REGULARITIES INVOLVING ⁶₉He AND ⁴₉He AND THEIR POSSIBLE IMPLICATIONS FOR NUCLEAR STRUCTURE

Abstract

An examination of several types of evidence (systematics of stable isotopes, relative abundances of isotopes, energies of excited states, neutron and proton separation energies, mass excess and binding energy, and the half-lives of long-lived heavy alpha-active nuclei) reveals regularities associated with increases in the ⁵ ₂He sub-units as well as the more familiar ⁴ ₂He (alpha-particle) sub-unit. Several ⁵ ₂He regularities involve seven, but never more, participants. This corresponds to a total range of 36A and 12Z. A consideration of the regularities leads to the suggestion that if clusters occur on the nuclear surface—or perhaps within the structure—both ⁵ ₂He and ⁵ ₂He should be considered as possible clusters. On the basis of this assumption, a threefold division of nuclei with respect to Z and N is suggested:

(i) The ⁴ ₂He region. Up to Z = N = 20

(ii) The transition region. Between Z = N = 20 and N = 50

(iii) The ⁵ ₂He region. N = 50 to N = 152.

If it is assumed that heavy nuclei (N > 50) of a given type are ‘built’ by adding ⁵ ₂He clusters to the nuclear surface, the rate of increase of N-Z is a little too rapid for stability to be maintained over a large range of Z and an examination of the ⁵ ₂He regularities leads to the suggestion that one function of N = 82 and certain other significant neutron numbers may be to reduce neutron excess.