Hans Bethe

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Hans Bethe : biography

July 2, 1906 – March 6, 2005
link=yes|Proton}}  +  link=yes|Proton}} →  Link|deuterium|2}}  +  link=yes|Positron}}  +  link=yes|Electron Neutrino}}

But this did not account for the observation of elements heavier than helium. By the end of the conference, Bethe, working in collaboration with Charles Critchfield, had come up with a series of subsequent nuclear reactions that explained the how the Sun shines:

Link|deuterium|2}}  +  Proton|link=yes}}  →  Link|helium|3}}  +  link=yes|Gamma}}
Link|helium|3}}  +  Link|helium|3}}  →  Link|helium|4}}  +  Proton|link=yes}}
Link|helium|3}}  +  Link|helium|4}}  →  Link|beryllium|7}}  +  link=yes|Gamma}}
Link|beryllium|7}}  +  link=yes|Electron}}  →  Link|lithium|7}}  +  link=yes|Electron Neutrino}}
Link|lithium|7}}  +  Proton|link=yes}}  →  Link|helium|4}}

That this did not explain the processes in heavier starts was not overlooked. At the time there were doubts about whether the proton–proton cycle described the processes in the Sun, but more recent measurements of the Sun’s core temperature and luminosity show that it does. When he returned to Cornell, Bethe studied the relevant nuclear reactions and reaction cross sections, leading to his discovery of the carbon-oxygen-nitrogen cycle:

link|carbon|12}}  +  Proton|link=yes}}  →  link|nitrogen|13}}  +  link=yes|Gamma}}
link|nitrogen|13}}      →  link|carbon|13}}  +  link=yes|Positron|link=yes}}  +  link=yes|Electron Neutrino}}
link|carbon|13}}  +  Proton|link=yes}}  →  link|nitrogen|14}}  +  Gamma|link=yes}}
link|nitrogen|14}}  +  Proton|link=yes}}  →  link|oxygen|15}}  +  Gamma|link=yes}}
link|oxygen|15}}      →  link|nitrogen|15}}  +  Positron|link=yes}}  +  Electron Neutrino|link=yes}}
link|nitrogen|15}}  +  Proton|link=yes}}  →  link|carbon|12}}  +  link|helium|4}}

The two papers, one on the proton–proton cycle, co-authored with Critchfield, and the other on the carbon-oxygen-nitrogen (CNO) cycle, were sent to the Physical Review for publication. After Kristallnacht , Bethe’s mother had become afraid to remain in Germany. Taking advantage of her Strasbourg origin, she was able to emigrate to the United States in June 1939 on the French quota, rather than the German one, which was full. But the Germans wanted $250 to release her furniture. Bethe’s graduate student Robert Marshak noted that the New York Academy of Sciences was offering a $500 prize for the best unpublished paper on the topic of solar and stellar energy. So Bethe withdrew the CNO cycle paper and sent it in to the New York Academy of Sciences. It won the prize, and Bethe gave Marshak $50 finder’s fee and used $250 to release his mother’s furniture. The paper was subsequently published in the Physical Review in March. It was a breakthrough in the understanding of the stars, and would win Bethe the Nobel Prize in Physics in 1967. In 2002, Bethe sent a handwritten note to John N. Bahcall congratulating him on the work which won Bahcall the 2002 prize, which showed that the CNO cycle accounts for about 7% of the Sun’s energy.