Salted bomb

A salted bomb is a variation of a nuclear 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.

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 chosen for the fallout material is usually a high intensity gamma ray emitter, with a half-life long enough that it remains lethal for an extended period. It also must 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 salted bomb is a proposed cobalt bomb, which produces the radioactive isotope cobalt-60 (⁶⁰Co). Other non-fissionable isotopes can be produced, including gold-198 (¹⁹⁸Au), tantalum-182 (¹⁸²Ta) and zinc-65 (⁶⁵Zn). Sodium-23 has also been proposed as a salting agent.

No salted bomb has ever been atmospherically tested and as far as is publicly known none have ever been built. The United Kingdom did test 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.