August 15, 1865|
|Died||December 11, 1950(aged 85)|
|Notable students||Kotaro Honda, Hideki Yukawa|
Nagaoka was born in Nagasaki, Japan, and educated at Tokyo University. After graduating in 1887 he worked with a visiting British physicist, Cargill Gilston Knott, on magnetism. In 1893 he traveled to Europe, where he continued his education at the universities of Berlin, Munich, and Vienna. He also attended, in 1900, the First International Congress of Physicists in Paris, where he heard Marie Curie lecture on radioactivity, an event that aroused Nagaoka's interest in atomic physics. Nagaoka returned to Japan in 1901 and served as professor of physics at Tokyo University until 1925. After his retirement, he was appointed a head scientist at RIKEN, and also served as the first president of Osaka University (1931–1934).
Saturnian model of the atom
Physicists in 1900 had just begun to consider the structure of the atom. The recent discovery by J. J. Thomson of the negatively charged electron implied that a neutral atom must also contain an opposite positive charge. In 1903 Thomson had suggested that the atom was a sphere of uniform positive electrification, with electrons scattered through it like plums in a pudding, the plum pudding model.
Nagaoka rejected Thomson's model on the ground that opposite charges are impenetrable. He proposed an alternative model in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings.
In 1904, Nagaoka developed an early planetary model of the atom. Nagaoka's model was based around an analogy to the explanation of the stability of the Saturn rings. (The rings are stable because the planet they orbit is very massive.) The model made two predictions:
- a very massive nucleus (in analogy to a very massive planet)
- electrons revolving around the nucleus, bound by electrostatic forces (in analogy to the rings revolving around Saturn, bound by gravitational forces).
Both predictions were successfully confirmed by Rutherford (who mentions Nagaoka's model in his 1911 paper in which the nucleus is proposed). However, other details of the model were incorrect. In particular, charged rings would be unstable due to repulsive disruption, which is not the case with Saturn's rings, and Nagaoka himself abandoned it in 1908.
Ernest Rutherford and Niels Bohr presented the more viable Bohr model in 1913.
Nagaoka later did research in spectroscopy and other fields. In 1909, he published a paper on the inductance of solenoids. In March 1924, he described studies in which he had successfully formed a milligram of gold and some platinum from mercury.
Awards and recognition
- For his lifetime of scientific work, Nagaoka was granted the Order of Culture by the Japanese government in 1937.
- The Nagaoka crater on the Moon is named after him.
-  H. Nagaoka
- C.C. Gillispie, ed. (2000). Concise Dictionary of Scientific Biography (2nd ed.). Charles Scribner's Sons. pp. 606–607. ISBN 0-684-80631-2.
- C.C. Gillispie, ed. (1974). Dictionary of Scientific Biography. IX: A.T. Macrobious – K.F. Naumann. Charles Scribner's Sons. p. 648. ASIN B000QA98QQ.