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What happened to nuclear electrons?

By Hamish Johnston at the 2013 CAP Congress in Montreal

Sometimes I think that physicists can dwell too much in the past. Scientific papers, for example, often begin with a potted history of the field and it’s only in the second page that something new is mentioned.

But the Italian–Canadian physicist Francesco Barletta of CGEP Rimouski here in Quebec thinks that the physics community can often completely forget very important aspects of its past. And after seeing his fascinating talk today about the rise and fall of the “nuclear electrons” model of the nucleus, I have to agree.

I like to think I know a thing or two about physics. But just like most others in the audience, I had never heard of the theory. However, it was a leading concept of nuclear physics before the discovery of the neutron in 1932.

The theory sought to explain why the masses of nuclei did not scale with their charge. The basic idea was that a nucleus could contain one or more electrons, which offset the positive charge of one or more protons. This seemed reasonable because physicists knew about electrons and protons at the time.

Barletta explained how the theory came about and, much more interestingly, how it was dismantled piece-by-piece by subsequent experimental and theoretical breakthroughs in nuclear physics.

I’m sure I was not the only one in the audience wondering which leading theories of today will be getting similar treatment in the history lectures of tomorrow.

A great example of the debate is this paper that appeared in Physical Review and discusses the spin (or lack of spin) of nuclear electrons.

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One comment to What happened to nuclear electrons?

  1. John Duffield

    The theory wasn’t as bad as it might sound. Take a look Yakuwa’s 1935 paper, then at elements and isotopes, and you realise that you could reasonably call the residual strong force “neutron linkage”. Especially since in normal hadrons the gluons are virtual, as are the inter-hadron pions. One neutron will link two protons together, but not three.

    Now imagine you’ve got a nucleus. Get out your gedanken tweezers, and pull out a neutron. Put it down on the kitchen worktop like it’s one of those kid’s jumping poppers. Wait for it, wait for it, and POP, Beta decay. An antineutrino flies away, and you’re left with a proton and an electron. They’re not virtual.


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