Abstract
The Atomic Nuclei, Elementary Particles and the Nature of Matter Nuclear physics emerged as a new independent science when, ten years ago, Cockcroft and Walton, working on a suggestion by Rutherford, first used protons artificially accelerated to immense velocities for bombarding other heavier atoms. Before that time, work of this kind had only been done with the help of radioactive substances, atoms of which are transmuted spontaneously without any outside agent, with the expulsion of alpha-particles (that is, helium nuclei) or beta-particles (fast electrons). These alpha- and beta-particles can be used to transmute artificially stable atomic nuclei. This method still has its value, and with its help (by bombarding beryllium with alpha-particles emitted in the natural radioactive disintegration of polonium) it was shown that besides protons (hydrogen nuclei) complex nuclei contain also neutrons. These are particles similar in mass to protons but having no electric charge. To obtain neutrons in the free state, nuclear physics has begun to use clusters of protons or deutons (nuclei of heavy hydrogen). These are accelerated to speeds corresponding to energies of some tens of millions of volts, by special apparatus such as the cyclotron, which was invented in the United States by E. O. Lawrence in 1930.
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FRENKEL, P. Problems of Modern Physics*†. Nature 154, 450–454 (1944). https://doi.org/10.1038/154450a0
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DOI: https://doi.org/10.1038/154450a0