Isotopes of nitrogen

Natural nitrogen (N) consists of two stable isotopes, nitrogen-14, which makes up the vast majority of naturally occurring nitrogen, and nitrogen-15. Fourteen radioactive isotopes (radioisotopes) have also been found so far, with atomic masses ranging from 10 to 25, and one nuclear isomer, ^11mN. All of these radioisotopes are short-lived, with the longest-lived one being nitrogen-13 with a half-life of 9.965 minutes. All of the others have half-lives below 7.15 seconds, with most of these being below five-eighths of a second. Most of the isotopes with atomic mass numbers below 14 decay to isotopes of carbon, while most of the isotopes with masses above 15 decay to isotopes of oxygen. The shortest-lived known isotope is nitrogen-10, with a half-life of about 2.3 microseconds.

The relative atomic mass of nitrogen is 14.0067.

Natural isotopes

Nitrogen-14

Nitrogen-14 is one of two stable (non-radioactive) isotopes of the chemical element nitrogen, which makes about 99.636% of natural nitrogen.

Nitrogen-14 is one of the very few stable nuclides with both an odd number of protons and of neutrons (seven each). Each of these contributes a nuclear spin of plus or minus spin 1/2, giving the nucleus a total magnetic spin of one.

Like all elements heavier than lithium, the original source of nitrogen-14 and nitrogen-15 in the Universe is believed to be stellar nucleosynthesis, where they are produced as part of the carbon-nitrogen-oxygen cycle.

Nitrogen-14 is the source of naturally-occurring carbon-14. Some kinds of cosmic radiation cause a nuclear reaction with nitrogen-14 in the upper atmosphere of the Earth, creating carbon-14, which decays back to nitrogen-14 with a half-life of 5,730±40 years.

Nitrogen-15

Nitrogen-15 is a rare stable isotope of nitrogen. This isotope is often used in agricultural and medical research, for example in the Meselson–Stahl experiment to establish the nature of DNA replication. An extension of this research resulted in development of DNA-based stable-isotope probing, which allows examination of links between metabolic function and taxonomic identity of microorganisms in the environment, without the need for culture isolation. Nitrogen-15 is extensively used to trace mineral nitrogen compounds (particularly fertilizers) in the environment and when combined with the use of other isotopic labels, is also a very important tracer for describing the fate of nitrogenous organic pollutants.

Nitrogen-15 is frequently used in NMR (Nitrogen-15 NMR spectroscopy), because unlike the more abundant nitrogen-14, that has an integer nuclear spin and thus a quadrupole moment, N-15 has a fractional nuclear spin of one-half, which offers advantages for NMR like narrower line width. Proteins can be isotopically labelled by cultivating them in a medium containing nitrogen-15 as the only source of nitrogen. In addition, nitrogen-15 is used to label proteins in quantitative proteomics (e.g. SILAC).

Also, the ratio of ¹⁵N/¹⁴N in an organism can give clues about its diet, as movement up the food chain tends to concentrate the ¹⁵N isotope, by 3–4‰ with each step of the food chain (see Isotopic signatures – Nitrogen Isotopes).

Nitrogen-15 presents one of the lowest thermal neutron capture cross sections of all isotopes.

Two sources of nitrogen-15 are the positron emission of oxygen-15 and the beta decay of carbon-15.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
10N	7	3	10.04165(43)	200(140)×10−24 s [2.3(16) MeV]	p	9C	(2−)
11N	7	4	11.02609(5)	590(210)×10−24 s [1.58(+75−52) MeV]	p	10C	1/2+
11mN	740(60) keV			6.90(80)×10−22 s			1/2−
12N	7	5	12.0186132(11)	11.000(16) ms	β+ (96.5%)	12C	1+
					β+, α (3.5%)	8Be
13N	7	6	13.00573861(29)	9.965(4) min	β+	13C	1/2−
14N	7	7	14.0030740048(6)	Stable			1+	0.99636(20)	0.99579–0.99654
15N	7	8	15.0001088982(7)	Stable			1/2−	0.00364(20)	0.00346–0.00421
16N	7	9	16.0061017(28)	7.13(2) s	β− (99.99%)	16O	2−
					β−, α (.001%)	12C
17N	7	10	17.008450(16)	4.173(4) s	β−, n (95.0%)	16O	1/2−
					β− (4.99%)	17O
					β−, α (.0025%)	13C
18N	7	11	18.014079(20)	622(9) ms	β− (76.9%)	18O	1−
					β−, α (12.2%)	14C
					β−, n (10.9%)	17O
19N	7	12	19.017029(18)	271(8) ms	β−, n (54.6%)	18O	(1/2−)
					β− (45.4%)	19O
20N	7	13	20.02337(6)	130(7) ms	β−, n (56.99%)	19O
					β− (43.00%)	20O
21N	7	14	21.02711(10)	87(6) ms	β−, n (80.0%)	20O	1/2−#
					β− (20.0%)	21O
22N	7	15	22.03439(21)	13.9(14) ms	β− (65.0%)	22O
					β−, n (35.0%)	21O
23N	7	16	23.04122(32)#	14.5(24) ms [14.1(+12−15) ms]	β−	23O	1/2−#
24N	7	17	24.05104(43)#	<52 ns	n	23N
25N	7	18	25.06066(54)#	<260 ns			1/2−#

Notes

• The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.
• Nuclide masses are given by IUPAP Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO).
• Isotope abundances are given by IUPAC Commission on Isotopic Abundances and Atomic Weights.

References

• Isotope masses from:
• Isotopic compositions and standard atomic masses from:
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Isotopes of carbon	Isotopes of nitrogen	Isotopes of oxygen
Table of nuclides