From Wikipedia, the free encyclopedia
Krypton-85, 85Kr
Nameskrypton-85, 85Kr, Kr-85
Protons (Z)36
Neutrons (N)49
Nuclide data
Half-life (t1/2)10.756 years
Isotope mass84.9125273(21) Da
Excess energy−81480.267 keV
Binding energy8698.562 keV
Decay products85Rb
Decay modes
Decay modeDecay energy (MeV)
Beta decay0.687
Beta decay0.173
Isotopes of krypton
Complete table of nuclides

Krypton-85 (85Kr) is a radioisotope of krypton.

Krypton-85 has a half-life of 10.756 years and a maximum decay energy of 687 keV.[1] It decays into stable rubidium-85. Its most common decay (99.57%) is by beta particle emission with maximum energy of 687 keV and an average energy of 251 keV. The second most common decay (0.43%) is by beta particle emission (maximum energy of 173 keV) followed by gamma ray emission (energy of 514 keV).[2] Other decay modes have very small probabilities and emit less energetic gamma rays.[1][3] Krypton-85 is mostly synthetic, though it is produced naturally in trace quantities by cosmic ray spallation.

In terms of radiotoxicity, 440 Bq of 85Kr is equivalent to 1 Bq of radon-222, without considering the rest of the radon decay chain.

Presence in Earth's atmosphere[edit]

fission products [further explanation needed]
155Eu 4.76 0.0803 252 βγ
85Kr 10.76 0.2180 687 βγ
113mCd 14.1 0.0008 316 β
90Sr 28.9 4.505   2826 β
137Cs 30.23 6.337   1176 βγ
121mSn 43.9 0.00005 390 βγ
151Sm 88.8 0.5314 77 β

Natural production[edit]

Krypton-85 is produced in small quantities by the interaction of cosmic rays with stable krypton-84 in the atmosphere. Natural sources maintain an equilibrium inventory of about 0.09 PBq in the atmosphere.[4]

Anthropogenic production[edit]

As of 2009 the total amount in the atmosphere is estimated at 5500 PBq due to anthropogenic sources.[5] At the end of the year 2000, it was estimated to be 4800 PBq,[4] and in 1973, an estimated 1961 PBq (53 megacuries).[6] The most important of these human sources is nuclear fuel reprocessing, as krypton-85 is one of the seven common medium-lived fission products.[4][5][6] Nuclear fission produces about three atoms of krypton-85 for every 1000 fissions (i.e., it has a fission yield of 0.3%).[7] Most or all of this krypton-85 is retained in the spent nuclear fuel rods; spent fuel on discharge from a reactor contains between 0.13–1.8 PBq/Mg of krypton-85.[4] Some of this spent fuel is reprocessed. Current nuclear reprocessing releases the gaseous 85Kr into the atmosphere when the spent fuel is dissolved. It would be possible in principle to capture and store this krypton gas as nuclear waste or for use. The cumulative global amount of krypton-85 released from reprocessing activity has been estimated as 10,600 PBq as of 2000.[4] The global inventory noted above is smaller than this amount due to radioactive decay; a smaller fraction is dissolved into the deep oceans.[4]

Other man-made sources are small contributors to the total. Atmospheric nuclear weapons tests released an estimated 111–185 PBq.[4] The 1979 accident at the Three Mile Island nuclear power plant released about 1.6 PBq (43 kCi).[8] The Chernobyl accident released about 35 PBq,[4][5] and the Fukushima Daiichi accident released an estimated 44–84 PBq.[9]

The average atmospheric concentration of krypton-85 was approximately 0.6 Bq/m3 in 1976, and has increased to approximately 1.3 Bq/m3 as of 2005.[4][10] These are approximate global average values; concentrations are higher locally around nuclear reprocessing facilities, and are generally higher in the northern hemisphere than in the southern hemisphere.

For wide-area atmospheric monitoring, krypton-85 is the best indicator for clandestine plutonium separations.[11]

Krypton-85 releases increase the electrical conductivity of atmospheric air. Meteorological effects are expected to be stronger closer to the source of the emissions.[12]

Uses in industry[edit]

Krypton-85 is used in arc discharge lamps commonly used in the entertainment industry for large HMI film lights as well as high-intensity discharge lamps.[13][14][15][16][17] The presence of krypton-85 in discharge tube of the lamps can make the lamps easy to ignite.[14] Early experimental krypton-85 lighting developments included a railroad signal light designed in 1957[18] and an illuminated highway sign erected in Arizona in 1969.[19] A 60 μCi (2.22 MBq) capsule of krypton-85 was used by the random number server HotBits (an allusion to the radioactive element being a quantum mechanical source of entropy), but was replaced with a 5 μCi (185 kBq) Cs-137 source in 1998.[20][21]

Krypton-85 is also used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging".[22] The gas penetrates smaller openings than the liquids used in dye penetrant inspection and fluorescent penetrant inspection.[23]

Krypton-85 was used in cold-cathode voltage regulator electron tubes, such as the type 5651.[24]

Krypton-85 is also used for Industrial Process Control mainly for thickness and density measurements as an alternative to Sr-90 or Cs-137.[25][26]

Krypton-85 is also used as a charge neutralizer in aerosol sampling systems.[27]


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  6. ^ a b Telegadas, K.; Ferber, G. J. (1975-11-28). "Atmospheric Concentrations and Inventory of Krypton-85 in 1973". Science. 190 (4217). American Association for the Advancement of Science: 882–883. Bibcode:1975Sci...190..882T. doi:10.1126/science.190.4217.882. JSTOR 1741777. S2CID 129885789.
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  8. ^ "U.S. NRC: Backgrounder on the Three Mile Island accident". U.S. Nuclear Regulatory Commission. 2014-12-12. Retrieved 2015-05-31.
  9. ^ W. Lin; et al. (2015). "Radioactivity impacts of the Fukushima Nuclear Accident on the atmosphere". Atmospheric Environment. 102: 311–322. Bibcode:2015AtmEn.102..311L. doi:10.1016/j.atmosenv.2014.11.047.
  10. ^ O. Ross; et al. Simulations of the atmospheric krypton-85 to assess the detectability of clandestine nuclear reprocessing (PDF). Symposium on International Safeguards: Preparing for Future Verification Challenges; Vienna (Austria); 1-5 Nov 2010 (Technical report). IAEA-CN-184.
  11. ^ Kalinowski, Martin B.; Sartorius, Hartmut; Uhl, Stefan; Weiss, Wolfgang (2004), "Conclusions on plutonium separation from atmospheric krypton-85 measured at various distances from the Karlsruhe reprocessing plant", Journal of Environmental Radioactivity, 73 (2): 203–22, Bibcode:2004JEnvR..73..203K, doi:10.1016/j.jenvrad.2003.09.002, PMID 15023448
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  13. ^ Krypton-85 (PDF). (2004-12-30). Retrieved on 2013-07-25.
  14. ^ a b Lamp Types, European Lamp Companies Federation, archived from the original on 2012-06-22, retrieved 2012-11-06
  15. ^ Ionizing Substances in Lighting Products (PDF), European Lamp Companies Federation, 2009, archived from the original (PDF) on 2014-02-20, retrieved 2012-11-06
  16. ^ NRPB and GRS (2001), Transport of Consumer Goods containing Small Quantities of Radioactive Materials (PDF), European Commission, archived from the original (PDF) on 2011-11-25, retrieved 2012-11-06
  17. ^ Assessment of the Radiological Impact of the Transport and Disposal of Light Bulbs Containing Tritium, Krypton-85 and Radioisotopes of Thorium, Health Protection Agency, 2011, archived from the original on 2012-05-28, retrieved 2012-11-06
  18. ^ "Make A-powered Rail Signal Light in D&RGW Labs". The Ogden Standard-Examiner. 1957-02-17. Retrieved 2015-05-31 – via
  19. ^ Davis, Al (1970-01-04). "Atomic sign glows day and night here". Arizona Republic. Retrieved 2015-05-31 – via
  20. ^ "Totally Random". Wired Magazine. Vol. 11, no. 8. August 2003.
  21. ^ Walker, John (September 2006). "HotBits Hardware". HotBits.
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  24. ^ 5651 Sylvania Voltage Regulator Stabilizer Electron Tube. (2013-05-15). Retrieved on 2013-07-25.
  25. ^ Krypton-85 (Kr-85) Sealed Sources for Industrial Process Control Retrieved on 2021-09-10
  26. ^ [1] Sealed Sources for Industrial Gauging. M85K01 Series Kr-85 Beta Sources (PDF) Retrieved on 2021-09-10
  27. ^ Liu, Benjamin; Piu, David (1974). "Electrical neutralization of aerosols". Journal of Aerosol Science. 5 (5): 465–472. Bibcode:1974JAerS...5..465L. doi:10.1016/0021-8502(74)90086-X. Retrieved 2023-01-04.