Bayan yakin, Leona Marshall ya koma Jami'ar Chicago, inda ta zama abokin tarayya a Cibiyar Nazarin Nukiliya ta Fermi. A 1960, ta shiga Jami'ar Chicago Pile 3, ta sami hanyar yin amfani da kashi 100 cikin dari na jujjuyawar jujjuyawar neutron, kuma ta ƙayyade ma'auni na ma'auni na neutrons ga abubuwa daban-daban. An haifi ɗanta na biyu, John Marshall III, a 1949. Ta zama mataimakin farfesa a 1953. Bayan mutuwar Fermi a 1954, Marshalls ya rabu. John Marshall ya koma Los Alamos Laboratory, yayin da Leona, yanzu mahaifiyar mahaifa, ya zama abokin tarayya a Cibiyar Nazarin Ci gaba a Princeton, New Jersey a 1957. A shekara mai zuwa ta zama abokin tarayya a Brookhaven National Laboratory, a lokacin da bincike a fannin kimiyyar kimiyyar lissafi ya koma daga ƙwayoyin nukiliya da ƙwayoyin nukiliya.
John Marshall na uku