You’re talking about Castle Bravo in 1954, not Ivy Mike. Ivy Mike was purely a first time demonstration device that used liquid deuterium for the secondary. Castle Bravo was an actual prototype weapon test that used lithium deuteride for the secondary. Unfortunately, the cross section measurements didn’t catch that Li7D would also participate in the reaction due to the generation of fast neutrons. Hence the yield was 2.5 times greater than expected.
