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Hans Bethe - Work on the carbon/nitrogen cycle of massive stars (73/158)

2,215 views · Published 27 June 2017 · 2:47 · Indexed 18 October 2026

Channel: Web of Stories - Life Stories of Remarkable People · 2017 · Science & Technology

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German-born theoretical physicist Hans Bethe (1906-2005) was one of the first scientists to join the Manhattan Project, later strongly advocating nuclear disarmament. In 1967, he was awarded the Nobel Prize in Physics for his theory of stellar nucleosynthesis. [Listener: Sam Schweber; date recorded: 1996]

TRANSCRIPT: And so I went home from that conference and in the next several weeks I looked at other elements in the periodic table going just systematically to helium. Well, that wouldn't work, helium and hydrogen don't give you anything; helium and helium don't give you anything, because neither lithium-5 nor beryllium-8 are stable nuclei. So you had to go on and when you took lithium, beryllium, boron, they could give you a very big energy production together with hydrogen but they would then be totally exhausted immediately... until I came to carbon and carbon was totally different, namely when you start with carbon and add a hydrogen you get nitrogen-13 which disintegrates spontaneously into carbon-13. You can add another proton, make nitrogen-14, and then another proton making oxygen-15 and nitrogen-15, and finally when you have nitrogen-15 and add a proton, you don't get oxygen-16 as you might believe, but instead it disintegrates into carbon-12 and helium-4. And so you get your initial nucleus back, the carbon only acts as a... as a catalyst to bring four protons together to form a helium nucleus; from that you get all the energy release which is involved in that reaction, and you get it without having to invoke weak interactions like the proton-proton reaction. It is therefore generally accepted now that it is the proton-proton reaction for the sun, but it is the carbon cycle - carbon citrogen cycle - for all massive stars beginning a little below Sirius and going up all the way in the Stellar Table to the most luminous stars.

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