Upon returning to the Weizmann Institute, he was appointed Vice President and, two years later, elected fifth President of the Institute, a position he held for three years. In 1975, he was named Institute Professor. Turning his attention to the subject of water, he served as Chairman of Israel's Desalination Committee from 1966 to 1981. Global disillusionment in the nuclear power spurred him on to an interest in renewable sources of energy. He placed the need to exploit solar energy for diverse purposes on the Weizmann Institute and national agenda. Returning later to the basic aspects of nuclear reactions, he and his colleagues represented Israel at GALLEX, an experiment conducted by an international team in an underground laboratory in Italy’ Gran Sasso region, with the aim of measuring the flux of neutrinos, fundamental particles that reach the earth from the core of the sun. On the international scene, he served as a member of the Scientific Advisory Committee of the United Nations’ International Atomic Energy Agency in Vienna (1973-1981) and was a member of the Executive Committee of the International Energy Agency's SolarPACES project (1991-1993).