Nitrogen-13

Nitrogen-13 is used in medical PET imaging in the form of ¹³N-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,{{cite journal |last1=Islam |first1=M. R. |last2=Beni |first2=M. S. |last3=Ng |first3=C |display-authors=et al. |date=2022 |title=Proton range monitoring using ¹³N peak for proton therapy applications |journal=PLOS ONE |volume=17 |issue=2 |pages=e0263521-1–e0263521-18 |doi=10.1371/journal.pone.0263521|pmid=35167589 |doi-access=free |pmc=8846528 }} as it is endothermic (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 extra energy to induce the nuclear reaction.

The energy difference is actually 5.22 MeV, but if the proton only supplied this energy, the reactants would be formed with no kinetic energy. As momentum must be conserved, the true energy that needs to be supplied by the proton is given by:

:$K\; =(1+m/M)\; |E|$

where $m$ is the mass of ⁴He and $M$ is the mass of ¹³N ; therefore {{nowrap|$m/M\; \backslash approx\; 0.308$}}. 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 producing ¹³N-labelled ammonia exist, some of which facilitate co-generation of other light radionuclides for diagnostic imaging.{{cite web | last1=Biricova | first1=Veronika | last2=Kuruc | first2= Jozef | title=Synthesis of the radiopharmaceuticals for positron emission tomography | url=https://www.osti.gov/etdeweb/servlets/purl/20895812 | date=2007 | publisher=U.S. Department of Energy, Office of Scientific and Technical Information | access-date=4 August 2022}}{{cite journal | journal=EJNMMI Radiopharm Chem. | volume=5 | issue=11 | doi=10.1186/s41181-020-00097-7 | date=13 May 2020 | pmid=32405797 | last1=Yokell | first1=Daniel L. | last2=Rice |first2=Peter A. | last3=Neelamegam | first3=Ramesh | last4=El Fakhri | first4=Georges | title=Development, validation and regulatory acceptance of improved purification and simplified quality control of [¹³N] Ammonia | page=11 | doi-access=free | pmc=7221112 }}

File:CNO Cycle.svg

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.{{cite book|author=Phillips, A.C. |title=The Physics of Stars |publisher=John Wiley & Sons |year=1994|isbn=0-471-94057-7}}

Lightning may have a role in the production of nitrogen-13.{{cite web |url=https://phys.org/news/2017-11-lightning-chance-antimatter.html |title=Lightning, with a chance of antimatter |last= |first= |date=November 22, 2017 |website=Phys.org |publisher=ScienceX |access-date=November 24, 2017 |quote=The gamma rays emitted in lightning have enough energy to knock a neutron out of atmospheric nitrogen}}{{cite journal |url=https://www.nature.com/news/lightning-makes-new-isotopes-1.23033 |title=Lightning makes new isotopes |last=Castelvecchi|first=Davide |date=November 22, 2017 |journal=Nature |doi=10.1038/nature.2017.23033 |access-date=November 29, 2017 |quote=|url-access=subscription }}

• [https://web.archive.org/web/20110407232812/http://www.petnm.unimelb.edu.au/pet/index.html PET site] of the University of Melbourne

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{{Isotope sequence

|element=nitrogen

|lighter=nitrogen-12

|heavier=nitrogen-14

|before=oxygen-13 (electron capture)

|after=carbon-13 (EC)

}}

Category:Isotopes of nitrogen

Category:Positron emitters

Category:Medical isotopes