The device offically designated RDS-220, known to its designers as Big Ivan, and nicknamed in the west Tsar Bomba (and referred to as the Big Bomb by Sakharov in his Memoirs was the largest nuclear weapon ever constructed or detonated. This three stage weapon was actually a 100 megaton bomb design, but the uranium fusion stage tamper of the tertiary (and possibly the secondary) stage(s) was replaced by one(s) made of lead. This reduced the yield by 50% by eliminating the fast fissioning of the uranium tamper by the fusion neutrons, and eliminated 97% of the fallout (1.5 megatons of fission, instead of about 51.5 Mt), yet still proved the full yield design. The result was the “cleanest” weapon ever tested with 97% of the energy coming from fusion reactions. The effect of this bomb at full yield on global fallout would have been tremendous. It would have increased the world’s total fission fallout since the invention of the atomic bomb by 25%.
Note that this document repeats the 97% figure as “coming from fusion reactions”.
No, he’s right. I meant fusion. The Tsar Bomba was both the largest bomb ever detonated and one of the cleanest ones as well.
Basically it was a design for a 100 megaton bomb like you say, but the test shot didn’t have the uranium tamper surrounding the secondary. So 97% of the 50 megaton yield of the test was from fusion. IIRC it was a three stage fusion bomb as well.
The cobalt bomb was the bogey man of Doctor Strangelove style fiction, since cobalt has a nasty half-life; a cobalt jacket would render any area (and probably most of downwind) uninhabitable for centuries.
More specifically: Super-short half-lives (like a few seconds or minutes) aren’t generally much of a problem, because you can just wait them out. And super-long half-lives (like hundreds of millions of years) aren’t too much of a problem, because they last that long by not being very active, so they don’t have much effect. The worst half-lives are the ones that are short enough to be “hot”, but long enough to stay “hot” for a worrisomely long time, on the order of a human lifespan. And cobalt-60 happens to fall in that range.
Even if you could create a fusion bomb without a fission primary, the economics and function of the weapon suggest that you would still use it to fission U238. After all, the purpose of a bomb is to go “boom,” and you get much more boom-for-your-buck by fissioning U238, which is basically free (it’s a waste product, and so cheap it’s used to shoot people with).
These are so-called neutron bombs or Enhanced Radiation Weapons - reduced explosive yield, low fallout, and localized high radiation levels affecting personnel and civilians, but not infrastructure.
And yes, they are still tactical nuclear weapons covered by existing treaties.
Aside: The “tactical” term doesn’t mean anything like “low-yield”. It just means that the weapon is intended to be used against armies in the field, rather than against strategic targets like cities or bases.
And a modern tank is big and heavy enough that unless you’re extremely close to the blast, it’ll still survive being nuked. The crew might get a high enough radiation dose that they’d die in a few years, but if an enemy is bearing down on you in a tank, them dying in a few years is small comfort to you. For a tactical weapon, you want something that’ll stop that tank right now. The best way anyone’s found to do that is to hit the tank with extremely high levels of a sort of radiation that armor isn’t very good at shielding against, high enough that it kills the crew instantly (or at least, in a matter of minutes rather than years). That’s the purpose of neutron bombs, AKA enhanced radiation weapons: It’s not, as is so often claimed, to “leave the buildings still standing”.
The crew may have begun to feel the effects in minutes but I seem to recall that they were still capable of functioning for at least hours if not days afterwards, and as in typical radiation poisoning they had a period of almost normal functioning after being extremely ill before their health dropped off a cliff?
So one of the potential draw-backs is after using a neutron bomb on an advancing tank column you now have an enemy with literally nothing to lose because they know they’re going to die soon anyway, and in a most unpleasant way, so may as well go out fighting.
As I said, going from memory, I have not recently used a tactical nuclear weapon on anyone.
