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Name, symbol Krypton,85Kr
Neutrons 49
Protons 36
Nuclide data
Half-life 10.756 years
Isotope mass 84.9125273(21) u
Spin 9/2+
Decay mode Decay energy
Beta decay 0.687 MeV
fission products
Q *
βγ *
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 96.6 0.5314 77 β

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

It has a half-life of 10.756 years and a maximum decay energy of 687 keV.[1] It decays into stable, non-radioactive 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 gammas.[1][3] There are 33 other known isotopes of krypton.

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

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]

However, 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.[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 Kr-85 to 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]

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.[12][13][14][15][16] The existence of Kr-85 in discharge tube of the lamps can make the lamps easy to ignite.[13] Early experimental Krypton-85 lighting developments included a railroad signal light designed in 1957[17] and an illuminated highway sign erected in Arizona in 1969.[18]

Krypton-85 is 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". The gas penetrates smaller openings than the liquids used in dye penetrant inspection and fluorescent penetrant inspection.[19]

The sealed spark gap assemblies contained in ignition excitors used in some older turbine/jet engines contain a very small amount of krypton-85 in order to obtain consistent ionization levels and uniform operation. The amount of radiation from the average gap is approximately the same as that of a radium-dial wrist watch but should be handled carefully.

Krypton-85 was used in cold-cathode voltage regulator electron tubes, such as the type 5651.[20]

Krypton-85 is used to test for leaks in semiconductors (MIL-STD-883H) and piping.

Krypton-85 is used to ionizing of spark gap inlet gases for breakdown voltage.

Krypton-85 is used in neutralization of electrostatically charged aerosols from nebulization, combustion, or powder dispersion.

Krypton-85 is also used to measure extruded film or coating weight during online production.

See also[edit]


  1. ^ a b "WWW Table of Radioactive Isotopes - Kr85". Lawrence Berkely Laboratories, USA. Retrieved 2015-05-30. 
  2. ^ M. Gorden; et al. (15 July 2011). "Pinellas Plant – Occupational Environmental Dose rev1" (PDF). ORAU. Retrieved 2015-05-30. 
  3. ^ H. Sievers (1991). "Nuclear data sheets update for A=85". Nuclear Data Sheets 62: 271. doi:10.1016/0090-3752(91)80016-Y. 
  4. ^ a b c d e f g h i K. Winger; et al. (2005). "A new compilation of the atmospheric 85krypton inventories from 1945 to 2000 and its evaluation in a global transport model". Jrnl of Envir Radioactivity 80: 183–215. doi:10.1016/j.jenvrad.2004.09.005. 
  5. ^ a b c J. Ahlswede; et al. (2013). "Update and improvement of the global krypton-85 emission inventory". Jrnl of Envir Radioactivity 115: 34–42. doi:10.1016/j.jenvrad.2012.07.006. 
  6. ^ a b Telegadas, K.; Ferber, G. J. (1975-11-28). "Atmospheric Concentrations and Inventory of Krypton-85 in 1973". Science (American Association for the Advancement of Science). Retrieved 2015-06-01. 
  7. ^ "Cumulative Fission Yields". JEFF-3.1 Nuclear Data Library, JEFF Report 21, OECD/NEA, Paris, France, 2006, ISBN 92-64-02314-3. August 2005. Retrieved 2015-06-01. 
  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. 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, doi:10.1016/j.jenvrad.2003.09.002, PMID 15023448 
  12. ^ Krypton-85 (PDF). (2004-12-30). Retrieved on 2013-07-25.
  13. ^ a b Lamp Types, European Lamp Companies Federation, archived from the original on 2012-11-06, retrieved 2012-11-06 
  14. ^ Ionizing Substances in Lighting Products, European Lamp Companies Federation, 2009, archived from the original (PDF) on 2012-11-06, retrieved 2012-11-06 
  15. ^ NRPB and GRS (2001), Transport of Consumer Goods containing Small Quantities of Radioactive Materials, European Commission, archived from the original (PDF) on 2012-11-06, retrieved 2012-11-06 
  16. ^ 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 2012-11-06, retrieved 2012-11-06 
  17. ^ "Make A-powered Rail Signal Light in D&RGW Labs". The Ogden Standard-Examiner. 1957-02-17. Retrieved 2015-05-31 – via 
  18. ^ Davis, Al (1970-01-04). "Atomic sign glows day and night here". Arizona Republic. Retrieved 2015-05-31 – via 
  19. ^ Glatz, Joseph. Krypton Gas Penetrant Imaging – A Valuable Tool for Ensuring Structural Integrity in Aircraft Engine Components. American Society for Nondestructive Testing
  20. ^ 5651 Sylvania Voltage Regulator Stabilizer Electron Tube. (2013-05-15). Retrieved on 2013-07-25.