Salted bomb

A salted bomb is a Radiological weapon designed to produce 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 salted bomb has ever been atmospherically tested, and as far as is publicly known none have ever been built.

A salted bomb should not be confused with a dirty bomb, which is an ordinary chemical 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.

Design
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.

One example of a possible salted bomb would be a cobalt bomb, which would produce the radioactive isotope cobalt-60 (60Co). Other radioactive isotopes that have been suggested for salted bombs include gold-198 (198Au), tantalum-182 (182Ta) and zinc-65 (65Zn). Sodium-24 has also been proposed as a salting agent. 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.

In popular culture
This concept is best known from the Soviet "Doomsday Device" 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. 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.