The largest man made explosion was done by the soviests in september of 1961. The Tsar Bomba had an estimated yield of 100 megatons.. but a 60 megaton version of it was actualy tested.
Taken from a site:
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the Tsar was exploded with an ultimate yield of about 57 megatons, although nobody is really quite sure exactly. 57 is what the Guinness has as the largest explosion ever. Because it was a three stage fission/fusion/fusion, it was the cleanest buring weapon tested from the standpoint of fallout per megaton, but since the weapon was stupidly large, it was also the single largest source of radioactive debris from all the atmospheric tests. On it's own it contributed about 11% of the global fallout count.
The only place I've seen it credited at 57 megatons is in Trinity and Beyond: The Atomic Bomb Movie and The Guinness Book of World Records. It's generally accepted to have been 50 megatons even though claims range from 46 to 62 megatons, and even the russians who conducted the test still aren't quite sure.
Tsar was the cleanest nuclear weapon ever exploded per unit of explosive yield because the Soviets left its U238 tamper jacket off of the weapon and replaced it with Tungsten to cut down on bomb debris from tertiary fission. As such, the bomb produced yield from two stages - a primary fission device of the implosion design yielding maybe five kilotons, and the remaining 56.95 megatons entirely from two fusion stages, yielding what was probably around 1.5 and 55.45 MT respectively. Tsar used dry Lithium-Deuteride bricks to store deuterium and produce tritium in the presence of the neutron flux from the primary device. It is referred to as a clean weapon because of the debris/yield ratio, but as I said above, it was the dirtiest explosion ever simply because it was so large that the ratio didn't mean dick.
If the Soviets had put the U238 tamper jacket on it, Tsar would have yielded in excess of 100 MT from tertiary fast-fission of the Uranium tamper (this is how all modern 2.5 staged fission-fusion-fission devices function). Tsar epitomized the Cold War fad of nuclear dick waving. It was so large to be utterly impractical for actual use, and the fuels required to produce it were so voluminous that the Soviets would have run themselves dry trying to make more than a few of them.
The Soviets started talking about it in 1958 when the voluntary moratorium began. They could have built it rather quickly since it was a simple design, and ultimately it only took 13 weeks from approval to completion in October of 1961. This thing hadn't really left the conceptual stages until early July of 1961, and for political reasons Khrushchev wanted it for a planned October test series. Given the speed with which they actually did develop and deploy the weapon, there's no reason to believe that they couldn't have done it as early as 1958 or 1959, which is after the Soviets had already demonstrated controlled multi-staged weapon technology.
I saw an actual visual graph somewhere on the net comparing the mushroom cloud from the 1945 atomic tests to the largest american test and to this one.. was very interesting.
Sorry couldn't help myself.
