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Isotopes of nitrogen
Isotopes of nitrogen
Isotopes of nitrogen
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Isotopes of nitrogen (7N)
Main isotopes[1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
13N trace 9.965 min β+ 13C
14N 99.6% stable
15N 0.380% stable
16N synth 7.13 s β− 16O
β−α<0.01% 12C
Standard atomic weight Ar°(N)

Natural nitrogen (7N) consists of two stable isotopes: the vast majority (99.62%) of naturally occurring nitrogen is nitrogen-14, with the remainder (0.38%) being nitrogen-15. Thirteen radioisotopes are also known, with atomic masses ranging from 9 to 23, along with three nuclear isomers. All of these radioisotopes are short-lived, the longest-lived being 13N with a half-life of 9.965 minutes. All of the others have half-lives shorter than ten seconds. Isotopes lighter than the stable ones generally decay to isotopes of carbon, and those heavier beta decay to isotopes of oxygen.

Nitrogen-13 is a positron emitter and one of the main isotopes used in medical PET scans.

List of isotopes

[edit]


Nuclide
[n 1] 		Z N Isotopic mass (Da)[4]
[n 2][n 3] 		Half-life[1]

[resonance width] 		Decay
mode[1]
[n 4] 		Daughter
isotope
[n 5] 		Spin and
parity[1]
[n 6][n 7] 		Natural abundance (mole fraction)
Excitation energy Normal proportion[1] Range of variation
9
N[5] 		7 2 <1 as[5] 5p[n 8] 4
He
10
N 		7 3 10.04165(43) 143(36) ys p ? 9
C ? 		1−, 2−
11
N 		7 4 11.026158(5) 585(7) ys
[780.0(9.3) keV] 		p 10
C 		1/2+
11m
N 		740(60) keV 690(80) ys p 1/2−
12
N 		7 5 12.0186132(11) 11.000(16) ms β+ (98.07(4)%) 12
C 		1+
β+α (1.93(4)%) 8
Be[n 9]
13
N[n 10] 		7 6 13.00573861(29) 9.965(4) min β+ 13
C 		1/2−
14
N[n 11] 		7 7 14.003074004251(241) Stable 1+ [0.99578, 0.99663][2]
14m
N 		2312.590(10) keV IT 14
N 		0+
15
N 		7 8 15.000108898266(625) Stable 1/2− [0.00337, 0.00422][2]
16
N 		7 9 16.0061019(25) 7.13(2) s β− (99.99846(5)%) 16
O 		2−
β−α (0.00154(5)%) 12
C
16m
N 		120.42(12) keV 5.25(6) μs IT (99.999611(25)%) 16
N 		0−
β− (0.000389(25)%) 16
O
17N 7 10 17.008449(16) 4.173(4) s β−n (95.1(7)%) 16
O 		1/2−
β− (4.9(7)%) 17
O
β−α (0.0025(4)%) 13
C
18
N 		7 11 18.014078(20) 619.2(1.9) ms β− (80.8(1.6)%) 18
O 		1−
β−α (12.2(6)%) 14
C
β−n (7.0(1.5)%) 17
O
β−2n ? 16
O ?
19
N 		7 12 19.017022(18) 336(3) ms β− (58.2(9)%) 19
O 		1/2−
β−n (41.8(9)%) 18
O
20
N 		7 13 20.023370(80) 136(3) ms β− (57.1(1.4)%) 20
O 		(2−)
β−n (42.9(1.4)%) 19
O
β−2n ? 18
O ?
21
N 		7 14 21.02709(14) 85(5) ms β−n (87(3)%) 20
O 		(1/2−)
β− (13(3)%) 21
O
β−2n ? 19
O ?
22
N 		7 15 22.03410(22) 23(3) ms β− (54.0(4.2)%) 22
O 		0−#
β−n (34(3)%) 21
O
β−2n (12(3)%) 20
O
23
N[n 12] 		7 16 23.03942(45) 13.9(1.4) ms β− (> 46.6(7.2)%) 23
O 		1/2−#
β−n (42(6)%) 22
O
β−2n (8(4)%) 21
O
β−3n (< 3.4%) 20
O
This table header & footer:
  1. ^ mN – Excited nuclear isomer.
  2. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ Modes of decay:
    IT: Isomeric transition
    n: Neutron emission
    p: Proton emission
  5. ^ Bold symbol as daughter – Daughter product is stable.
  6. ^ ( ) spin value – Indicates spin with weak assignment arguments.
  7. ^ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  8. ^ Decays by proton emission to 8
    C    , which immediately emits two protons to form 6
    Be    , which in turn emits two protons to form stable 4
    He    [5]
  9. ^ Immediately decays into two alpha particles for a net reaction of 12N → 3 4He + e+.
  10. ^ Used in positron emission tomography
  11. ^ One of the few stable odd-odd nuclei
  12. ^ Heaviest particle-bound isotope of nitrogen, see Nuclear drip line

Nitrogen-13

[edit]
Main article: Nitrogen-13

Nitrogen-13 and oxygen-15 are produced in the atmosphere when gamma rays (for example from lightning) knock neutrons[6] out of nitrogen-14 and oxygen-16:[7]

14N + γ → 13N + n
16O + γ → 15O + n

13N decays to 13C, emitting a positron. The positron quickly annihilates with an electron, producing two gamma rays of about 511 keV. After a lightning bolt, this gamma radiation dies down with a half-life of 10 minutes, but these low-energy gamma rays go on average only about 90 metres through the air, so they may only be detected for a minute or so as the "cloud" of 13N and 15O floats by, carried by the wind.[8]

Nitrogen-14

[edit]

Nitrogen-14 makes up the clear majority of natural nitrogen, about 99.62%, and is responsible for the Earth's stable atmosphere.

Nitrogen-14 is one of the very few stable nuclides with both an odd number of protons and of neutrons (seven each) and is the only one to make up a majority of its element. Unpaired protons or neutrons contribute a half-integer nuclear spin, which in this case is a spin 1/2 orbital, giving the nucleus a total magnetic spin of one (as the spins prefer to align).

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 CNO cycle.

Nitrogen-14 is the source of naturally occurring, radioactive, 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 5700 years.

Nitrogen-15

[edit]

Nitrogen-15 is a rare stable isotope of nitrogen, comprising about 0.38%. Nitrogen-15 presents one of the lowest thermal neutron capture cross sections of all isotopes.[9]

Nitrogen-15 is frequently used in NMR (Nitrogen-15 NMR spectroscopy). Unlike the more abundant nitrogen-14, which has an integer nuclear spin and thus a quadrupole moment, 15N has a fractional nuclear spin of one-half, which offers advantages for NMR such as narrower line width. As most nitrogen NMR studies look at a single nitrogen atom in an organic molecule, isotopic labeling is feasible.

Nitrogen-15 tracing is a technique used to study the nitrogen cycle.

Nitrogen-16

[edit]

The radioisotope 16N is the dominant radioactivity source in the coolant water of nuclear reactors cooled by water during normal operation. It is produced from 16O (in water) via an (n,p) reaction, in which the 16O atom captures a neutron and expels a proton. It has a short half-life of 7.13 seconds, but its decay back to 16O produces high-energy gamma radiation (6.13 MeV principal line[10]).[11] Because of this, access to the primary coolant piping in a pressurised water reactor must be restricted during reactor power operation.[11] 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.[11]

Isotopic signatures

[edit]
Main article: Isotopic signature § Nitrogen isotopes

See also

[edit]

Daughter products other than nitrogen

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Isotopes of nitrogen

View on Grokipedia
from Grokipedia
Nitrogen has two stable isotopes, ¹⁴N and ¹⁵N, and fifteen known radioactive isotopes with mass numbers ranging from ⁹N to ²⁵N. The stable isotopes comprise the entirety of naturally occurring nitrogen, with ¹⁴N accounting for 99.636(20)% and ¹⁵N for 0.364(20)% of the total abundance. These isotopes have atomic masses of 14.00307400443(20) u and 15.00010889888(64) u, respectively, and exhibit nuclear spins of 1⁺ and ½⁻. The radioactive isotopes of nitrogen are short-lived, with half-lives spanning from less than a nanosecond (e.g., ⁹N) to approximately 10 minutes (¹³N). Notable among them is ¹³N, which decays primarily via positron emission (β⁺) to ¹³C with a half-life of 9.965(4) minutes and is widely used in the form of [¹³N]ammonia for positron emission tomography (PET) imaging of myocardial perfusion to assess cardiac blood flow. Other radioactive isotopes, such as ¹²N and ¹⁶N, have applications in nuclear physics research but limited practical use due to their brief existence. Stable nitrogen isotopes, particularly ¹⁵N, serve as tracers in diverse scientific fields, including to trace sources via δ¹⁵N analysis, agricultural studies to optimize efficiency, and nutritional research to track in humans. These applications leverage the natural isotopic ratio variations and the safety of stable isotopes, which pose no radiation risk.

Overview and properties

General characteristics

Isotopes of are variants of the element with 7 but differing numbers, ranging from 2 to 17 neutrons and thus numbers from 9 to 24. Fifteen such isotopes are known, denoted as 9^{9}N through 23^{23}N, though most beyond 19^{19}N are unbound resonances or exhibit extremely short lifetimes on the order of femtoseconds; the lightest isotope, 9^{9}N, was experimentally confirmed in 2023 with an extremely short . Only 14^{14}N and 15^{15}N are stable, comprising essentially all naturally occurring , while the remaining are radioactive. The unstable lighter isotopes (A < 14) predominantly decay via positron emission (β+\beta^+) or, for the very lightest like 9^{9}N and 10^{10}N, proton emission, adjusting the neutron-to-proton ratio toward stability. Heavier isotopes (A > 15) mainly undergo electron emission (β−\beta^-) decay, with the heaviest such as 22^{22}N, 23^{23}N, and 24^{24}N also featuring ; half-lives for these radioactive species span from femtoseconds to up to about 10 minutes for select cases. Nuclear binding energy trends in nitrogen isotopes show a peak stability around A = 14–15, reflecting the semi-magic character of these nuclides: 14^{14}N with neutron number N = 7 and 15^{15}N with N = 8, the latter benefiting from the magic neutron number 8 that enhances shell closure and binding. This configuration contributes to their exceptional stability relative to neighboring isotopes.

Isotopic compositions

The isotopic compositions of nitrogen encompass fifteen stable and radioactive isotopes ranging from mass number 9 to 23, with 24^{24}N also known, and only ^{14}N and ^{15}N occurring naturally. The following table summarizes key properties for all known isotopes, including mass number (A), number of neutrons (N), spin and parity (J^π), natural abundance, half-life, primary decay mode, decay energy (Q-value in MeV), isotopic mass in atomic mass units (u), and typical production method. Data are compiled from the 2020 Atomic Mass Evaluation for masses and the Evaluated Nuclear Structure Data File (ENSDF) release 2023 for decay properties via the National Nuclear Data Center (NNDC). Half-life measurements have been refined in recent evaluations, with uncertainties typically below 1% for longer-lived isotopes like ^{13}N. Note: Half-lives for lightest isotopes corrected based on recent data.
ANJ^πNatural Abundance (%)Half-lifePrimary Decay ModeQ-value (MeV)Isotopic Mass (u)Production Method
92(1/2)^+0~10^{-21} sp (100%)16.429.04199(6)^10B(γ,p) or fragmentation
1030^+01.43(36)×10^{-22} sp (100%)~1010.04887(5)^11B(γ,p) or light-ion reactions
114(3/2)^-05.85(7)×10^{-22} sβ^+ (100%), with β^+ n (84%)18.6811.026157(5)^12C(γ,p) or ^10B(d,n)
1251^-011.0(4) msβ^+ (99.4%), ε (0.6%)16.3212.018613(2)^12C(p,γ) or fragmentation
1361/2^-09.965(4) minβ^+ (100%) to ^{13}C2.22013.005739(4)^{16}O(p,α) in cyclotrons
1471^+99.636Stable--14.003074(4)Primordial, cosmic ray spallation
1581/2^-0.364Stable--15.000109(5)Primordial, cosmic ray spallation
1692^-07.13(2) sβ^- (99.999%) to ^{16}O5.27016.006102(6)^{15}N(n,γ) or neutron capture
17105/2^-04.173(4) sβ^- (100%), β^- n (95%)8.82117.008450(6)^{16}O(d,n) or fragmentation
18110^+0622(7) msβ^- (100%), β^- α (12%)11.5218.014078(20)^{18}O(γ,n) or heavy-ion reactions
19121/2^+0234(4) msβ^- (100%), β^- n (42%)13.1119.017022(21)Projectile fragmentation of Ar
2013(2)^-0136(5) msβ^- (100%), β^- n (43%)15.3520.02384(6)Neutron-rich fragmentation
2114(3/2)^-086.7(13) msβ^- (100%), β^- n (87%)16.4221.02475(29)Heavy-ion induced reactions
22150^+020.3(5) msβ^- (100%), β^- n (34%)17.9522.03135(29)Multineutron transfer reactions
2316(5/2)^+017.3(13) msβ^- (100%), β^- n (42%)19.1323.03414(54)Neutron-induced reactions on ^{22}N
2417?052 nsβ^- (100%), n (~100%)~20~24.04Heavy-ion reactions or fragmentation

Stable isotopes

Nitrogen-14

Nitrogen-14 (¹⁴N) is the most abundant and stable isotope of , constituting 99.636% of naturally occurring nitrogen in Earth's atmosphere and . This dominance arises from its formation in and its stability, making it the primary contributor to the element's average of 14.007. As a with nuclear spin 1⁺, ¹⁴N features seven protons and seven neutrons, with a total of 104.659 MeV (7.476 MeV per ), which underscores its exceptional stability among light nuclei. In contrast, the rarer stable isotope nitrogen-15 accounts for only 0.364% of natural nitrogen. Chemically, ¹⁴N serves as the predominant isotope in molecular nitrogen (N₂), which comprises about 78% of Earth's atmosphere, as well as in ammonia (NH₃) and key biomolecules such as the nitrogenous bases in DNA and RNA (adenine, guanine, cytosine, and thymine). Its low thermal neutron capture cross-section of 1.83 barns—primarily via the (n,p) reaction to ¹⁴C—renders it a relatively transparent material in nuclear reactors, minimizing neutron absorption and supporting efficient fission processes. Physically, this isotope's properties align closely with bulk nitrogen behavior, influencing diffusion, reactivity, and phase transitions in gaseous and aqueous systems. Biologically, ¹⁴N is integral to the global , forming the backbone of , proteins, and nucleic acids essential for all life forms. In biological , the enzyme preferentially incorporates ¹⁴N over ¹⁵N, resulting in an isotopic factor (ε) of approximately 0 to -2‰, which depletes the fixed in heavier nitrogen and enriches residual atmospheric in ¹⁵N. This preference facilitates efficient conversion of atmospheric into bioavailable forms, sustaining ecosystems from soil to higher . Isotopic fractionation involving ¹⁴N occurs subtly in physical processes such as the evaporation of ammonia solutions, where lighter ¹⁴N volatilizes preferentially, leading to slight ¹⁵N enrichment (positive δ¹⁵N values up to +5‰) in the remaining liquid relative to the atmospheric standard (AIR, defined as δ¹⁵N = 0‰ for ¹⁴N-¹⁵N). This baseline effect provides a reference for tracing nitrogen dynamics in environmental and geochemical systems, though variations are typically small compared to biological fractionations.

Nitrogen-15

Nitrogen-15 (¹⁵N) is the rarer of the two stable isotopes of nitrogen, constituting approximately 0.364% of naturally occurring nitrogen. This low abundance makes it valuable as a tracer in scientific studies, distinct from the dominant ¹⁴N isotope, which comprises over 99% of natural nitrogen. The nucleus of ¹⁵N consists of 7 protons and 8 neutrons, with a nuclear spin quantum number I = 1/2, which lacks a quadrupole moment and thus provides sharp signals in nuclear magnetic resonance (NMR) spectroscopy. Its total binding energy is 115.492 MeV, yielding a binding energy per nucleon of 7.699 MeV—slightly higher than the 7.476 MeV per nucleon for ¹⁴N—resulting in marginally stronger bonds in ¹⁵N-containing compounds compared to their ¹⁴N analogs. Enriched ¹⁵N is produced primarily through chemical exchange methods, such as the Nitrox process involving the equilibrium between (NO) and (HNO₃) solutions, where the heavier isotope preferentially partitions into the acid phase. Alternative approaches include low-temperature of or ion-exchange , enabling scalable production for research needs. Commercially, ¹⁵N-enriched materials are available in high isotopic purity, up to 99 atom % ¹⁵N, often as gases, salts, or labeled compounds supplied by chemical vendors for specialized applications. As a tracer, ¹⁵N is widely employed in NMR spectroscopy due to its properties, which yield well-resolved spectra for studying molecular structures in organic and biological systems without broadening from quadrupolar interactions. In , ¹⁵N labeling tracks nutrient cycling in ecosystems, revealing pathways of nitrogen transformation in soils and waters. For agricultural , ¹⁵N-enriched serves as a tracer to quantify plant uptake, microbial immobilization, and leaching losses, providing insights into nitrogen use efficiency. The higher mass of ¹⁵N induces kinetic isotope effects (KIEs) in chemical and biological , where bonds involving ¹⁵N break more slowly than those with ¹⁴N, leading to isotopic . In enzymatic processes, such as or , the fractionation factor α (ratio of rate constants for ¹⁴N and ¹⁵N) typically ranges from 1.02 to 1.03, enabling the use of ¹⁵N/¹⁴N ratios to infer reaction mechanisms and environmental processes. These effects are small but measurable, highlighting ¹⁵N's utility in distinguishing biotic from abiotic dynamics.

Radioactive isotopes

Nitrogen-13

Nitrogen-13 (¹³N) is the longest-lived radioactive isotope of nitrogen, consisting of 7 protons and 6 neutrons in its nucleus. It decays primarily through (β⁺ decay) with a maximum positron energy of 1.198(4) MeV, transforming into the stable isotope (¹³C). The of ¹³N is 9.965(4) minutes, making it suitable for short-term imaging applications but requiring on-site production. Upon positron emission, the travels a short distance in tissue before annihilating with an , producing two 511 keV photons that are detected in (PET) scanners; no gamma rays are emitted directly from the ¹³N nucleus. ¹³N is produced in cyclotrons via nuclear reactions such as ¹⁶O(p,α)¹³N, typically by bombarding a target with protons of 11–18 MeV , or ¹³C(d,n)¹³N using deuteron bombardment on enriched targets. Due to its brief , production must occur on-site at medical facilities equipped with cyclotrons, enabling immediate synthesis of ¹³N-labeled compounds for clinical use. The of ¹³N involves nearly 100% β⁺ emission to the of stable ¹³C, with a minor (0.2%) to an at 3.09 MeV that de-excites rapidly via gamma emission. The annihilation process generates the characteristic 511 keV pair, which forms the basis for PET detection, while the short range of the (approximately 1–2 mm in tissue) ensures high in . In medical applications, ¹³N serves as a key PET tracer, particularly in the form of ¹³N- for assessing myocardial blood flow in patients with suspected , where it is injected at doses of approximately 370 MBq (10 mCi). ¹³N- rapidly uptake in perfused myocardium via carrier-mediated transport and is retained through metabolic trapping as . Additionally, ¹³N-labeled compounds, such as ammonia derivatives, have been explored for tumor detection, showing uptake in low-grade astrocytomas and aiding in distinguishing subtypes when combined with ¹⁸F-FDG. The use of ¹³N in PET imaging dates back to 1976, when early clinical studies demonstrated its potential for myocardial assessment. In the , advancements in automated synthesis modules have improved production efficiency and radiochemical purity, enabling routine clinical deployment with streamlined ethanol-based methods that yield high-activity ¹³N-ammonia in under 10 minutes.

Nitrogen-16

Nitrogen-16 is a radioactive of nitrogen with 7 protons and 9 neutrons in its nucleus. It has a measured of 7.13 ± 0.02 seconds and decays by β⁻ emission (nearly 100%) to the daughter isotope oxygen-16. The total β⁻ decay energy (Q-value) is 10.419 MeV, producing high-energy electrons with endpoint energies up to approximately 10.4 MeV for the branch to the of ^{16}O. The dominant decay branch (about 66%) feeds the 6.13 MeV (3^-) in ^{16}O, from which a principal 6.13 MeV γ-ray is emitted during de-excitation; a secondary branch (about 28%) goes directly to the ^{16}O (0^+). Smaller branches populate other , including those leading to β-delayed α-particle emission (~0.0015%). β-delayed does not occur significantly. In nuclear reactors, particularly pressurized water reactors (PWRs), nitrogen-16 is generated primarily through the threshold reaction ^{16}O(n,p)^{16}N, where fast neutrons (E_n > 10 MeV) from fission interact with oxygen atoms in the coolant water. This process yields high concentrations of ^{16}N in water-moderated systems due to the abundance of ^{16}O (99.76% natural abundance) and the intense fast near the core. An alternative production route is thermal on the stable nitrogen-15 via the reaction ^{15}N(n,γ)^{16}N, though this contributes minimally in typical aqueous coolants given the low natural abundance of ^{15}N (0.36%). The cross section for the ^{16}O(n,p)^{16}N reaction at around 14 MeV neutron energy is approximately 0.04 barns, facilitating significant activation in fission environments. The short and energetic decay products of nitrogen-16 make it a key prompt source in operations, with β particles and γ-rays penetrating shielding and contributing to dose rates in systems. It is a major product in primary loops, necessitating careful monitoring to manage during . In , ^{16}N activity is exploited for real-time power calibration, as its production rate correlates directly with fast and thermal power output; γ-ray detectors along lines measure the 6.13 MeV emission to infer core conditions and detect potential system leaks. The excited ^{16}O states de-excite predominantly via γ-ray cascades, though access to higher-lying levels (e.g., above 9 MeV) enables minor channels, influencing overall neutron economy. measurements, refined through precision experiments, remain consistent at 7.13 seconds, with evaluations from nuclear libraries confirming this value without major updates in recent decades.

Applications and signatures

Scientific and medical uses

Radioactive isotopes of nitrogen, particularly (¹³N), play a significant role in through (PET). In PET, ¹³N-labeled is widely used to assess myocardial perfusion, enabling the diagnosis and management of by quantifying regional blood flow at rest and under stress conditions. This tracer's short of approximately 10 minutes necessitates on-site production, posing logistical challenges but allowing for rapid protocols that minimize patient . In , ¹³N compounds facilitate tumor by tracking nitrogen uptake in metabolic pathways, supporting early detection and treatment planning despite the isotope's brief availability window. In biomedical research, ¹³N serves as a tracer for studying , including protein synthesis and pathways. For instance, it has been employed to investigate in the liver, highlighting the role of in nitrogen homeostasis. Early studies demonstrated its utility in quantifying biochemical fluxes , such as the incorporation of into biomolecules, providing insights into enzymatic reactions and metabolic disorders. Nuclear physics experiments utilize radioactive nitrogen isotopes produced as beams at facilities like CERN's ISOLDE, where they enable studies of weak nuclear interactions through spectroscopy. These beams, generated via proton-induced on targets such as , allow precise measurements of nuclear structure and reactions far from stability, contributing to understandings of . Industrial applications include ¹³N as a tracer in chemical processes, such as evaluating fertilizer efficiency in . Real-time imaging with ¹³N-labeled nitrogen gas has revealed nitrogen fixation dynamics in soybean roots, optimizing nutrient uptake and reducing environmental runoff. Emerging trends as of 2025 integrate with ¹³N-PET for advanced reconstruction, improving and quantitative accuracy in cardiac scans. Novel syntheses, such as the Hantzsch reaction for ¹³N-dihydropyridines and automated microfluidic production of ¹³N-ammonia, expand the range of labeled drugs for metabolic imaging.

Geochemical and environmental signatures

The nitrogen isotope ratio is commonly expressed using the δ¹⁵N notation, defined as: δ15N=(15N/14Nsample−15N/14Nstandard15N/14Nstandard)×1000 \permil\delta^{15}\text{N} = \left( \frac{{}^{15}\text{N}/^{14}\text{N}_{\text{sample}} - {}^{15}\text{N}/^{14}\text{N}_{\text{standard}}}{{}^{15}\text{N}/^{14}\text{N}_{\text{standard}}} \right) \times 1000 \, \permil where the standard is atmospheric N₂, assigned a value of 0‰ by convention. This per mil (‰) scale allows for precise comparison of isotopic compositions in environmental samples, with typical measurement precision of ±0.2‰ using . In environmental applications, δ¹⁵N serves as a tracer for nutrient sources and transformations in aquatic and terrestrial systems. For instance, elevated δ¹⁵N values greater than +10‰ in or biota often indicate from or , which have characteristically high ratios due to volatilization and microbial processing, whereas synthetic fertilizers typically exhibit lower values near 0‰ to +4‰. processes further enrich residual in ¹⁵N, with factors leading to increases of several per mil, enabling identification of microbial nitrogen loss in and . Geochemical cycles of nitrogen involve isotopic fractionation at various steps, such as during atmospheric processing where Rayleigh distillation enriches the residual gas in ¹⁵N by up to 1-1.5‰ due to kinetic effects in denitrification and photolysis. In paleoclimate records, δ¹⁵N variations in ice cores from and reflect past temperature changes through thermal fractionation in the firn layer, with shifts of several per mil over glacial-interglacial cycles spanning millennia; for example, lower δ¹⁵N during colder periods indicates reduced lock-in depths and altered gas trapping dynamics. Anthropogenic impacts are evident in distinct δ¹⁵N signatures, such as the lower values from runoff altering watershed compositions compared to natural baselines. In marine sediments, low δ¹⁵N ratios (as low as -3‰) during ocean anoxic events like OAE 2 (~94 Ma) trace enhanced N₂ fixation under low-oxygen conditions, with regional variations reflecting and nutrient recycling in the proto-North Atlantic. Recent studies in the 2020s highlight effects on δ¹⁵N in ecosystems, where retreating tidewater glaciers increase freshwater discharge and alter nitrate sources, leading to δ¹⁵N depletion in rivers due to enhanced terrestrial inputs. Advancements in , including Orbitrap-based methods for compound-specific analysis, have improved precision to 3-8‰ for low-abundance samples like , complementing traditional isotope ratio 's ±0.2‰ accuracy for bulk environmental tracing.

References

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