This resultant extra fuel ( both lithium-6 and lithium-7 ) contributed greatly to the fusion reactions and neutron production and in this manner greatly increased the device 's explosive output . The test used lithium with a high percentage of lithium-7 only because lithium-6 was then scarce and expensive ; the later '' Castle Union '' test used almost pure lithium-6 . Had sufficient lithium-6 been available , the usability of the common lithium-7 might not have been discovered
Castle Union
Castle Union
Castle Bravo