Mock Up Of Nuclear Bomb In A Suitcase – James Burke (1978)

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Are Suitcase Bombs Possible?

By Carey Sublette Last changed 18 May 2002

It is impossible to verify at the time of this writing whether nuclear devices sized to fit in side a suitcase were actually manufactured by the former Soviet Union, as alleged by Alexander Lebed in September 1997. It is certainly possibel to assess the technicial plausibility of such a claim and to provide a analysis of the likely characteristics of the weapons Lebed described.

A suitcase bomb with dimensions of 60 x 40 x 20 centimeters is by any standard a very compact nuclear weapon. Information is lacking on compact Soviet weapons, but a fair amount of information is available on compact US designs which provides a good basis for comparison.

The smallest possible bomb-like object would be a single critical mass of plutonium (or U-233) at maximum density under normal conditions. An unreflected spherical alpha-phase critical mass of Pu-239 weighs 10.5 kg and is 10.1 cm across.

A single critical mass cannot cause an explosion however since it does not cause fission multiplication, somewhat more than a critical mass is required for that. But it does not take much more than a single critical mass to cause significant explosions. As little an excess as 10% (1.1 critical masses) can produce explosions of 10-20 tons. This low yield seems trivial compared to weapons with yields in the kilotons or megatons, but it is actually far more dangerous than conventional explosives of equivalent yield due to the intense radiation emitted. A 20 ton fission explosion, for example, produces a very dangerous 500 rem radiation exposure at 400 meters from burst point, and a 100% lethal 1350 rem exposure at 300 meters. A yield of 10-20 tons is also equal to the yield of the lowest yield nuclear warhead ever deployed by the US — the W-54 used in the Davy Crockett recoilless rifle.

A mere 1.2 critical masses can produce explosive yield of 100 tons, and 1.35 critical masses can reach 250 tons. At this point a nation with sophisticated weapons technology can employ fusion boosting to raise the yield well into the kiloton range without requiring additional fissile material.

The amount of fissile material that constitutes a “critical mass” varies with the material density and the type of neutron reflector present (if any). A high explosive implosion can compress fissile material to greater than normal density, thus reducing the critical mass. A neutron reflector reduces neutron loss and reduces the critical mass at a constant density. However generally speaking, adding explosives or neutron reflectors to a core adds considerably more mass to the whole system than it saves.

A limited exception to this is that a thin beryllium reflector (thickness no more than the core radius) can actually reduce the total mass of the system, although it increases its overall diameter. For beryllium thicknesses of a few centimeters, the radius of a plutonium core is reduced by 40-60% of the reflector thickness. Since the density difference between these materials is on the order of 10:1, substantial mass savings (a couple of kilograms) can be achieved. At some point though increasing the thickness of the reflector begins to add more mass than it saves since volume increases with the cube of the radius. This marks the point of minimum total mass for the reflector/core system.

A low yield minimum mass or minimum volume weapon would thus use an efficient fissile material (plutonium or U-233), a limited amount of high explosives (sufficient only to assembly the core, not to compress it to greater than normal density), and a thin beryllium reflector.

We can now try to estimated the absolute minimum possible mass for a bomb with a significant yield. Since the critical mass for alpha-phase plutonium is 10.5 kg, and an additional 20-30% of mass is needed to make a significant explosion, this implies 13 kg or so. A thin beryllium reflector can reduce this by a couple of kilograms, but the necessary high explosive, packaging, triggering system, etc. will add mass, so the true absolute minimum probably lies in the range of 11-15 kg (and is probably closer to 15 than 11).

This is probably a fair description of the W-54 Davy Crockett warhead. This warhead was the lightest ever deployed by the US, with a minimum mass of about 23 kg (it also came in heavier packages) and had yields ranging from 10 tons up to 1 Kt in various versions. The warhead was basically egg-shaped with the minor axis of 27.3 cm and a major axis of 40 cm. The test devices for this design fired in Hardtack Phase II (shots Hamilton and Humboldt on 15 October and 29 October 1958) weighed only 16 kg, impressively close to the minimum mass estimated above. These devices were 28 cm by 30 cm…

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  • Reply
    The Professor
    May 22, 2017 at 12:23 am

    Nice write-up by Carey Sublette. However, I've seen other figures in other sources. For example, André Gsponer, a Swiss expert in this field, writes in his 2009 book, "The Physical Principles of Thermonuclear Explosives" (see page 29 et passim, link below) that a typical boosted pit would contain about 4 kilograms of fissile material (plutonium-239), surrounded by a beryllium reflector of 2-3 kg. In other places, I've seen unverified statements to the effect that pits might contain as little as 2-3 kg of plutonium. For uranium, the numbers are higher, by a factor three or so. In other words, the 4 kg of Pu-239 would correspond to about 12 kg of U-235 (or U-233).

    Sublette's figure of 10.5 kg for the Pu-239 critical mass is correct as such, but irrelevant to nuclear weapons, as it refers to the critical mass for uncompressed plutonium. The explosives in a nuclear bomb serve to compress the pit, which increases the density of the fissile material and reduces the critical mass (as the atoms come closer to one another, which increases the probability of unleashed neutrons "hitting and splitting" the another nuclueus). What is more, with an external neutron source and a boosted pit, the critical mass can be reduced still further. Having looked into the matter in some detail, I'd probably keep to Gsponer's 4 kg plutonium (~12 kg uranium).

    In addition to this, we also know that nuclear explosives can be fitted into 155 mm artillery shells, and I've even heard that it's been done with 125 mm shells. Whether the latter is true or not doesn't matter much, as the former is all we need to know in order to conclude that "suitcase nukes" are indeed technically feasible. In practice, however, they would probably put it in a backpack rather than a suitcase. We also know that the yield of a nuclear bomb could be made as low as 10 tons (0.010 kilotons) of TNT, which is way down in the controlled-fizzle region. Note that a boosted pit would yield a lot more than that, the point being that truly low-yielding nukes cannot be boosted but must rely on pure fission in a controlled fizzle. The burn rate for "Little Boy" (the Hiroshima bomb) was only about 1.6% or so, which consumed about 1 kg of the 64 kg of uranium-235 contained in that bomb. In rough numbers, therefore, 1 kg of burned U-235 corresponds to 20 kilotons in yield. A modern boosted pit will have a burn rate north of 10%, which implies yields north of 20 kilotons for boosted 12 kg uranium pits.

    Finally, there is every reason to believe that portable nuclear devices of this kind were employed to bring down the Twin Towers of the World Trade Center on 9/11. The required yields would be around 300 to 400 tons, but they would have opted for "clean" designs, known as MRR (minimum residual radiation). We know that these designs exist and that they're capable of reducing the residual radiation by at least 99% compared to regular battlefield nukes. We also know that exploding a nuke in an (unstemmed) underground vertical shaft ensures that about 90% of the fission products ("fallout") remains in the hole and only about 10% escapes. If you to the maths, 10% of a 99%-reduced MRR means that the actual fallout would be at least 99.9% below an ordinary battlefield nuke, and most of that would be trapped in the building materials anyway. In other words, nuking the WTC would not have produced a radioactive disaster as many seem to believe.

    We can prove that nuclear fission did take place at the WTC on 9/11, as it is the only possible cause of the epidemic in thyroid cancer observed amongst first responders. The standardised incidence ratio (SIR) for thyroid cancer sits north of 10 (!) for the subperiod 2009-2013, which means that thyroid cancer was ten times higher than expected. Unlike other cancers, thyroid cancer has only one "environmental" (i.e. non-genetic) cause, and that is iodine-131, a fission product with a half life of about eight days, and which accumulates in the thyroid of those exposed, irradiates it, and causes cancer. In addition to the thyroid-cancer smoking gun, we also have correlation patterns in dust samples collected by USGS in the week following 9/11. I've done a statistical study of the published dust data, and found that uranium, thorium, lithium and beryllium form a tight correlation cluster, meaning they're all highly correlated to one another. That uranium and thorium should be highly correlated is probably not all that surprising, nor is it surprising that lithium and beryllium should be correlated. The surprise is that uranium-thorium is so highly correlated to lithium-beryllium. High correlations indicate that they came from the same source. A MRR nuclear device would have an uranium pit, a beryllium reflector, and lithium deuteride as fuel in the fusion "secondary" (cf. Teller-Ulam design). As if that weren't enough, cadmium is also fairly tightly correlated with the other four elements, and cadmium would be the material of choice (together with boron, which unfortunately isn't included in the USGS data) for the MRR casing, as it absorbs neutrons and thus prevents residual radiation through "neutron activation".

    Long note, sorry about that. Thanks for posting this video. Keep up the good work!

  • Reply
    Shaiah Eyes2c
    May 22, 2017 at 12:23 am

    Jews nuked WTC, NY city, on 911

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