Lithium hydride
Before the Castle Bravo nuclear weapons test in 1954, it was thought that only the less common isotope lithium-6 would breed tritium when struck with fast neutrons. The Castle Bravo test showed (accidentally) that the more plentiful lithium-7 also does so under extreme conditions, albeit by an endothermic reaction.
Pacific Proving Grounds
Because of the large amount of atmospheric testing, and especially the Castle Bravo accident of 1954, many of the islands which were part of the Pacific Proving Grounds are still contaminated by nuclear fallout. Many of the island inhabitants at the time of testing suffered from increased incidence of various types of cancers and birth defects.