Masatoshi Koshiba
1926–2020, Toyohashi, Japan, Tokyo, Japan
Japanese physicist who led Kamiokande — the detector that recorded neutrinos from supernova SN 1987A, establishing neutrino astronomy.
Koshiba graduated from the University of Tokyo in 1951, earned his PhD at Rochester in 1955, then returned to Tokyo as professor. He built Kamiokande inside the Kamioka zinc mine — originally to search for proton decay, but the 3,000-tonne water Cherenkov detector proved ideal for neutrinos.
On 23 February 1987, Kamiokande recorded 11 neutrinos from supernova SN 1987A — the first detection of neutrinos from beyond the Solar System, confirming core-collapse theory. The detector also confirmed Davis's solar neutrino deficit, and its successor Super-Kamiokande later proved neutrino oscillations. He received the 2002 Nobel Prize.
Nobel-winning work
Kamiokande — 'Kamioka Nucleon Decay Experiment' — was a 3,000-tonne tank of ultra-pure water beneath 1,000 m of rock, lined with photomultipliers recording Cherenkov flashes when neutrinos struck the water. The detector measured the solar-neutrino flux and confirmed Davis's 'deficit' with a completely different method.
The climax came on 23 February 1987: a dozen neutrino events (11 at Kamiokande) from supernova SN 1987A in the Large Magellanic Cloud arrived before the light, exactly as gravitational-collapse theory predicts — most of a supernova's energy escapes as neutrinos. It was the founding event of observational neutrino astronomy; Kamiokande data also laid ground for Super-Kamiokande's discovery of neutrino oscillations (1998, Nobel 2015 for Kajita).
Workplaces: University of Tokyo
Japan