Isotopes of nitrogen
Natural nitrogen consists of two stable isotopes: the vast majority of naturally occurring nitrogen is nitrogen-14, with the remainder 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
Nitrogen-13
Nitrogen-13 has a half-life of a little under ten minutes. It is produced in the atmosphere when gamma rays knock neutrons out of nitrogen-14.13N decays to 13C, emitting a positron. The positron quickly annihilates with an electron, producing two gamma rays of about. 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.
Nitrogen-13 plays a significant role in the CNO cycle, which is the dominant source of energy in main sequence stars more massive than 1.5 times the mass of the Sun.
Nitrogen-13 is used in positron emission tomography in the form of 13N-labelled ammonia, for example for myocardial perfusion imaging. It can be produced with a medical cyclotron, using a target of pure water with a trace amount of ethanol. The reactants are oxygen-16 and a proton, and the products are nitrogen-13 and an alpha particle :
In this endothermic reaction, the proton must be accelerated to have a total energy greater than 5.66 MeV. The presence of ethanol allows the formation of ammonia as nitrogen-13 is produced. Other routes of producing 13N-labelled ammonia exist, some of which facilitate co-generation of other light radionuclides for diagnostic imaging.
Nitrogen-14
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 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.
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.
Nitrogen-15
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.Nitrogen-15 is frequently used in NMR. 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.