His main scientific results were on slow neutrons in the Fermi group, and the evidence for antiproton annihilations with emulsion techniques, somewhat contemporary to its production in accelerators by Emilio Segrè and collaborators. Amaldi co-authored about 200 scientific publications ranging from atomic spectroscopy and nuclear physics to elementary particle physics and experimental gravitation, as well as textbooks for secondary schools and universities. He also wrote historical-scientific books; for example, a biography of his friend Ettore Majorana who mysteriously disappeared. He was elected a Foreign Honorary Member of the Soviet Academy of Sciences in 1958, an International Member of the American Philosophical Society in 1961, and both the American Academy of Arts and Sciences and the United States National Academy of Sciences in 1962. In 1963 he became foreign member of the Royal Netherlands Academy of Arts and Sciences. On 25 April 1968, he was elected as a Foreign Member of the Royal Society.