I suspect salting with something like cobalt would dramatically reduce the direct effects of weapons.
Not based on my understanding of H-bombs. For one thing, you need a tamper made of something dense, and depleted uranium U-238 is used if you want to roughly double your yield while massively increasing the fallout created, then it becomes a fission -> fusion -> fission bomb. Lead is substituted for weapons like the one off 50 Gt Tsar Bomba, even the Soviet weren't willing to damage that much of their territory, and there were minor details like pilot survival (https://en.wikipedia.org/wiki/Tsar_Bomba). That tamper could perhaps be made out of cobalt, or you could wrap the "physics package" in cobalt.
But it would be a fairly daft thing to do, cobalt-60 has, compared to normal fission products, a long half-life of 5 years, so that which would eventually fall out of the stratosphere would make things uncomfortable for you (normally it will decay to a de minimis level by the time it comes back down in quantity).
On the other hand, it was pure propaganda to suggest such weapons would kill all life on earth. Ignoring details like the impossibility of getting even enough distribution, and that the earth is big, really only issue for humans who want to survive it, who'd be in heavy fallout areas, and who had any time to prepare is having enough food until it decayed enough, more of a lifeboat ethics sort of thing instead of the all but explicit message that we should surrender to the USSR because we and they were so crazy we might do something like that (and evil; if we, the far more evil nuclear power after JFK and McNamara changed our policy to MAD, weren't going to do it, there was no danger).
Not based on my understanding of H-bombs. For one thing, you need a tamper made of something dense, and depleted uranium U-238 is used if you want to roughly double your yield while massively increasing the fallout created, then it becomes a fission -> fusion -> fission bomb. Lead is substituted for weapons like the one off 50 Gt Tsar Bomba, even the Soviet weren't willing to damage that much of their territory, and there were minor details like pilot survival (https://en.wikipedia.org/wiki/Tsar_Bomba). That tamper could perhaps be made out of cobalt, or you could wrap the "physics package" in cobalt.
But it would be a fairly daft thing to do, cobalt-60 has, compared to normal fission products, a long half-life of 5 years, so that which would eventually fall out of the stratosphere would make things uncomfortable for you (normally it will decay to a de minimis level by the time it comes back down in quantity).
On the other hand, it was pure propaganda to suggest such weapons would kill all life on earth. Ignoring details like the impossibility of getting even enough distribution, and that the earth is big, really only issue for humans who want to survive it, who'd be in heavy fallout areas, and who had any time to prepare is having enough food until it decayed enough, more of a lifeboat ethics sort of thing instead of the all but explicit message that we should surrender to the USSR because we and they were so crazy we might do something like that (and evil; if we, the far more evil nuclear power after JFK and McNamara changed our policy to MAD, weren't going to do it, there was no danger).