Salted bomb

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A salted bomb is a nuclear weapon constructed like fission-fusion-fission weapons, but instead of a fissionable jacket around the secondary stage fusion fuel, a blanket of a specially chosen isotope of a non-fissionable element is used, (cobalt-59 in the case of the cobalt bomb). This blanket captures the escaping neutrons from the secondary to breed a radioactive isotope that maximizes the radiation hazard from the weapon rather than generating additional explosive force from fast fission of U-238. The primary purpose of this weapon is to create extreme radioactive fallout to deny a region to an advancing army, a sort of wind-deployed mine-field.

Contents

1 Salting agents
2 Doomsday device
3 Implementation
4 References
5 See also

Salting agents

Variable fallout effects can be obtained by using different salting isotopes. Gold has been proposed for short-term fallout (days), tantalum and zinc for fallout of intermediate duration (months), and cobalt for long term contamination (years). Arsenic and Sodium could also be used for very short-term fallouts. To be useful for salting, the blanket element must be abundant in the natural isotope, so that expensive purification is not needed. Also, the neutron-bred radioactive product must be a strong emitter of high energy penetrating gamma rays, either directly or through indirect decay pathways.

::::::::Candidate Salting Agents

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Parent Isotope	Natural Abundance	Radioactive Product	Half-Life	Average Radiation Energy
Sodium-23	100%	Na-24	14.959 hours	2.7 MeV
Arsenic-75	100%	As-76	1.0778 days	1.13 MeV
Gold-197	100%	Au-198	2.697 days	.411 MeV
Tantalum-181	99.99%	Ta-182	115 days	1.12 MeV
Zinc-64	48.89%	Zn-65	244 days	1.11 MeV
Cobalt-59	100%	Co-60	5.26 years	1.33 MeV

Doomsday device

The idea of the cobalt bomb originated with Leo Szilard who publicized it in Feb. 1950, not as a serious proposal for weapon, but to point out that it would soon be possible in principle to build a doomsday device that could kill everybody on earth. To design such a theoretical weapon a radioactive isotope is needed that can be dispersed world wide before it decays. Such dispersal takes many months to a few years so the half-life of Co-60 is ideal.

Initially gamma radiation fission products from an equivalent size fission-fusion-fission bomb are much more intense than Co-60: 15,000 times more intense at 1 hour; 35 times more intense at 1 week; 5 times more intense at 1 month; and about equal at 6 months. Thereafter fission drops off rapidly so that Co-60 fallout is 8 times more intense than fission at 1 year and 150 times more intense at 5 years.

What is unusual about this type of bomb is the combination of relatively long half-life (5.27 years) with an intensity of radiation still lethal to human beings. The fallout of other nuclear weapons has the appearance of sand or ground pumice, which falls back to the ground in short time, and can be filtered by even a handkerchief, unlike Cobalt-60. After fifteen to twenty years, the Cobalt-60 would have decayed to harmless Nickel-60 and the radiation would decrease by a factor of eight to sixteen, presumably allowing people to return.

Zinc has been proposed as an alternate candidate for the "doomsday role". The advantage of Zn-64 is that its faster decay leads to greater initial intensity. Disadvantages are that since it makes up only half of natural zinc, it must either be isotopically enriched or the yield will be cut in half; that it is a weaker gamma emitter than Co-60, putting out only one-fourth the gamma intensity for the same mass; thus it will decay during the world-wide dispersal process. Assuming pure Zn-64 is used, the radiation intensity of Zn-65 would initially be twice as much as Co-60. This would decline to being equal in 8 months, in 5 years Co-60 would be 110 times as intense.

Prolonged contamination is undesirable in a militarily useful radiological weapon, which would use local (as opposed to world-wide) contamination, and would require high initial intensities for a rapid effect. For this reason Zn-64 is possibly better suited to military applications than cobalt, but probably inferior to tantalum or gold.

Compared to other nuclear weapons, a salted bomb of low explosive yield could kill off life in an area while leaving buildings and machinery intact, in this way a salted bomb is comparable to a neutron bomb. The advantage a salted bomb has over a neutron bomb is that it can be used over a much wider area and can render an area inaccessible for a controlled amount of time, disadvantages are that it is not likely to incapacitate immediately and it may rely on unpredictable winds to deliver the fallout to a target.

Implementation

No salted weapons have ever been atmospherically tested, and as far as is publicly known none have ever been built. However, early nuclear weapons such as "Little Boy" and "Fat Man" tended to disperse large amounts of radioactive contamination in the form of nuclear fallout. During the 1950s, there was considerable debate over whether "clean" bombs could be produced, and these were often contrasted with "dirty" bombs. However, a number of very "dirty" thermonuclear devices have been developed and detonated, of which the final fission stage (usually a jacket of natural or enriched uranium) is essentially analogous to salting (for example, the Castle Bravo shot) although a uranium jacket’s primary use is to produce more explosive energy, more fallout is only a side-effect. The term dirty bomb is now mostly used for a Radiological Dispersal Device (RDD), a radiological weapon which combines radioactive material with conventional explosives.

The British did test a bomb that incorporated cobalt as an experimental radio-chemical tracer (Antler/Round 1, 14 September 1957). This 1 kt device was exploded at the Tadje site, Maralinga range, Australia. The experiment was regarded as a failure and not repeated [link].

Salted bomb

Salting agents

Doomsday device

Implementation

References

See also