope]] <sup>16</sup>N is the dominant [[radionuclide]] in the coolant of [[pressurised water reactor]]s or [[boiling water reactor]]s during normal operation. It is produced from <sup>16</sup>O (in water) via an [[Np reaction|(n,p) reaction]], in which the <sup>16</sup>O atom captures a neutron and expels a proton. It has a short half-life of about 7.1&nbsp;s,<ref name="NUBASE" /> but its decay back to <sup>16</sup>O produces high-energy [[gamma radiation]] (5 to 7&nbsp;MeV).<ref name="NUBASE" /><ref name="Neeb">{{Cite book|last=Neeb|first=Karl Heinz|title=The Radiochemistry of Nuclear Power Plants with Light Water Reactors|publisher=Walter de Gruyter|location=Berlin-New York|date=1997|isbn=978-3-11-013242-7|url=https://books.google.com/books?id=SJOE00whg44C&pg=PA227|page=227|access-date=2015-12-20|archive-date=2016-02-05|archive-url=https://web.archive.org/web/20160205191759/https://books.google.com/books?id=SJOE00whg44C&pg=PA227|url-status=live}}</ref> Because of this, access to the primary coolant piping in a pressurised water reactor must be restricted during [[Nuclear reactor|reactor]] power operation.<ref name="Neeb" /> It is a sensitive and immediate indicator of leaks from the primary coolant system to the secondary steam cycle and is the primary means of detection for such leaks.<ref name="Neeb"/>