TOKYO – Professor Masatoshi Koshiba, one of Japan’s most eminent scientists, died on November 12 at the age of 94.
Koshiba shared the 2002 Nobel Prize in Physics with Raymond Davis Jr, and Riccardo Giacconi “for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos.”
Koshiba’s story is one of notable personal achievement in the context of Japan’s recovery from World War II and its development into a major force in science and precision manufacturing.
Davis and his colleagues were the first to detect neutrinos created by nuclear fusion in the sun through their Brookhaven Solar Neutrino Experiment (also known as the Homestake experiment) in the United States in the 1960s. Davis died in 2006.
Koshiba followed up by designing and constructing a neutrino detector in Japan that confirmed Davis’s results in the 1980s. Similar experiments were conducted in the USSR and Italy.
Giacconi was an expert in x-ray astronomy who served as director of the Space Telescope Science Institute (operational center for the Hubble Space Telescope) and director general of the European Southern Observatory, which operates telescopes in northern Chile. He died in 2018.
In Gifu Prefecture, central Japan, one thousand meters underground in the old Mozumi zinc mine of the Kamioka Mining and Smelting Company, is an observatory dedicated to the study of particle physics. Its research is focused on solar neutrinos, neutrinos emitted by supernova in deep space, and atmospheric neutrinos here on earth.
This particular astronomical observatory is located far below ground in order to eliminate interference from cosmic rays. Neutrinos, which can travel through solid rock, are subatomic particles similar to electrons but with no electrical charge and a very small mass. They are very difficult to detect.
Named Kamiokande after the Kamioka Nucleon Decay Experiments first conducted there in the early 1980s, the observatory is now home to Super-Kamiokande, a neutrino detector consisting of a stainless-steel tank 39.3 meters across and 41.4 meters high filled with 50,000 tons of ultra-pure water. About 13,000 photo-multiplier sensors are mounted on the wall of the tank.
Photo-multipliers (also called photon multipliers) are extremely sensitive vacuum tube devices that amplify incident light by up to 100 million times. They collect the pale blue light emitted by neutrinos traveling as fast as light in the water.
Photo-multipliers were invented at RCA Laboratories in the 1930s. Hamamatsu TV, the precursor of Hamamatsu Photonics, began production of photo-multiplier tubes in 1956 and signed a technical support agreement with RCA in 1960.
Hamamatsu Photonics, headquartered in Shizuoka Prefecture, Japan, now has about 90% of the global market for photo-multiplier tubes. In the fiscal year ended September 2020, this business generated ¥53 billion ($508 million) in sales to makers of medical, industrial, analytical, measurement and other instruments – and to research institutes investigating neutrinos.
Super-Kamiokande is operated by an international collaboration of about 150 people and about 40 institutes from Japan, the United States, Korea, China, Poland, Spain, Canada, the UK, Italy and France.
As noted on the Super-Kamiokande website: “The investigation of the neutrino properties will enable us to understand how matter was created in the early universe. By observation of solar neutrinos, we can know the activities inside of the sun. By detection of neutrinos from supernova burst, we can investigate the details of the explosion mechanism of the star.”
The first Kamiokande neutrino detector, called Kamiokande II, was built under Koshiba’s direction. He was also instrumental in the construction of the larger, improved Super-Kamiokande in the 1990s.
Koshiba was born in 1926. He graduated from the University of Tokyo in 1951 and went on to earn a PhD in physics at the University of Rochester, New York, in 1955. He then spent three years as a research associate in the Department of Physics at the University of Chicago.
Koshiba returned to Japan in 1958 to become associate professor at the University of Tokyo’s Institute of Nuclear Study, but went right back to the University of Chicago in 1959 to spend three years as acting director of the Laboratory of High Energy Physics and Cosmic Radiation in the Department of Physics.
He was made a full professor in the Department of Physics at the University of Tokyo in 1970 and Emeritus Professor in 1987. He then taught at Tokai University for 10 years before retiring at the age of 71.
Koshiba finished his career as emeritus professor at the University of Tokyo and senior counselor of the International Center for Elementary Particle Physics.
Japan is the only non-Western nation among the top ten winners of Nobel Prizes, ranking 8th with a total of 28 recipients (including three who subsequently acquired foreign citizenship). India ranks 17th with 12. China ranks 23rd with eight. Taiwan has two. Hong Kong, South Korea, Myanmar and Vietnam each have one.
Koshiba was the fourth Japanese recipient of the Nobel Prize in Physics, of which there have been 11 so far. There have also been eight Japanese recipients of the Nobel Prize in Chemistry and five recipients of the Nobel Prize in Physiology or Medicine.
In addition to Koshiba, the best known of these include:
- Leo Esaki, who shared the 1973 prize in Physics with Ivar Giaever and Brian David Josephson “for their experimental discoveries regarding tunneling phenomena in semiconductors and superconductors.” Esaki’s work at Tokyo Tsushin Kogyo (now Sony) led to the creation of the tunnel diode.
- Shinya Yamanaka, who shared the 2012 prize in Physiology or Medicine with John B. Gorden “for the discovery that mature cells can be reprogrammed to become pluripotent.” Yamanaka is now Director of Center for iPS Cell [induced Pluripotent Stem Cell] Research and Application at Kyoto University.
- Shuji Nakamura, who shared the 2014 prize in Physics with fellow Japanese Isamu Akasaki and Hiroshi Amano “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources.” Nakamura was the one who actually made the first blue light-emitting diode in his lab at Nichia Corporation in Tokushima on the island of Shikoku. His story is told by Bob Johnstone in his book Brilliant: Shuji Nakamura and the Revolution in Lighting Technology.
- Akira Yoshino, who shared the 2019 prize in Chemistry with John B. Goodenough and M. Stanley Whitingham “for the development of lithium-ion batteries.”
- And Takaaki Kajita, a professor at the University of Tokyo who shared the 2015 prize in Physics with Arthur B. McDonald “for the discovery of neutrino oscillations, which shows that neutrinos have mass.” Kajita, a former student of Koshiba’s, also did his prize-winning work at Kamiokande.
According to reports in the Japanese press, Kajita had this to say about Koshiba: “He was my mentor since I entered graduate school. He had a very straight and stubborn attitude, cherishing the ground on which he could devote himself to basic research, and kept telling his students to pursue their dreams. Thanks to Professor Koshiba, I am what I am today.”
Scott Foster is an analyst with Lightstream Research, Tokyo.