Editing Nuclear weapon design (section)

===Fallout analysis===
{{See also|Nuclear forensics}}
The most interesting data from Castle Bravo came from radio-chemical analysis of weapon debris in fallout. Because of a shortage of enriched lithium-6, 60% of the lithium in the Shrimp secondary was ordinary lithium-7, which doesn't breed tritium as easily as lithium-6 does. But it does breed lithium-6 as the product of an (n, 2n) reaction (one neutron in, two neutrons out), a known fact, but with unknown probability. The probability turned out to be high.{{Citation needed|date=June 2021}}

Fallout analysis revealed to designers that, with the (n, 2n) reaction, the Shrimp secondary effectively had two and half times as much lithium-6 as expected. The tritium, the fusion yield, the neutrons, and the fission yield were all increased accordingly.<ref>{{cite book |first=Richard |last=Rhodes |title=Dark Sun; the Making of the Hydrogen Bomb |url-access=limited |publisher=Simon and Schuster |year=1995 |page=[https://archive.org/details/darksunmakinghyd00rhod/page/n568 541] |isbn=9780684804002 |url=https://archive.org/details/darksunmakinghyd00rhod}}</ref>

As noted above, Bravo's fallout analysis also told the outside world, for the first time, that thermonuclear bombs are more fission devices than fusion devices. A Japanese fishing boat, ''[[Daigo Fukuryū Maru]]'', steamed home with enough fallout on her decks to allow scientists in Japan and elsewhere to determine, and announce, that most of the fallout had come from the fission of U-238 by fusion-produced 14 MeV neutrons.{{Citation needed|date=June 2021}}