original passage: The latter of the two equations was unknown when the U.S. conducted the Castle Bravo fusion bomb test in 1954. Being just the second fusion bomb ever tested (and the first to use lithium), the designers of the Castle Bravo "Shrimp" had understood the usefulness of 6Li in tritium production, but had failed to recognize that 7Li fission would greatly increase the yield of the bomb. While 7Li has a small neutron cross-section for low neutron energies, it has a higher cross section above 5 MeV. The 15 Mt yield was 150% greater than the predicted 6 Mt and caused unexpected exposure to fallout.
original sentence: The 15 Mt yield was 150% greater than the predicted 6 Mt and caused unexpected exposure to fallout.
sentence2: If, hypothetically-speaking, arms control agreements were based not on megatons of yield, but instead on some objective measure of the absolute level of fallout that would come about if a country's stockpile of nukes was to be used, would this new 7Li fission development essentially give America a free pass to increase the size of her arsenal?
sentence1: The latter of the two equations was unknown when the U.S. conducted the Castle Bravo fusion bomb test in 1954. Being just the second fusion bomb ever tested (and the first to use lithium), the designers of the Castle Bravo "Shrimp" had understood the usefulness of 6Li in tritium production, but had failed to recognize that 7Li fission would greatly increase the yield of the bomb. While 7Li has a small neutron cross-section for low neutron energies, it has a higher cross section above 5 MeV. The bomb was expected to explode with a yield of 6 megatons, but actually yielded 15, which caused much higher levels of fallout exposure than anyone was expecting at the time of the test.