Abstract
ATOMIC projectiles have been used by many investigators to batter down the defences which have guarded so well the innermost mysteries of the structure of matter. The a-particle, liberated spontaneously in radioactive transformations, has, thanks to its enormous velocity, been of special service in elucidating the constitution of the atom. In these investigations no one has played a more important part than Sir Ernest Rutherford, and it is, therefore, appropriate that in the address which appears as a supplement to this issue of NATURE he should give an account of the life history of such a high-speed a-particle. When the particle is expelled from a radioactive substance, it has been proved to be the nucleus of a helium atom of mass 4 carrying two positive charges of electricity. Recent experiments by Henderson have shown how, by the successive capture of electrons, the a-particle becomes a neutral helium atom. The experiments, which were carried out by observing the deflexion of a narrow pencil of a-rays in a magnetic field, have been confirmed and extended by Sir Ernest Rutherford. It appears that not only may the doubly charged helium nucleus remove and capture an electron from the outer electron structure of the atoms in its path, but the converse change may also take place. In passing through other atoms this electron may be knocked off, and the singly charged a-particle revert back to the doubly charged type. The somewhat unexpected conclusion is reached that this process of capture and loss may repeat itself more than a thousand times in the flight of the particle. Similar considerations apply in the case of singly charged and neutral helium particles. Though the results of these encounters may be less startling than those in which disintegration of an atomic nucleus like that of nitrogen or of aluminium occurs, it seems probable that the study of these rapid interchanges of charge will yield information of great value to the theoretical physicist.
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Current Topics and Events. Nature 112, 289–292 (1923). https://doi.org/10.1038/112289a0
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DOI: https://doi.org/10.1038/112289a0