A salted bomb is a nuclear weapon designed to function as a radiological weapon, producing enhanced quantities of radioactive fallout, rendering a large area uninhabitable. The term is derived both from the means of their manufacture, which involves the incorporation of additional elements to a standard atomic weapon, and from the expression "to salt the earth", meaning to render an area uninhabitable for generations. The idea originated with Hungarian-American physicist Leo Szilard, in February 1950. 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 it could end human life on Earth.
No intentionally salted bomb has ever been atmospherically tested, and as far as is publicly known, none have ever been built. However, the UK tested a 1 kiloton bomb incorporating a small amount of cobalt as an experimental radiochemical tracer at their Tadje testing site in Maralinga range, Australia, on September 14, 1957. The triple "taiga" nuclear salvo test, as part of the preliminary March 1971 Pechora–Kama Canal project, converted significant amounts of stable cobalt-59 to radioactive cobalt-60 by fusion generated neutron activation and this product is responsible for about half of the gamma dose measured at the test site in 2011. The experiment was regarded as a failure and not repeated.
A salted bomb should not be confused with a dirty bomb, which is an ordinary explosive bomb containing radioactive material which is spread over the area when the bomb explodes. A salted bomb is able to contaminate a much larger area than a dirty bomb.
Salted versions of both fission and fusion weapons can be made by surrounding the core of the explosive device with a material containing an element that can be converted to a highly radioactive isotope by neutron bombardment. When the bomb explodes, the element absorbs neutrons released by the nuclear reaction, converting it to its radioactive form. The explosion scatters the resulting radioactive material over a wide area, leaving it uninhabitable far longer than an area affected by typical nuclear weapons. In a salted hydrogen bomb, the radiation case around the fusion fuel, which normally is made of some fissionable element, is replaced with a metallic salting element. Salted fission bombs can be made by replacing the neutron reflector between the fissionable core and the explosive layer with a metallic element. The energy yield from a salted weapon is usually lower than from an ordinary weapon of similar size as a consequence of these changes.
The radioactive isotope used for the fallout material would be a high intensity gamma ray emitter, with a half-life long enough that it remains lethal for an extended period. It would also have to have a chemistry that causes it to return to earth as fallout, rather than stay in the atmosphere after being vaporized in the explosion. Another consideration is biological: radioactive isotopes of elements normally taken up by animals as nutrition would pose a special threat to organisms that absorbed them, as their radiation would be delivered from within the body of the organism.
Radioactive isotopes that have been suggested for salted bombs include gold-198, tantalum-182, zinc-65, and cobalt-60. Physicist W. H. Clark looked at the potential of such devices and estimated that a 20 megaton bomb salted with sodium would generate sufficient radiation to contaminate 200,000 square miles (520,000 km2) (an area that is slightly larger than Spain or Thailand, though smaller than France). Given the intensity of the γ radiation, not even those in basement shelters could survive within the fallout zone. However, the short half-life of sodium-24 (15 h):25 would mean that the radiation would not spread far enough to be a true doomsday weapon.
A cobalt bomb was first suggested by Leo Szilard, who publicly sounded the alarm against the possible development of a salted thermonuclear bombs that might annihilate mankind in a University of Chicago Round Table radio program on February 26, 1950. His comments, as well as those of Hans Bethe, Harrison Brown, and Frederick Seitz (the three other scientists who participated in the program), were attacked by the Atomic Energy Commission's former Chairman David Lilienthal, and the criticisms plus a response from Szilard were published. Time compared Szilard to Chicken Little while the AEC dismissed his ideas, but scientists debated whether it was feasible or not. The Bulletin of the Atomic Scientists commissioned a study by James R. Arnold, who concluded that it was. Clark suggested that a 50,000 megaton cobalt bomb did have the potential to produce sufficient long-lasting radiation to be a doomsday weapon, in theory, but was of the view that, even then, "enough people might find refuge to wait out the radioactivity and emerge to begin again."
In popular culture
This concept is best known from the Soviet "Doomsday Machine" in the 1964 satirical Cold War film Dr. Strangelove. In the 1957 novel On the Beach by Nevil Shute, the death of all humanity is brought about by the detonation of cobalt bombs in the Northern Hemisphere. In the 1964 James Bond film Goldfinger, the villain's plan is to detonate a “particularly dirty” atomic device, salted with cobalt and iodine inside the United States Bullion Depository at Fort Knox, thereby rendering the U.S.’s gold reserves radioactive for almost six decades. The 1970s movie Beneath the Planet of the Apes featured an atomic bomb that was hypothesized to use a cobalt casing. The use of a salted bomb is a component to the plot of Frank Miller's graphic novel series The Dark Knight Returns and 2008 TV programme Ultimate Force Slow Bomb episode. Also, in the ABC show The Whispers season 1 episode 5, a "salted bomb" was referred to as a nuclear bomb laced with arsenic, also known as "A.S. 33". The final level of Metro Exodus takes place in the city of Novosibirsk, which the main characters surmise was devastated by a nuclear device salted with Cobalt, based on the lack of physical damage to the city yet massive levels of radioactive contamination as well as character dialog.
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