Nitrogen-13, ¹³N

General
Symbol	13N
Names	nitrogen-13, 13N, N-13
Protons(Z)	7
Neutrons(N)	6
Nuclide data
Half-life(t1/2)	9.97 min
Parent isotopes	13O (β+)
Decay modes
Decay mode	Decay energy (MeV)
β+	1.2003
Isotopes of nitrogen Complete table of nuclides

Nitrogen-13 (¹³N) is aradioisotope ofnitrogen used inpositron emission tomography (PET). It has ahalf-life of a little under ten minutes, so it must be made at the PET site. Acyclotron may be used for this purpose.

Nitrogen-13 is used to tagammonia molecules for PETmyocardial perfusion imaging.

Nitrogen-13 is used in medical PET imaging in the form of¹³N-labelled ammonia. 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 (present as H₂O) and a proton, and the products are nitrogen-13 and an alpha particle (helium-4).

¹H +¹⁶O →¹³N +⁴He

The proton must be accelerated to have total energy greater than 5.66 MeV. This is the threshold energy for this reaction,^[1] as it isendothermic (i.e., the mass of the products is greater than the reactants, so energy needs to be supplied which is converted to mass). For this reason, the proton needs to carry extraenergy to induce thenuclear reaction.

The energy difference is actually 5.22 MeV, but if the proton only supplied this energy, the reactants would be formed with nokinetic energy. Asmomentum must beconserved, the true energy that needs to be supplied by the proton is given by:

${\displaystyle K=(1+m/M)|E|}$

where${\displaystyle m}$ is the mass of⁴He and${\displaystyle M}$ is the mass of¹³N ; therefore${\displaystyle m/M\approx 0.308}$. The presence of ethanol (at a concentration of ~5mM) in aqueous solution allows the convenient formation of ammonia as nitrogen-13 is produced. Other routes of producing¹³N-labelled ammonia exist, some of which facilitate co-generation of other light radionuclides for diagnostic imaging.^[2][3]

Nitrogen-13 plays a significant role in theCNO cycle, which is the dominant source of energy inmain-sequence stars more massive than 1.5 times themass of theSun.^[4]

Lightning may have a role in the production of nitrogen-13.^[5][6]

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