It was before the first hydrogen bomb was tested.
An American theoretical physicist was trekking with a Russian theoretical physicist.
The American physicist mentioned to his Russian friend that X-rays could be used as a container not only to hold the hydrogen gas but also can be used to create enormous pressure to start fusion reaction.
The American physicist was surprised when he found that his Russian friend was not at all surprised by what he had told but started asking questions to find how much more the American knew about that property of X-ray.
X-ray being of very short wavelength behave more like a particle that of a wave.
The fact is Russians, even though stole the secret of atomic bomb with the help of physicist named Klaus Fuchs but developed the secret of Hydrogen bomb by themselves.