Editing Cosmic ray (section)

==Composition==
Of primary cosmic rays, which originate outside of Earth's atmosphere, about 99% are the bare nuclei of common atoms (stripped of their electron shells), and about 1% are solitary electrons (that is, one type of [[beta particle]]). Of the nuclei, about 90% are simple [[proton]]s (i.e., hydrogen nuclei); 9% are [[alpha particle]]s, identical to helium nuclei; and 1% are the nuclei of heavier elements, called [[HZE ions]].<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> These fractions vary highly over the energy range of cosmic rays.<ref name=dembinski-2017>{{cite journal|author1=Dembinski, H.|display-authors=etal|year=2018|title=Data-driven model of the cosmic-ray flux and mass composition from 10 GeV to 10^11 GeV|journal=[[Proceedings of Science]]|volume=ICRC2017|page=533|doi=10.22323/1.301.0533|arxiv=1711.11432|s2cid=85540966 |doi-access=free }}</ref> A very small fraction are stable particles of [[antimatter]], such as [[positron]]s or [[antiproton]]s. The precise nature of this remaining fraction is an area of active research. An active search from Earth orbit for [[Alpha particle#Anti-alpha particle|anti-alpha particles]] as of 2019<ref>{{cite web|title=Cosmic Rays|series=Science Toolbox|website=imagine.gsfc.nasa.gov|publisher=[[National Aeronautics and Space Administration]]|department=Goddard Space Flight Center|url=https://imagine.gsfc.nasa.gov/science/toolbox/cosmic_rays1.html|access-date=23 March 2019}}</ref> had found no unequivocal evidence.

Upon striking the atmosphere, cosmic rays violently burst atoms into other bits of matter, producing large amounts of [[pion]]s and [[muon]]s (produced from the decay of charged pions, which have a short half-life) as well as [[neutrino]]s.<ref name="Vox">{{cite web | last = Resnick | first = Brian | title = Extremely powerful cosmic rays are raining down on us. No one knows where they come from | publisher = [[Vox Media]]   | date = July 25, 2019 | url = https://www.vox.com/the-highlight/2019/7/16/17690740/cosmic-rays-universe-theory-science | accessdate = 2022-12-14 }}</ref> The [[neutron]] composition of the particle cascade increases at lower elevations, reaching between 40% and 80% of the radiation at aircraft altitudes.<ref name="pmid32975102">{{cite journal | vauthors= Sovilj MP, Vuković B, Stanić D | title=Potential benefit of retrospective use of neutron monitors in improving ionising radiation exposure assessment on international flights: issues raised by neutron passive dosimeter measurements and EPCARD simulations during sudden changes in solar activity | journal=Arhiv Za Higijenu Rada I Toksikologiju | volume=71 | issue=2|  pages=152–157 | year=2020  | doi = 10.2478/aiht-2020-71-3403 | pmc=7968484 | pmid=32975102}}</ref>

Of secondary cosmic rays, the charged pions produced by primary cosmic rays in the atmosphere swiftly decay, emitting muons. Unlike pions, these muons do not interact strongly with matter, and can travel through the atmosphere to penetrate even below ground level. The rate of muons arriving at the surface of the Earth is such that about one per second passes through a volume the size of a person's head.<ref>CERN https://home.cern/science/physics/cosmic-rays-particles-outer-space</ref> Together with natural local radioactivity, these muons are a significant cause of the ground level atmospheric ionisation that first attracted the attention of scientists, leading to the eventual discovery of the primary cosmic rays arriving from beyond our atmosphere.