July 02 – Birth of Hans Bethe (1906)

The happy chap in the photograph is today’s birthday boy, German-born (later American) nuclear physicist, Hans Bethe.

Hans Bethe
Hans Bethe

Born in Strasbourg in 1906, Bethe majored in chemistry at Strasbourg University for a while, but was tempted to Munich in 1926 by the superior standard of physics there. After obtaining his doctorate, Bethe took up a couple of posts in Germany, before obtaining a traveling scholarship from the Rockefeller Foundation. This enabled him to work at the Cavendish Laboratory in Cambridge, and then for Enrico Fermi in Rome. A year in Manchester was followed by Bethe taking up a post at Cornell University in 1935.

Like many eminent nuclear physicists of the 1940s, Bethe was involved in the development of the atomic bomb, and later the H-bomb (although he claimed to be opposed to it).

From our perspective, though, it is Bethe’s work on theoretical astrophysics that gets his photo at the top of this page. In 1967 he was awarded the Nobel Prize in Physics, and his work on the thorny problem of how electron neutrinos convert to muon neutrinos is remarkable, and even more so when one considers that he was in his 80′s at the time.  Muons, despite the protestations of my Ubuntu spellchecker, do exist, but only for a tiny fraction of a second.  They are like electrons, but with a greater mass. Muons are leptons (a word my spellchecker is happy with).

Basically, the so-called solar neutrino problem was a discrepancy between the number of electron neutrinos passing through the Earth and the number predicted by models of the Sun’s interior. I don’t think we need go into it too much, but the solution was that supposedly massless neutrinos aren’t massless after all, and can change from one type to another.

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