15N

15N is a stable isotope of nitrogen with mass number 15. It contains 7 protons and 8 neutrons, giving an atomic number of 7. Among nitrogen's stable isotopes, 14N is far more abundant. The natural abundance of 15N in nitrogen-bearing materials is about 0.37%, with the remainder mainly being 14N. Isotopic ratios are commonly expressed as δ15N to characterize nitrogen sources and transformations in environmental and biological systems.

In nature, 15N is produced in stellar nucleosynthesis and is present in Earth's atmosphere as part of nitrogen gas (N2) together with 14N. It is non-radioactive and does not decay over time.

15N is widely used as a stable isotope tracer in biochemistry, agriculture, and environmental science. It is incorporated into amino acids, nucleotides, and other biomolecules to study metabolic pathways. In analytical chemistry, 15N labeling aids detection in mass spectrometry and enables quantitative isotope tracing. In nuclear magnetic resonance spectroscopy, 15N has nuclear spin I = 1/2, unlike 14N which has I = 1, a property that makes 15N NMR particularly useful for studying proteins, nucleic acids, and other labeled samples.

Because it is stable, 15N does not pose radiological hazards. Production of enriched 15N for research uses isotope separation techniques such as fractional distillation of nitrogen gas or chemical exchange methods.