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1-2: Hydrogen and Helium Nucleus

[Nucleus of the Hydrogen Atom = Proton]
Rutherford thought that the nucleus of the lightest atom, i.e. hydrogen nucleus, is one of the fundamental particles in the Nuclear World, i.e. the World of the Atomic Nucleus. He named this particle "proton", because Greek proton means "first".
Namely, the proton is none other than the hydrogen ion, so that its electric charge is +e.
It was made clear by Rutherford's experiment of the artificial transmutation of elements that the proton is one of the fundamental constituents of atomic nuclei (1919).

[Nucleus of the Helium Atom = Alpha Particle]
Alpha particles emitted from the radioactive elements such as radium and polonium are doubly ionized helium i.e. the helium atom having lost two electrons. This was confirmed by Rutherford and his student, Royds, in 1908. (See the page of "Microscopic World -1-: 2-3: Scattering of Alpha Particle by an Atom").
From these investigations, it was clarified that the mass of an alpha particle is four times as large as the proton mass, and the electric charge is twice as much as that of the proton, i.e. +2e.

[What is the alpha particle made of ?]
It was clear that the proton is contained in a nucleus. Then, what are the other constituents of a nucleus? In Rutherford's days, people knew the existences of electron and proton. Then is it possible to constitute an alpha particle by combining these two kinds of particles, electrons and protons?
We may consider that the alpha particle consists of four protons and two electrons combining together with each other. This idea appears plausible enough in view of both mass and charge. However, this idea has a serious defect and is unacceptable, as will be discussed on the next page.

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