The Teller Ulam-based " Ivy Mike " device had a much greater yield of 10.4 Mt, but most of this also came from fission : 77 % of the total came from fast fission of its natural-uranium tamper.
12.
The fast fission of the secondary jacket in fission-fusion-fission bombs is sometimes referred to as a " third stage " in the bomb, but it should not be confused with the obsolete true three-stage thermonuclear design, in which there existed another complete tertiary fusion stage.
13.
This eliminated fast fission by the fusion-stage neutrons, so that approximately 97 % of the total yield resulted from thermonuclear fusion alone ( as such, it was one of the " cleanest " nuclear bombs ever created, generating a very low amount of fallout relative to its yield ).
14.
The design of " Grapple Y " was notably successful because much of its yield came from its thermonuclear reaction instead of from the fast fission of a heavy uranium-238 tamper-hence making it a true H-bomb, and also because its yield had been closely predicted indicating that its designers understood what they were doing.
15.
It is not fissile, but is a fertile material : it can capture a slow neutron and after two beta decays become fissile plutonium-239 . Uranium-238 is fissionable by fast neutrons, but cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable.
16.
For example, an estimated 77 % of the 10.4-megaton yield of the Ivy Mike thermonuclear test in 1952 came from fast fission of the depleted uranium Soviet Union's test of the " Tsar Bomba " in 1961 produced " only " 50 megatons of explosive power, over 90 % of which came from fusion, because the 238 U final stage had been replaced with lead.
17.
"' Uranium-238 "'( "'238 U "'or "'U-238 "') is the most common capture a slow neutron and after two beta decays become fissile plutonium-239.238 U is fissionable by fast neutrons, and cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable.
18.
Another method by which neutron radiation can be used to destroy incoming nuclear warheads is by serving as an intense neutron generator and to thus initiate fission in the incoming warhead's fissionable components by fast fission, potentially causing the incoming warhead to prematurely detonate in a fizzle if within sufficient proximity, but in most likely interception ranges, requiring only that enough fissionable material in the warhead fissions to interfere with the functioning of the incoming warhead when it is later fuzed to explode ( see related physics : Subcritical reactor ).
