Cobalt bomb

A cobalt bomb, a type of salted bomb, is a form of nuclear weapon originally proposed by physicist Leó Szilárd, who suggested that it would be capable of destroying all life on Earth. The weapon's tamper would be made of ordinary cobalt metal, rather than a fissionable material like depleted uranium. This would be transmuted into the isotope cobalt-60 upon initiation and bombardment by neutron radiation. ⁶⁰Co is a very strong emitter of gamma rays as it undergoes beta decay, and has historically been used for beneficial purposes in radiation therapy.

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Weapon of global destruction

See also: Doomsday device

The fallout would have a half-life of 5.27 years and would be intensely radioactive, a combination which caused Szilárd to suggest that such bombs could wipe out all life on the planet. One gram of ⁶⁰Co contains approximately fifty curies (1.85 terabecquerels) of radioactivity. Held at close range, this amount of cobalt-60 would irradiate a person with approximately 0.5 gray of ionizing radiation per minute. A prompt, full body dose of approximately three to four grays would kill 50% of the population in thirty days, and could be accumulated in just a few minutes of exposure to a gram of ⁶⁰Co.

Smaller amounts of ⁶⁰Co would take longer to kill, but would be effective over a large area. Even so, critics of the cobalt bomb concept point out that the mass needed would still be unreasonably large: 1 gram of ⁶⁰Co per square kilometer of Earth's surface is 510 tonnes. The sheer size and cost of such a weapon makes it unlikely to be built, although it is technically possible because there is no maximum size limit for a thermonuclear bomb.

What is unusual about this type of bomb is that the half-life is long enough to settle out before significant decay has occurred, and to make it impractical to wait out in shelters, yet is short enough that intense radiation is produced. After fifteen to twenty years, the ⁶⁰Co radiation would decrease by a factor of eight to sixteen, presumably making the area habitable again. The ⁶⁰Co would have decayed to stable, and thus harmless, ⁶⁰Ni.

Cobalt bombs in the media

Fiction

Inspired by Szilárd's warnings, science fiction authors have occasionally made cobalt bombs the doomsday weapons in their works:

• The Sum of All Fears by Tom Clancy describes wrapping the bomb on the plane in a cobalt jacket to poison the enemy's landscape.
• On the Beach by Nevil Shute is one of the best known of the fictional stories dealing with cobalt bombs.
• The movie Dr. Strangelove (released Jan, 29, 1964) by Stanley Kubrick describes the Soviet Union building a cobalt/thorium-G bomb.
• Perhaps following the Strangelove reference, the movie Goldfinger (first released September 1964) features a Chinese "atomic device" which is "small, but particularly dirty." James Bond surmises that this device uses "cobalt and iodine" to irradiate the gold at Fort Knox for "57 years" (Goldfinger corrects him to 58 years).
• The film Beneath the Planet of the Apes, the first sequel to the film Planet of the Apes, includes a group of oddly mutated humans living in an underground city within the ruins of the New York Subway system that worship an Alpha-Omega bomb, a nuclear weapon with a cobalt casing that is capable of causing a chain reaction that would (supposedly) incinerate the entire Earth's atmosphere. The final voice-over in the film indicates that it was successful, as does the next film in the series, Escape from the Planet of the Apes..
• In A Taste of Armageddon, a first-season episode of Star Trek: The Original Series, a minor character refers to the use of "tri-cobalt devices" as the primary weapons of both sides in an interplanetary war.
• The Marvel comic character Cobalt Man (created April, 1967) uses a nuclear powered exoskeleton.
• The movie City of Fear (released Feb, 1959).
• The original The Bionic Woman had a two part episode entitled "Doomsday is Tomorrow" where a doomsday device was created by a person who was credited as being the "father of the cobalt bomb."
• Adventure Comics #250 published by DC Comics featured Superboy deputized to track down a criminal from the future seeking materials to make an outlawed cobalt bomb.

Games

• The Damocles, a unique starship found in the computer game Weird Worlds: Return to Infinite Space, is armed with "Cobalt Thorium G" torpedoes.

News

The United Kingdom reputedly conducted a nuclear experiment involving cobalt as a radioactive tracer in 1957, at the Tadje site, Maralinga range, Australia, but it was announced to be a failure ^[1].

In the twenty-first century, new attention came to ⁶⁰Co as a weapon of mass destruction, as the possibility of creating a dirty bomb to disperse this material might produce a swath of death downwind from it, over a significant area, as a terrorist attack. This is simpler than an actual nuclear weapon cobalt bomb, with a smaller range, though it is suggested that it could kill tens of thousands of people in a dense urban area ^[2].

Notes