1. [n]  French nuclear physicist who was Marie Curie's assistant and who worked with Marie Curie's daughter who he married (taking the name Joliot-Curie); he and his wife discovered how to synthesize new radioactive elements (1900-1958)
2. [n]  French physicist who (with her husband) synthesized new chemical elements (1897-1956)

JOLIOT-CURIE is a 12 letter word that starts with J.