Editing X-ray (section)

===Production in lightning and laboratory discharges===
X-rays are also produced in lightning accompanying [[terrestrial gamma-ray flash]]es. The underlying mechanism is the acceleration of electrons in lightning related electric fields and the subsequent production of photons through ''Bremsstrahlung''.<ref>{{cite journal |last1=Köhn |first1=Christoph |last2=Ebert |first2=Ute |title=Angular distribution of Bremsstrahlung photons and of positrons for calculations of terrestrial gamma-ray flashes and positron beams |journal=Atmospheric Research |date=January 2014 |volume=135-136 |pages=432–465 |doi=10.1016/j.atmosres.2013.03.012 |arxiv=1202.4879 |bibcode=2014AtmRe.135..432K }}</ref> This produces photons with energies of some few [[electronvolt|keV]] and several tens of MeV.<ref>{{cite journal |last1=Köhn |first1=Christoph |last2=Ebert |first2=Ute |title=Calculation of beams of positrons, neutrons, and protons associated with terrestrial gamma ray flashes |journal=Journal of Geophysical Research: Atmospheres |date=27 February 2015 |volume=120 |issue=4 |pages=1620–1635 |doi=10.1002/2014JD022229 |bibcode=2015JGRD..120.1620K |url=https://ir.cwi.nl/pub/23845 }}</ref> In laboratory discharges with a gap size of approximately 1&nbsp;meter length and a peak voltage of 1&nbsp;MV, X-rays with a characteristic energy of 160&nbsp;keV are observed.<ref>{{cite journal |last1=Kochkin |first1=Pavlo |last2=Köhn |first2=Christoph |last3=Ebert |first3=Ute |last4=van Deursen |first4=Lex |title=Analyzing x-ray emissions from meter-scale negative discharges in ambient air |journal=Plasma Sources Science and Technology |date=August 2016 |volume=25 |issue=4 |pages=044002 |doi=10.1088/0963-0252/25/4/044002 |bibcode=2016PSST...25d4002K |url=https://pure.tue.nl/ws/files/45766610/Kochkin_2016_Plasma_Sources_Sci._Technol._25_044002.pdf }}</ref> A possible explanation is the encounter of two [[streamer discharge|streamers]] and the production of high-energy [[Runaway electrons|run-away electrons]];<ref>{{Cite journal |vauthors = Cooray V, Arevalo L, Rahman M, Dwyer J, Rassoul H |doi = 10.1016/j.jastp.2009.07.010 |title = On the possible origin of X-rays in long laboratory sparks |journal = Journal of Atmospheric and Solar-Terrestrial Physics |volume = 71 |issue = 17–18 |pages = 1890–1898 |date= 2009 |bibcode = 2009JASTP..71.1890C}}</ref> however, microscopic simulations have shown that the duration of electric field enhancement between two streamers is too short to produce a significant number of run-away electrons.<ref>{{cite journal |vauthors = Köhn C, Chanrion O, Neubert T |title = Electron acceleration during streamer collisions in air |journal = Geophysical Research Letters |volume = 44 |issue = 5 |pages = 2604–2613 |date = March 2017 |pmid = 28503005 |pmc = 5405581 |doi = 10.1002/2016GL072216 |bibcode = 2017GeoRL..44.2604K }}</ref> Recently, it has been proposed that air perturbations in the vicinity of streamers can facilitate the production of run-away electrons and hence of X-rays from discharges.<ref>{{Cite journal |vauthors = Köhn C, Chanrion O, Babich LP, Neubert T |doi = 10.1088/1361-6595/aaa5d8 |title = Streamer properties and associated x-rays in perturbed air |journal = Plasma Sources Science and Technology |volume = 27 |pages = 015017 |date= 2018 |issue = 1 |bibcode = 2018PSST...27a5017K |doi-access = free}}</ref><ref>{{cite journal |vauthors = Köhn C, Chanrion O, Neubert T |title = High-Energy Emissions Induced by Air Density Fluctuations of Discharges |journal = Geophysical Research Letters |volume = 45 |issue = 10 |pages = 5194–5203 |date = May 2018 |pmid = 30034044 |pmc = 6049893 |doi = 10.1029/2018GL077788 |bibcode = 2018GeoRL..45.5194K }}</ref>