Via Panisperna boys' patent "To increase the production of artificial radioactivity with neutron bombardment". He was made a temporary assistant at the Royal Institute of Physics on 1 November 1934 and the University of Rome, and on 7 November, he was listed as co-author, along with Fermi and Rasetti, of a landmark paper on slow neutrons that reported that hydrogen slowed neutrons more than heavy elements, and that slow neutrons were more easily absorbed. An Italian patent was granted for the process in October 1935, in the name of Fermi, Pontecorvo, Edoardo Amaldi, Franco Rasetti and Emilio Segrè. A US patent was granted on 2 July 1940. Early career In February 1936, Pontecorvo left Italy and moved to Paris to work in the laboratory of Irène and Frédéric Joliot-Curie at the Collège de France on a one-year scholarship to study the effects of collisions of neutrons with protons and on the electromagnetic transitions among isomers. During this period, influenced by his cousin, Emilio Sereni, he adopted the ideals of communism to which he remained loyal for the rest of his life. He formed a relationship with Helene Marianne Nordblom, a Swedish woman working in Paris as a nanny. Whether because of his relationship with Marianne, his interesting work on isomers, or the deteriorating political situation in Italy, he turned down an opportunity in 1937 to apply for a tenured position at the University of Rome to stay in Paris. Marianne moved in with Pontecorvo at the Hôtel des Grands Hommes on the Place du Panthéon on 4 January 1938. Their son, Gil, was born on 30 July. Her visa expired, and she had to return to Sweden in September. Pontecorvo accompanied her, leaving Gil behind in a residential nursery in Paris. Travelling back to Paris alone, he dined with Manne Siegbahn and met with Niels Bohr and Lise Meitner on 12 October 1938. Pontecorvo was now unable to return to Italy because of the Fascist regime's racial laws against the Jews. This caused the breakup of the Via Panisperna boys, with Fermi moving to the United States. Pontecorvo's family also dispersed. Guido moved to Britain in 1938, followed by Giovanni, Laura and Anna in 1939, while Gillo joined Pontecorvo in Paris. Working in collaboration with the French physicist André Lazard at Joliot-Curie's laboratory at Ivry-sur-Seine, Pontecorvo discovered what Frédéric Joliot-Curie called "nuclear phosphorescence"; the emission of X-rays when neutrons and