A cobalt bomb is a type of "salted bomb": a nuclear weapon designed to produce enhanced amounts of radioactive fallout, intended to contaminate a large area with radioactive material, potentially for the purpose of radiological warfare, mutual assured destruction or as doomsday devices. There is no firm evidence that such a device has ever been built or tested.


The concept of a cobalt bomb was originally described in a radio program by physicist Leó Szilárd on February 26, 1950.[1] His intent was not to propose that such a weapon be built, but to show that nuclear weapon technology would soon reach the point where a doomsday device could end human life on Earth.[2][3]

The Operation Antler/Round 1 test by the British at the Tadje site in the Maralinga range in Australia on September 14, 1957, tested a bomb using cobalt pellets as a radiochemical tracer for estimating yield. This was considered a failure and the experiment was not repeated.[4] In Russia, the triple "taiga" nuclear salvo test, as part of the preliminary March 1971 Pechora–Kama Canal project, produced relatively high amounts of cobalt-60 (60Co or Co-60) from the steel that surrounded the Taiga devices, with this fusion-generated neutron activation product being responsible for about half of the gamma dose in 2011 at the test site. The high percentage contribution is largely because the devices primarily used fusion rather than fission reactions, so the quantity of gamma-emitting caesium-137 fallout was comparatively low. Photosynthesizing vegetation exists all around the lake that was formed.[5][6]

In 2015, a page from an apparent Russian nuclear torpedo design was leaked. The design was titled "Oceanic Multipurpose System Status-6", later given the official name Poseidon.[7][8][9][10] The document stated the torpedo would create "wide areas of radioactive contamination, rendering them unusable for military, economic or other activity for a long time." Its payload would be "many tens of megatons in yield". Russian government newspaper Rossiiskaya Gazeta speculated that the warhead would be a cobalt bomb. It is not known whether the Status-6 is a real project, or whether it is Russian disinformation.[11][12] In 2018 the Pentagon's annual Nuclear Posture Review stated Russia is developing a system called the "Status-6 Oceanic Multipurpose System". If Status-6 does exist, it is not publicly known whether the leaked 2015 design is accurate, nor whether the 2015 claim that the torpedo might be a cobalt bomb is genuine.[12] Amongst other comments on it, Edward Moore Geist wrote a paper in which he says that "Russian decision makers would have little confidence that these areas would be in the intended locations"[13] and Russian military experts are cited as saying that "robotic torpedoes could have other purposes, such as delivering deep-sea equipment or installing surveillance devices."[11]


Decay of cobalt-60 showing the release of powerful gamma rays.

A cobalt bomb could be made by placing a quantity of ordinary cobalt metal (59Co) around a thermonuclear bomb. When the bomb explodes, the neutrons produced by the fusion reaction in the secondary stage of the thermonuclear bomb's explosion would transmute the cobalt to the radioactive cobalt-60, which would be vaporized by the explosion. The cobalt would then condense and fall back to Earth with the dust and debris from the explosion, contaminating the ground.

The deposited cobalt-60 would have a half-life of 5.27 years, decaying into 60Ni and emitting two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is:

+ n → 60
+ e + gamma rays.

Nickel-60 is a stable isotope and undergoes no further decays after the transmutation is complete.

The 5.27 year half life of the 60Co is long enough to allow it to settle out before significant decay has occurred, and to render it impractical to wait in shelters for it to decay, yet short enough that intense radiation is produced.[4] Many isotopes are more radioactive (gold-198, tantalum-182, zinc-65, sodium-24, and many more), but they would decay faster, possibly allowing some population to survive in shelters.

Fallout from cobalt bombs in comparison to other nuclear weapons

Fission products are more deadly than neutron-activated cobalt in the first few weeks following detonation. After one to six months, the fission products from even a large-yield thermonuclear weapon decay to levels tolerable by humans. The large-yield two-stage (a fission trigger/primary with a fusion–fission secondary) thermonuclear weapon is thus automatically a weapon of radiological warfare, but its fallout decays much more rapidly than that of a cobalt bomb. A cobalt bomb's fallout on the other hand would render affected areas effectively stuck in this interim state for decades: habitable, but not safe for constant habitation.

Initially, gamma radiation from the fission products of an equivalent size fission-fusion-fission bomb are much more intense than Co-60: 15,000 times more intense at 1 hour; 35 times more intense at 1 week; 5 times more intense at 1 month; and about equal at 6 months. Thereafter fission product fallout radiation levels drop off rapidly, so that Co-60 fallout is 8 times more intense than fission at 1 year and 150 times more intense at 5 years. The very long-lived isotopes produced by fission would overtake the 60Co again after about 75 years.[14]

Complete 100% conversion into Co-60 is unlikely; a 1957 British experiment at Maralinga showed that Co-59's neutron absorption ability was much lower than predicted, resulting in a very limited formation of Co-60 isotope in practice.

In addition, fallout is not deposited evenly throughout the path downwind from a detonation, so some areas would be relatively unaffected by fallout and the Earth would not be universally rendered lifeless by a cobalt bomb.[15] The fallout and devastation following a nuclear detonation does not scale upwards linearly with the explosive yield (equivalent to tons of TNT). As a result, the concept of "overkill"—the idea that one can simply estimate the destruction and fallout created by a thermonuclear weapon of the size postulated by Leo Szilard's "cobalt bomb" thought experiment by extrapolating from the effects of thermonuclear weapons of smaller yields—is fallacious.[16][dubiousdiscuss] However, nuclear devices exploded at high altitudes result in much more widespread but slower fallout, especially for dirty or cobalt-like weapons. The radioactive isotopes are caught in the natural global meteorological processes which, because of the extraordinary hardiness of the isotope, will cycle many times throughout the condensation and evaporation process, resulting in global spread and the effective destruction of usable water for plants, land animals, humans, and sea life.[citation needed]

Example of radiation levels vs. time

For the type of radiation given by a cobalt bomb, the dosage measured in sievert (Sv) and gray (Gy) can be treated as equivalent. This is because the relevant harmful radiation from cobalt-60 is gamma rays. When converting between sievert and gray for gamma rays, the radiation type weighting factor will be 1, and the radiation will be a highly penetrating radiation spread evenly over the body so the tissue type weighting factor will also be 1.

Assume a cobalt bomb deposits intense fallout causing a dose rate of 10 Sv per hour. At this dose rate, any unsheltered person exposed to the fallout would receive a lethal dose in about 30 minutes (assuming a median lethal dose of 5 Sv[17]). People in well-built shelters would be safe due to radiation shielding.


See also: Cactus Dome and Radioactive contamination § Decontamination

It may be possible to decontaminate relatively small areas contaminated by a cobalt bomb with equipment such as excavators and bulldozers covered with lead glass, similar to those employed in the Lake Chagan project.[20] By skimming off the thin layer of fallout on the topsoil surface and burying it in the likes of a deep trench along with isolating it from ground water sources, the gamma air dose is cut by orders of magnitude.[21][22] The decontamination after the Goiânia accident in Brazil in 1987 and the possibility of a "dirty bomb" with Co-60, which has similarities with the environment that one would be faced with after a nuclear yielding cobalt bomb's fallout had settled, has prompted the invention of "Sequestration Coatings" and cheap liquid phase sorbents for Co-60 that would further aid in decontamination, including that of water.[23][24][25]

In popular culture

See also


  1. ^ Clegg, Brian (2012-12-11). Armageddon Science: The Science of Mass Destruction. St. Martins Griffin. p. 77. ISBN 978-1-250-01649-2.
  2. ^ Bhushan, K.; G. Katyal (2002). Nuclear, Biological, and Chemical Warfare. India: APH Publishing. pp. 75–77. ISBN 978-81-7648-312-4.
  3. ^ Sublette, Carey (July 2007). "Types of nuclear weapons". FAQ. The Nuclear Weapon Archive. Retrieved 2010-02-13.
  4. ^ a b "1.6 Cobalt Bombs and other Salted Bombs". Retrieved February 10, 2011.
  5. ^ Ramzaev, V.; Repin, V.; Medvedev, A.; Khramtsov, E.; Timofeeva, M.; Yakovlev, V. (2011). "Radiological investigations at the 'Taiga' nuclear explosion site: Site description and in situ measurements". Journal of Environmental Radioactivity. 102 (7): 672–680. doi:10.1016/j.jenvrad.2011.04.003. PMID 21524834.
  6. ^ Ramzaev, V.; Repin, V.; Medvedev, A.; Khramtsov, E.; Timofeeva, M.; Yakovlev, V. (2012). "Radiological investigations at the 'Taiga' nuclear explosion site, part II: man-made γ-ray emitting radionuclides in the ground and the resultant kerma rate in air". Journal of Environmental Radioactivity. 109: 1–12. doi:10.1016/j.jenvrad.2011.12.009. PMID 22541991.
  7. ^ "U.S. calls for new nuclear weapons as Russia develops nuclear-armed torpedo". USA TODAY. 2018. Retrieved 4 February 2018.
  8. ^ Trevithick, Joseph (2018-07-19). "Russia Releases Videos Offering An Unprecedented Look At Its Six New Super Weapons". The Drive. Retrieved 2021-04-27.
  9. ^ Peck, Michael (2015-12-08). "Russia's New Super-Torpedo Carries the Threat of Nuclear Contamination". The National Interest.
  10. ^ "'Secret' Russian nuclear torpedo blueprint leaked". Fox News. November 12, 2015.
  11. ^ a b "Russia reveals giant nuclear torpedo in state TV 'leak'". BBC News. November 12, 2015. Retrieved February 16, 2017.
  12. ^ a b "Buried In Trump's Nuclear Report: A Russian Doomsday Weapon". NPR.org. 2 February 2018. Retrieved 4 February 2018.
  13. ^ Geist, Edward Moore (July 3, 2016). "Would Russia's undersea "doomsday drone" carry a cobalt bomb?". Bulletin of the Atomic Scientists. 72 (4): 238–242. Bibcode:2016BuAtS..72d.238G. doi:10.1080/00963402.2016.1195199. S2CID 147795467.
  14. ^ "Section 1.0 Types of Nuclear Weapons". nuclearweaponarchive.org.
  15. ^ Glasstone, Samuel; Dolan, Philip J., eds. (1977). "The Effects of Nuclear Weapons" (PDF) (3rd ed.). Washington, D.C.: United States Department of Defense and Department of Energy. Archived (PDF) from the original on 2022-10-09. ((cite journal)): Cite journal requires |journal= (help)
  16. ^ Martinus, Brian (December 1982). "The global health effects of nuclear war". Current Affairs Bulletin. 59 (7): 14–26.
  17. ^ "Lethal dose (LD)". www.nrc.gov. Retrieved 2017-02-12.
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  19. ^ United Nations Scientific Committee on the Effects of Atomic Radiation (2008). Sources and effects of ionizing radiation. New York: United Nations (published 2010). p. 4. ISBN 978-92-1-142274-0. Retrieved 9 November 2012.
  20. ^ Archived at Ghostarchive and the Wayback Machine: Born of Nuclear Blast: Russia's Lakes of Mystery. YouTube. November 28, 2010.
  21. ^ Joint FAO/IAEA Programme. "Joint Division Questions & Answers - Nuclear Emergency Response for Food and Agriculture, NAFA". iaea.org.
  22. ^ International Atomic Energy Agency International Atomic Enmergy Agency, 2000 - Technology & Engineering - restoration of environments with radioactive residues : papers and discussions, 697 pages
  23. ^ "Scavenging cobalt from radwaste". neimagazine.com.
  24. ^ "Sequestration Coating Performance Requirements for Mitigation of Contamination from a Radiological Dispersion Device- 9067" (PDF). Wmsym.org. Archived (PDF) from the original on 2022-10-09. Retrieved 2015-11-12.
  25. ^ Drake, John. "Sequestration Coating Performance Requirements for Mitigation of Contamination from a Radiological Dispersion Device" (PDF). Cfpub.epa.gov. Retrieved 2015-11-12.
  26. ^ Smith, P. D. (25 September 2008). "Doomsday Men: The Real Dr Strangelove and the Dream of the Superweapon". Penguin UK.
  27. ^ Kuberski, Philip (2012). Kubrick's Total Cinema: Philosophical Themes and Formal Qualities. Bloomsbury Publishing USA. ISBN 9781441149565.
  28. ^ "No Mr Bond, I don't know about anything radioactivity". Science by degrees. 2018-02-21. Retrieved 2019-06-11.
  29. ^ "Excerpt from The Sum of All Fears". Penguin Random House Canada. Retrieved 2019-06-11.
  30. ^ Peel, John (1991). "Timewyrm: Genesis". The Internet Archive. Retrieved 2022-12-01.