Published online by Cambridge University Press: 24 October 2008
1. The theorem of quantum mechanics that “the spin part of the angular momentum is approximately a constant of motion provided that the forces depending on the direction of the spins are small compared with the total interaction forces” is introduced into the discussion of artificial nuclear transformations. A definition is given for the terms “probable” and “not probable” nuclear reaction.
2. Attention is drawn to the experimental result that the reaction Li6 + H1 → He4 + He3 is more probable than the reaction Li7 + H1 → 2He4, and an explanation is suggested.
3. The nuclear spin of Lie is derived from nuclear transformations and found to be 1.
4. Similar derivations for the spins of H3, He3 and B11 are summarised in a table.
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∥ [Note added in proof: If, however, one of the α-particles in reaction (2) remains in an excited state with L = 1 and S = 0 or 1, the reaction would not be “forbidden” for l 1 = 0. These excited states might give rise to the γ-rays observed by Crane and Lauritsen (reported in the International Conference on Physics) when bombarding Li with 900kV-protons. If the excitation energy is nearly the total energy available in the disintegration there will be a small probability that the particles will break up (because of their mutual potential barrier) and the probability of getting excited α-particles will rise steeply as the energy of the bombarding, protons is increased until the relative energy of the α-particles (with one in an excited state) surmounts the top of the barrier of their mutual potential.]
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