paper, Pontecorvo listed 21 possible reactions involving neutrinos and noted that some of them could not occur unless the electron neutrino () and the muon neutrino () were one and the same. (Thus an inability to find those reactions would be evidence that there were two types of neutrinos.) This paper introduced this notation for neutrinos, which we use today, and listed the reasons why he felt that having two types of neutrinos was "attractive from the point of view of symmetry and the classification of particles". The prediction that neutrinos associated with electrons are different from those associated with muons was confirmed in 1962. In 1988 Jack Steinberger, Leon M. Lederman and Melvin Schwartz were awarded the Nobel Prize in Physics for the discovery of the muon neutrino. Pontecorvo's solution to the solar neutrino problem involved an idea that he had first considered in 1957, and developed over the following decade. This was the idea that neutrinos may convert into other types of neutrinos, a phenomenon known as neutrino oscillation. Somewhere between the Sun and the Earth, electron neutrinos might transform into muon neutrinos. An important point was that for this to happen, neutrinos could not have zero mass, and therefore could not travel at the speed of light. The existence of the oscillations was finally established by the Super-Kamiokande experiment in 1998 and later confirmed by other experiments. This prediction was recognised by the 2015 Nobel Prize in physics, awarded to Takaaki Kajita and Arthur B. McDonald "for the discovery of neutrino oscillations, which shows that neutrinos have mass". Pontecorvo also predicted in 1958 that supernovae would produce intense bursts of neutrinos. Few scientists were more excited when Supernova SN1987A was detected by neutrino detectors. Pontecorvo died in Dubna on 24 September 1993, afflicted by Parkinson's disease. In accordance with his wishes, half of his ashes were buried in the Protestant Cemetery in Rome, and another half in Dubna in Russia. In 1995, in recognition of his scientific merits, the prestigious Pontecorvo Prize has been instituted by the Joint Institute for Nuclear Research. The prize, awarded annually to an individual scientist, recognises "the most significant investigations in elementary particle physics", as acknowledged by the international scientific community. In 2006, Moscow historical society Moskultprog unveiled an artistic plaque celebrating Pontecorvo's Moscow house at 9 Tverskaya Street. Notes References Further reading External links Biography / Scientific Works / Popular Articles