Question

Who discovered the proton? And how was it discoverd?

Asked by: Undisclosed Sender

Answer

In most popular texts on particle physics you see a long laundry list of particles and their discoverers :

1897 Thomson discovers the electron
1911 Rutherford discovers the nucleus
1932 Chadwick discovers the neutron

and so on and so on. Somewhere between Thomson and Chadwick, physicists realized that there are positively charged constituents of the nucleus, which we call 'protons'. The way this happened was a gradual process, and that is why it is hard to say exactly who discovered the proton, although if you had put a name against it, it would be Ruthford, sort of.

After the discovery of the electron, it was realized that there must be positive charge centers within the atom to balance the negative electrons and create electrically neutral atoms. Rutherford's discovery of the nucleus demonstrated that these positive charges were concentrated in a very small fraction of the atoms' volume. In 1919 Rutherford discovered that he could change one element into another by striking it with energetic alpha particles (which we now know are just helium nuclei). In the early 1920's Rutherford and other physicists made a number experiments, transmuting one atom into another. In every case, hydrogen nuclei were emitted in the process. It was apparent that the hydrogen nucleus played a fundamental role in atomic structure, and by comparing nuclear masses to charges, it was realized that the positive charge of any nucleus could be accounted for by an integer number of hydrogen nuclei. By the late 1920's physicists were regularly referring to hydrogen nuclei as 'protons'. The term proton itself seems to have been coined by Rutherford, and first appears in print in 1920.

An excellent reference on the history of particle physics is Abraham Pais's _Inward Bound_ (Oxford Press). Another good, and less bulky, overview of the development of particle physics is The Particle Hunters_ by Ne'eman and Kirsh (Cambridge Press).

Answered by: Dr. Lee Sawyer, Assist. Professor of Physics, Louisiana Tech Univ.

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