Editing Proton (section)

==Occurrence==
One or more bound protons are present in the nucleus of every atom.
Free protons are found naturally in a number of situations in which energies or temperatures are high enough to separate them from electrons, for which they have some affinity. Free protons exist in [[plasma (physics)|plasmas]] in which temperatures are too high to allow them to combine with [[electron]]s.<ref name=Ebeling2021>{{cite journal |title=Equation of state of hydrogen, helium, and solar plasmas |first1=W. |last1=Ebeling |first2=H. |last2=Reinholz |first3=G. |last3=Röpke |date=2021 |journal=Contributions to Plasma Physics |volume=61 |issue=10 |doi=10.1002/ctpp.202100085|bibcode=2021CoPP...61E0085E }}</ref> Free protons of high energy and velocity make up 90% of [[cosmic ray]]s, which propagate through the [[interstellar medium]].<ref name=goddard-2012>{{cite web|title=What are cosmic rays?|publisher=NASA|department=Goddard Space Flight Center|url=http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html|access-date=31 October 2012|url-status=dead|archive-url=https://web.archive.org/web/20121028154200/http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html|archive-date=28 October 2012}}{{cite web|title=mirror copy, also archived|url=http://certificate.ulo.ucl.ac.uk/modules/year_one/NASA_GSFC/goddard/imagine.gsfc.nasa.gov/docs/science/know_l2/cosmic_rays.html|archive-url=https://web.archive.org/web/20160304080140/http://certificate.ulo.ucl.ac.uk/modules/year_one/NASA_GSFC/goddard/imagine.gsfc.nasa.gov/docs/science/know_l2/cosmic_rays.html|archive-date=4 March 2016}}
</ref> Free protons are [[proton emission|emitted directly]] from [[atomic nucleus|atomic nuclei]] in some rare types of [[radioactive decay]].<ref>{{Cite book |url=http://link.springer.com/10.1007/978-94-010-0708-5 |title=Nuclei Far from Stability and Astrophysics |publisher=Springer Netherlands |year=2001 |isbn=978-0-7923-6937-0 |editor-last=Poenaru |editor-first=Dorin N. |location= Dordrecht |pages=79–81 |language=English |doi=10.1007/978-94-010-0708-5 |editor-last2=Rebel |editor-first2=Heinigerd |editor-last3=Wentz |editor-first3=Jürgen}}</ref> Protons also result (along with electrons and [[antineutrino]]s) from the [[free neutron decay|radioactive decay of free neutrons]], which are unstable.<ref name=Gonzalez-2021>{{Cite journal|last1=UCNτ Collaboration|last2=Gonzalez|first2=F. M.|last3=Fries|first3=E. M.|last4=Cude-Woods|first4=C.|last5=Bailey|first5=T.|last6=Blatnik|first6=M.|last7=Broussard|first7=L. J.|last8=Callahan|first8=N. B.|last9=Choi|first9=J. H.|last10=Clayton|first10=S. M.|last11=Currie|first11=S. A.|date=2021-10-13|title=Improved Neutron Lifetime Measurement with UCNτ|url=https://par.nsf.gov/servlets/purl/10304438|journal=Physical Review Letters|volume=127|issue=16|page=162501|arxiv=2106.10375|doi=10.1103/PhysRevLett.127.162501|pmid=34723594|bibcode=2021PhRvL.127p2501G|s2cid=235490073|access-date=2024-04-01|archive-date=2024-04-01|archive-url=https://web.archive.org/web/20240401134040/https://par.nsf.gov/servlets/purl/10304438|url-status=live}}</ref>