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In the movie Godzilla at one point the scientists discover a residue of Strontium-90 in Godzilla's footprint. In the ensuing report to the Diet a scientist announces that this is evidence that Godzilla's undersea home was perturbed by a hydrogen bomb.

This would seem to conflict with the Wikipedia article on Strontium-90 which says that the isotope is a product of nuclear fission, not nuclear fusion. Since a hydrogen bomb is a weapon that depends on nuclear fusion, and no mention of nuclear fusion is made in the Wikipedia article, I am wondering if Strontium-90 is found also in detritus of hydrogen bomb explosions and, if so, by what mechanism that occurs.

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    $\begingroup$ An hydrogen bomb requires a traditional thermonuclear bomb to achieve a critical temperature and density to fuse hydrogen. The byproduct of fusion should tipically be helium, but the byproducts in the fission explosion can contain strontium. $\endgroup$
    – GRB
    Dec 28, 2016 at 18:17
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    $\begingroup$ Quoting Wikipedia: 'In many Teller–Ulam weapons, fission of the pusher dominates the explosion and produces radioactive fission product fallout'. A 'Teller-Ulam weapon' is a hydrogen bomb. $\endgroup$
    – user107153
    Dec 28, 2016 at 22:31
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    $\begingroup$ In fact, in some such weapons the main role of the fusion stage is to provide more neutrons to the fission fuel as the blast moves the material apart. The person who described this to me said that a better name for the device would be a "fission$\to$fusion$\to$fission bomb." $\endgroup$
    – rob ♦
    Dec 30, 2016 at 5:15

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A hydrogen bomb needs to attain extremely high temperatures and pressures in order to achieve thermonuclear fusion of hydrogen isotopes.

A standard design appears to be to surround or at least trigger the fusion bomb with a fission bomb (see here for example) in order to compress and heat the hydrogen isotopes to the required levels to initiate fusion. The neutrons from fission can also be used to produce tritium in situ from the more convenient lithium deuteride fuel.

Strontium-90 is typically one of the isotopes produced in the fission of Plutonium or Uranium and therefore would be found in fallout from a fusion bomb.

As the half-life of Strontium-90 is only 28.8 years, then high levels of Strontium-90 would reveal a recent nuclear event (in geological terms), since it would not be present naturally in other than trace quantities.

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