Chao Chung-yao

Chao Chung-yao

Chao Chung-yao ( Chinese  趙忠堯  /  赵忠尧 , Pinyin Zhào Zhōngyáo , W.-G. Chao Chung-yao ; born June 27, 1902 with Zhuji ; † May 28, 1998 in Beijing ) was a Chinese physicist who dealt with experimental nuclear physics concerned.

Chung-Yao Chao studied the scattering of gamma rays in lead by pair generation in 1930 without knowing that positrons were involved in the abnormally high scattering cross-section. When the positron was discovered by Carl David Anderson in 1932 , it confirmed the existence of Paul Dirac's antimatter , which could explain Chung-Yao Chao's previous experiments that gamma rays are emitted from electron-positron annihilation. Anderson, who, like Chao, was a graduate student at Caltech, had seen Chao's experiments and discussed the possibility of using a cloud chamber instead of an electroscope and planned to repeat Chao's experiments with them. At Millikan's insistence, however, he used it to investigate cosmic radiation, where he discovered the positron.

His father was a school teacher and practiced Chinese medicine on the side. He studied from 1920 at the University of Nanjing (then Advanced Normal School and soon after Southeastern University) with a bachelor's degree in physics in 1925 as a student of Ye Qisun (Chi-Sun Yeh), who shortly before in 1923 at Harvard with William Duane and Percy Bridgman had a PhD in experimental physics (and was a student of Robert Millikan in Chicago). In 1927 - he had just married - Cao Chung-yao also went to the USA. He received his doctorate from Nobel Prize winner Robert Andrews Millikan at the California Institute of Technology in 1930, with a thesis on the interaction of hard gamma radiation with matter (examination of the Klein-Nishina cross-section ). While he found a match with Klein and Nishima's formula for light elements, there was a 40% increase in absorption for heavy elements such as lead, which was also discovered around the same time by scientists in Great Britain and Germany. Soon after, he also found anomalous scattering of gamma rays from both lead and aluminum that could not be explained with the previous theory. Like Millikan, Chao suspected contributions from electrons in the nucleus and positrons were only identified as the cause by Anderson's experiments a little later.

Millikan had secured a three-year scholarship from the China Foundation for the Promotion of Education and Culture for Chao, who had only had a small scholarship when he left China and lived on borrowed money and savings. After a trip to Europe (with Gerhard Hoffmann in Halle, whose electroscope (Hoffmann electrometer ) he had used for his experiments, and Ernest Rutherford in Cambridge, who encouraged him to conduct further experiments after his return to China), he returned to China prematurely in 1931 after reports of a Japanese invasion reached him. In China, he continued his experiments at Tsinghua University in Beijing, where he set up a nuclear physics laboratory. In addition to Ye, colleagues were in particular Wu Youxun (Yui Hsun Woo), who made significant contributions to the Compton Effect when he was studying with Arthur Holly Compton in Chicago , and Zhou Peiyuan (Pei Yuan Chou), who had also studied at Caltech. Chao and colleagues also got involved in the industrial development of China by founding a pencil factory. After the Japanese invasion in 1937 he taught at Yunnan University in Kunming and soon afterwards at the exiled Tsinghua University in Kunming (Southwestern Associated University, SAU). From 1945 he taught at Chongqing University , where he headed the physics faculty of the National Central University. In 1946 he was sent to represent China to the Americans' atomic bomb tests on Bikini Atoll and also used his stay in the US to purchase scientific instruments for Academia Sinica. Since Van de Graaff generators were too expensive, he learned how to build them himself from John G. Trump at the Massachusetts Institute of Technology and at the Carnegie Institution in Washington DC. His return to China was delayed until 1950 due to the civil war. In the meantime, he did research on cosmic rays in Bruno Rossi's group at MIT and on nuclear physics at the Kellogg Laboratory of Caltech with Thomas Lauritsen and others. On his return trip the Korean War had already started and he was held in Japan by the Americans, which led to international entanglements. In 1951 he became director of the nuclear physics department at the Chinese Academy of Sciences in Beijing. There he built Van de Graaf accelerators and the institute also received two cyclotrons from the Soviet Union in the late 1950s. In 1958 he was also head of the physics faculty at the newly founded University of Science and Technology in Beijing. After he had already been distrusted by the communist authorities (he was only marginally involved in the nuclear weapons program), he was temporarily interned during the Cultural Revolution. In the early 1970s, his situation improved and he became deputy director of the newly established Institute for High Energy Physics of the Chinese Academy of Sciences in 1973 and he was fully rehabilitated after Mao's death in 1976.

He was one of the founders of nuclear physics in China and trained several generations of Chinese nuclear physicists. Among them were Chen Ning Yang (at the SAU, where he was mainly a student of Wu Ta-You ) and many physicists from the Chinese atomic bomb project of the 1960s (such as Wang Ganchang ).

literature

• Cong Cao: Chinese Science and the Nobel Prize Complex . In: Minerva . tape 42 , 2004, p. 151-172 ( PDF ).

Individual evidence

1. ^ CY Chao: The Absorption Coefficient of Hard γ-Rays . In: Proc. Nat. Acad. Sci. tape 16 , no. 6 , 1930, p. 431-433 ( PDF ).
2. ↑ Zuoyue Wang: Article Zhao Zhongyao , Dictionary of Scientific Biography

Note: This article places the family name before the person's first name. This is the usual order in Chinese. Chao is the family name here, Chung-yao is the first name.