Masatoshi Koshiba

Koshiba was born in Toyohashi in central Japan on September 19, 1926, to Toshio and Hayako Koshiba. His father was a military officer. His mother died when he was three, leading to his father marrying his wife's elder sister.[1] He grew up in Yokosuka, and completed his high school in Tokyo. It is mentioned that his initial interest was in studying German literature, but, ended up studying physics, spurred by a teacher's denigrating comments.[1]

He graduated from the University of Tokyo in 1951 and received a Ph.D. in physics from the University of Rochester, New York, in 1955.[2][3]

with Jun'ichirō Koizumi and Kōichi Tanaka (at the Prime Minister's Official Residence on October 11, 2002)

with Jun'ichirō Koizumi (at Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo on August 27, 2003)

Koshiba started his career as a Research Associate at the Department of Physics, University of Chicago from July 1955 to February 1958, and was an associate professor at Institute of Nuclear Study, University of Tokyo from March 1958 to October 1963. While on leave from November 1959 to August 1962 he served as the acting director, Laboratory of High Energy Physics and Cosmic Radiation, Department of Physics, University of Chicago.[2][3] At the University of Tokyo he became associate professor in March 1963 and then professor in March 1970 in the Department of Physics, Faculty of Science, and emeritus professor there in 1987. From 1987 to 1997, Koshiba taught at Tokai University.[3]

In 2002, he jointly won the Nobel Prize in Physics for "pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos". (The other shares of that year's Prize were awarded to Raymond Davis Jr. and Riccardo Giacconi of the U.S.A.)[4]

Koshiba's research focused on neutrinos, subatomic particles with a neutral electric charge and close to zero resting mass. It was believed since the 1920s that the Sun shines because of nuclear fusion reactions that transform hydrogen into helium and release energy. Theoretical calculations indicated that countless neutrinos would have been released in this reaction and exposed the earth to a flood of solar neutrinos. Since these particles interact very weakly with matter, with only one in a trillion stopped on its way to Earth, the neutrinos were considered undetectable.[5] These particles had also been predicted by the theoretical work of Wolfgang Pauli and Enrico Fermi who had used these particles to explain the discrepancy in radioactive decay.[1]

Building on the work of Davis, he built an underground neutrino detector in a zinc mine in Japan in the 1980s. This detector, called Kamiokande, was a gigantic water tank with ultra-pure water and photoelectric detectors on all sides to detect flashes of light generated when neutrinos interact with the atomic nucleus of water molecules. Through this experiment, he was able to prove the hypothesis that neutrinos are generated during the nuclear fusion reaction in the sun. However, the experiments went on to detect fewer neutrinos than had been expected. This deficit was called the solar neutrino problem.[6][1]

In 1988, the Kamiokande experimental detector, with half a million gallons of pure water, detected neutrinos from what is believed to be a supernova explosion outside the Milky Way, the Large Magellanic Cloud.[7][1] His research was pioneering in the establishment of neutrino astronomy as a field of study.[1]

In 1996, with the promising results from Kaokande, the team operationalized a larger and more sensitive detector called Super-Kamiokande. With this detector, scientists was able to demonstrate strong evidence to prove that neutrinos changed from one type to another of three types during flight. This demonstration resolved the solar neutrino problem with the reasoning being that the early detectors could detect one type of neutrino rather than all three types.[8]

Koshiba was a member of the Board of Sponsors of the Bulletin of the Atomic Scientists, and also a foreign fellow of Bangladesh Academy of Sciences.[9] He was a founding member of the Edogawa NICHE Prize Steering committee.[10][11]

Koshiba married Kyoto Kato, an art museum curator, when he returned to Japan in the late 1950s. The couple had a son and a daughter.[1]

He died on November 12, 2020, at the Edogawa Hospital in Tokyo at the age of 94.[12][13][14][15][16]

Source(s):[17]

• 1987 – Asahi Prize
• 1987 – Nishina Memorial Prize
• 1997 – Humboldt Prize
• 2000 – Wolf Prize in Physics
• 2002 – Nobel Prize in Physics
• 2002 – Panofsky Prize
• 2003 – Benjamin Franklin Medal in Physics[18]

Source(s):[17]

• 1985 – Order of Merit of the Federal Republic of Germany
• 1997 – Order of Culture
• 2002 – Honorary citizenship of Suginami[19]
• 2002 – Honorary doctor of Meiji University[20]
• 2002 – Elected Fellow of the American Physical Society.[21]
• 2003 – Grand Cordon of the Order of the Rising Sun[22]
• 2003 – In commemoration of the Nobel Prize-winning by Masatoshi Koshiba, Koshiba hall was established at the University of Tokyo's School of science.[23]
• 2003 – Honorary citizenship of Tokyo
• 2003 – Emeritus Professor of the University of Tokyo

• Koshiba, M.; Fukuda, Y; et al. (1998). "Evidence for Oscillation of Atmospheric Neutrinos". Physical Review Letters. 81 (8): 1562–1567. arXiv:hep-ex/9807003. Bibcode:1998PhRvL..81.1562F. doi:10.1103/PhysRevLett.81.1562.
• Koshiba, M.; Fukuda, Y; et al. (1999). "Constraints on Neutrino Oscillation Parameters from the Measurement of Day-Night Solar Neutrino Fluxes at Super-Kamiokande". Physical Review Letters. 82 (9): 1810–1814. arXiv:hep-ex/9812009. Bibcode:1999PhRvL..82.1810F. doi:10.1103/PhysRevLett.82.1810.

• Institute for Cosmic Ray Research
• Kamioka Observatory
• List of Japanese Nobel laureates
• List of Nobel Laureates affiliated with the University of Rochester
• List of Nobel laureates affiliated with the University of Tokyo
• University of Rochester

• Prof. Koshiba has won the Nobel prize.
• Masatoshi Koshiba on Nobelprize.org including the Nobel Lecture December 8, 2002 Birth of Neutrino Astrophysics
• Freeview video 'An Interview with Masatoshi Koshiba' by the Vega Science Trust