Thank you for your responses guys, it's much appreciated. I read that Uranium was the initial choice for the Soviets for the simple fact that it would have resulted in fast fusion, thus increasing the yield of the bomb to somewhere around 80 MT. Their final choice of using lead instead brought...
I've read that the Tsar Bomb used a lead casing for the second and third stages of the bomb instead of a uranium casing. A uranium casing would have resulted in fast fusion but would have created too much fallout. Typical Hydrogen bombs use uranium casings. A uranium casing would have indeed...