The neutron hypothesis

Iwanenko’s tentative suggestion that the neutron might be a constituent of the nucleus is certainly one of the more curious contributions to this feature. It was published in 1932, just two months after “Dr. J. Chadwick’s explanation of the mysterious beryllium radiation” that marked the discovery of the neutron (see Chadwick’s discovery of the neutron). Although he was wrong about “nuclei electrons being all packed in a-particles or neutrons”, Iwanenko hit the target as he mused that the neutron may be an elementary particle “something like protons and electrons” with “a moment ½”.
Nature 129, 798 (1932)
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The Neutron Hypothesis

Dr. J. Chadwick's explanation of the mysterious beryllium radiation is very attractive to theoretical physicists. Is it not possible to admit that neutrons play also an important rôle in the building of nuclei, the nuclei electrons being all packed in a-particles or neutrons? The lack of a theory of nuclei makes, of course, this assumption rather uncertain, but perhaps it sounds not so improbable if we remember that the nuclei electrons profoundly change their properties when entering into the nuclei, and lose, so to say, their individuality, for example, their spin and magnetic moment.

The chief point of interest is how far the neutrons can be considered as elementary particles (something like protons or electrons). It is easy to calculate the number of a-particles, protons, and neutrons for a given nucleus, and form in this way an idea about the momentum of nucleus (assuming for the neutron a moment ½). It is curious that beryllium nuclei do not possess free protons but only a-particles and neutrons.

D. IWANENKO.

Physico-Technical Institute, Leningrad, April 21

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