https://en.wikipedia.org/wiki/Chien-Shiung_Wu
The newly commissioned B Reactor, the first practical nuclear reactor ever built, which was located at the Hanford Site had run into an unexpected problem, starting up and shutting down at regular intervals. John Archibald Wheeler and partner Enrico Fermi suspected that a fission product, Xe-135, with a half-life of 9.4 hours, was the culprit, and might be a neutron poison or absorber.[54] Segrè then remembered the 1940 PhD thesis that Wu had done for him at Berkeley on the radioactive isotopes of Xe and told Fermi to "ask Ms. Wu".[55] The paper on the subject was still unpublished, but after Fermi contacted Wu, Segrè visited her dorm room together with Nichols and collected the typewritten draft prepared for the Physical Review. The suspicions of Fermi and Wheeler came true, Wu's paper unknowingly verified that Xe-135 was indeed the culprit for the B Reactor; it turned out to have an unexpectedly large neutron absorption cross-section.[52] Wu, wary of her publication giving information to other nations on the arms race of the war, waited for a few months before November 1944, when she and Segrè submitted a complete study on these results, which was published months before the bombs were used the next year.[56][57][58] Wu also used her findings in radioactive uranium separation to build the standard model for producing enriched uranium to fuel the atomic bombs at the Oak Ridge, Tennessee facility as well as build innovative Geiger counters.[59]
