In the same interview that I cited the other day, Herbert York also mentioned this fact about thermonuclear weapons:

The simple fact is every hydrogen bomb there is was invented by, was based on technology fully known by 1960. There hasn’t been anything in 50 years that matters. Some of the ideas from 1960 didn’t get made until 1970, but there’s nothing new. It’s a totally mature thing. The only things that are like new are like modem refrigerators are better than they were 20 years ago, they’re still the same thing. They’ve got better hinges, more space on the door…