By Ron B. Davis Jr., Georgetown University
Cobalt’s most speculative use comes from 1950, when a Manhattan Project physicist, named Leo Szilard, attempting to anticipate the worst, suggested it might be possible to build a doomsday nuclear device capable of wiping the human race from the Earth. Surprisingly, the key element suggested for possible use in his warning wasn’t uranium or plutonium, but cobalt.
Leo Szilard
During a round-table discussion, Szilard proposed that wiping human society off the map might just be possible if the radioactive fallout from hydrogen bombs was not thought of as an unfortunate side effect, but instead as a feature of the weapon itself.
The fact is that cobalt-59 is a stable isotope of cobalt that can easily be included in the construction of a thermonuclear device. Its presence would not contribute to the explosive yield in any meaningful way, yet it could increase the bombs death toll by orders of magnitude.
A Nuclear Fallout
This is because the neutron flux—free neutrons released during a nuclear explosion, could convert the cobalt-59 into cobalt-60 through neutron capture.
A giant cloud of cobalt-60 fallout would pose a major health risk to everyone on the planet. This is owing to the fact that cobalt-60 undergoes a beta decay with accompanying gamma radiation, to form the stable isotope, nickel-60.
All nuclear fallout is radioactive, but there are two features of cobalt’s decay that make it especially terrifying.
Emitting Deadly Radiation for Decades
To begin with, cobalt-60 releases high energy gamma radiation as it decays. It is worth noting here that gamma rays are extremely high energy photons that can penetrate deeply, and can be dangerous even when the exposure comes from an external source.
In addition, with a half-life of 5.27 years, the cobalt-60 created and dispersed in a salted bomb explosion is long-lived enough for air currents to distribute it around the globe, emitting deadly radiation for decades—but short enough that the radiation emitted would still have the intensity to be potentially fatal.
Though never constructed or tested, Szilard’s grim thought experiment has inspired references to such a ‘cobalt bomb’ in popular culture.
In the 1964 dark comedy, Dr. Strangelove, such a doomsday device is used as a nuclear deterrent. In another 1964 film, Goldfinger, the antagonist plans to use a smaller cobalt device to poison the American gold supply, at Fort Knox, with radiation. And Tom Clancy, in his 1991 novel, The Sum of All Fears, noted that cobalt jackets might be fitted to nuclear weapons to ‘poison a landscape’ in the years after its detonation.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Goblins and the Devil
Nevertheless, when it comes to the toxicity of cobalt, to be fair, it isn’t all bad. For all of the bad press cobalt has gotten over the years about mining hazards and doomsday devices, the element cobalt itself truly has been a useful and valuable commodity in many other ways. Cobalt has been used in aircraft alloys, class coloring, radiological medicines and magnet production.
Interestingly, Cobalt and nickel get their names from German terms referring to goblins and the devil. These unusual namesakes were given by German miners, who would often mistake ores of cobalt and nickel for those of their more valuable neighbors one column further right on the table, copper and silver.
Reacts with Oxygen
Many of the metallic elements can be isolated as pure metals with a bit of effort. However, considered in the strictest sense, a pure sample of those metals is rarely what nature offers us.
For many metals—including magnesium, aluminum, zinc, bismuth and even the transition metals vanadium and chromium—we have to work to extract the metal from compounds to obtain them in their pure forms.
The reason that these metals, including cobalt, prove so durable is that, even when isolated, the outermost atoms of the element promptly react with oxygen and other components of the air to form a hard, passivating layer that protects the metal beneath.
The Good Properties
Hence, in conclusion, one can say that Cobalt does have some unique properties that are noteworthy. It is used in electrical vehicle batteries helped propel them to their current capabilities that compete with gas and diesel vehicles. However, the toxicity of cobalt, together with human-rights issues surrounding its mining in the few countries with commercially viable deposits, make cobalt a less-than-ideal material for long-term use.
Understandably, for business, environmental, and humanitarian reasons, the search is on for a replacement technology that can offer cobalt’s good properties.
Common Questions about the Cobalt Bomb, Leo Szilard’s Grim Thought Experiment
Cobalt-59 is a stable isotope of cobalt that can easily be included in the construction of a thermonuclear device. Its presence would not contribute to explosive yield in any meaningful way, yet it could increase the bombs death toll by orders of magnitude.
A giant cloud of cobalt-60 fallout would pose a major health risk to everyone on the planet. This is owing to the fact that cobalt-60 undergoes a beta decay with accompanying gamma radiation, to form the stable isotope, nickel-60.
The reason that metals such as cobalt prove so durable is that, even when isolated, the outermost atoms of the element promptly react with oxygen and other components of the air to form a hard, passivating layer that protects the metal beneath.
