4 ms·

Fission bombs can be tested with subcritical explosions. You have a plutonium core (a sphere the size of a grapefruit) and surround it with high explosives. Not

Fission bombs can be tested with subcritical explosions. You have a plutonium core (a sphere the size of a grapefruit) and surround it with high explosives. Not as many as for an actual detonation. You blow them up, create the implosion, and trigger a subcritical fission reaction, or one that is very slightly supercritical. You then take lots of measurements (temperature increase, X and gamma rays, neutrons, etc) and see if they align with your theoretical models. If they do, you have extremely high confidence that the bomb will work as designed. Now, virtually all nukes in the US arsenal have a fusion bomb stage too. The way that works in practice is this: you first detonate the fission component of the bomb, and that produces a huge amount of X-rays. It's so huge that the wavefront of the X-rays behaves like a solid hammer. That's what produces the compression for the secondary. This design is called the Teller-Ulam design, and it is extremely likely that it was discovered only once (by Ulam and Teller), all other thermonuclear bombs are just the result of successful spying and secret sharing. This X-ray hammer can't be very easily tested. That's what these guys are doing. Now, you may wonder if Putin's guys are doing an equally good job at testing their thermonuclear bombs. We don't know, but it doesn't make a difference: the fission part of the bombs is powerful enough to create utter devastation. The fusion part adds some extra punch, but it doesn't change the scale of devastation. And the CIA is highly confident that Russia is properly testing the fission bombs, even undergoing what is called "hydronuclear" tests, which, although not formally banned, other countries don't do.

deepnotderp 3y ago
> This design is called the Teller-Ulam design, and it is extremely likely that it was discovered only once (by Ulam and Teller), all other thermonuclear bombs are just the result of successful spying and secret sharing. Hans Bethe believed that the Soviets and the British got it by analyzing the fallout from fusion bomb tests. Apparently the high number of heavy elements suggested high rates of compression
- credit_guy 3y ago
  Hans Bethe guessed based on the information available to him at the time. But there was information not available to the West prior to the end of the Cold War. In December 1991 two US atomic scientists, Danny Stillman and Nerses Krikorian visited the head of the former Soviet nuclear program, Yuliy Khariton [1]. In their discussions, the Americans realized that even Khariton was not aware of the extent of the Soviet spying. In any case, Khariton had a very dubious recollection of who came up with the idea of the radiation implosion (the Teller-Ulam design). This was such an ingenious idea that if it had indeed originated with one of the Soviet scientists, it would have been memorable. By the way, the Soviets did come up with a thermonuclear design, dubbed "layer cake" in the US. But it was an inferior design that resulted in a yield of only 400 kT (the RDS-6 test [2], in August 1953), which was achievable with fission only. In March 54 the US detonated a few hydrogen bombs, and indeed, the Soviets collected radioactive debris. However, Khariton told Stillman that that information was not helpful, aside from the confirmation that higher yields are somehow possible. Throughout the month of March 1954 the Soviets played with a few ideas, but none was good. Then, miraculously in mid-April 1954, Khariton claims that his deputy Yakov Zeldovich [3] came up with the idea of radiation implosion. But other Soviet nuclear scientists that Stillman and Krikorian interviewed stated that they never heard Zeldovich confirm that story. Moreover, one of these scientists , Lev Feoktistov stated quite candidly "We had neither drawings nor accurate data from the outside, but we were prepared to catch hints and half-hints. I can't shake the feeling that in those times, we were not completely independent" Stillman put all these things (and quite some more) in a book, The Nuclear Express [4]. [1] https://en.wikipedia.org/wiki/Yulii_Khariton https://en.wikipedia.org/wiki/Yulii_Khariton [2] https://en.wikipedia.org/wiki/Joe_4 https://en.wikipedia.org/wiki/Joe_4 [3] https://en.wikipedia.org/wiki/Yakov_Zeldovich https://en.wikipedia.org/wiki/Yakov_Zeldovich [4] https://www.google.com/books/edition/The_Nuclear_Express/qLTuAAAAMAAJ?hl=en https://www.google.com/books/edition/The_Nuclear_Express/qLT...

deepnotderp 3y ago

> This design is called the Teller-Ulam design, and it is extremely likely that it was discovered only once (by Ulam and Teller), all other thermonuclear bombs are just the result of successful spying and secret sharing. Hans Bethe believed that the Soviets and the British got it by analyzing the fallout from fusion bomb tests. Apparently the high number of heavy elements suggested high rates of compression

credit_guy 3y ago
Hans Bethe guessed based on the information available to him at the time. But there was information not available to the West prior to the end of the Cold War. In December 1991 two US atomic scientists, Danny Stillman and Nerses Krikorian visited the head of the former Soviet nuclear program, Yuliy Khariton [1]. In their discussions, the Americans realized that even Khariton was not aware of the extent of the Soviet spying. In any case, Khariton had a very dubious recollection of who came up with the idea of the radiation implosion (the Teller-Ulam design). This was such an ingenious idea that if it had indeed originated with one of the Soviet scientists, it would have been memorable. By the way, the Soviets did come up with a thermonuclear design, dubbed "layer cake" in the US. But it was an inferior design that resulted in a yield of only 400 kT (the RDS-6 test [2], in August 1953), which was achievable with fission only. In March 54 the US detonated a few hydrogen bombs, and indeed, the Soviets collected radioactive debris. However, Khariton told Stillman that that information was not helpful, aside from the confirmation that higher yields are somehow possible. Throughout the month of March 1954 the Soviets played with a few ideas, but none was good. Then, miraculously in mid-April 1954, Khariton claims that his deputy Yakov Zeldovich [3] came up with the idea of radiation implosion. But other Soviet nuclear scientists that Stillman and Krikorian interviewed stated that they never heard Zeldovich confirm that story. Moreover, one of these scientists , Lev Feoktistov stated quite candidly "We had neither drawings nor accurate data from the outside, but we were prepared to catch hints and half-hints. I can't shake the feeling that in those times, we were not completely independent" Stillman put all these things (and quite some more) in a book, The Nuclear Express [4]. [1] https://en.wikipedia.org/wiki/Yulii_Khariton https://en.wikipedia.org/wiki/Yulii_Khariton [2] https://en.wikipedia.org/wiki/Joe_4 https://en.wikipedia.org/wiki/Joe_4 [3] https://en.wikipedia.org/wiki/Yakov_Zeldovich https://en.wikipedia.org/wiki/Yakov_Zeldovich [4] https://www.google.com/books/edition/The_Nuclear_Express/qLTuAAAAMAAJ?hl=en https://www.google.com/books/edition/The_Nuclear_Express/qLT...