Frédéric Joliot-Curie, Hans von Halban, Lew Kowarski and Francis Perrin had shown that when fission occurs in a uranium nucleus, two or three extra neutrons are also given off.
Frédéric Joliot-Curie, Hans von Halban, Lew Kowarski, and Francis Perrin. In February 1939, the Paris Group showed that when fission occurs in a uranium nucleus, two or three extra neutrons are also given off.