A study of deformation in light nuclei: (I). Application to the ground state band of 20Ne and to the low-energy spectrum of 19F

Abstract

The properties of the ground state band of 20Ne are shown to be well described by the set of wave functions projected from a single intrinsic state. Particular deformed states of nuclei around 16O may be constructed by breaking up the 16O core in such a manner as to produce two protons and two neutrons in the (2s, 1d) shell. Following an observation by Christy and Fowler, the wave function for these four particles is described in terms of the ground state 20Ne band and deformed states are obtained by coupling 1p hole states on to the members of this band. The odd-parity levels of 19F are described by coupling p 1 2 and p 3 2 proton holes on to the ground state 20Ne band and it is shown that the measured E1 transitions in 19F provide evidence for states of this structure. It is also shown that the low-lying even-parity levels of 19F are well described in terms of a single K = 1 2 + band , and these states are compared directly with those obtained from a full intermediate coupling calculation. Overlaps of over 99% are obtained for the ground state ( 1 2 + ) and the 5 2 + members of the band. The structure of the K = 1 2 + band is interpreted on the basis of the nucleus having permanent P 4 as well as P 2 (Nilsson) type distortions. Electromagnetic transitions in 19F are discussed in detail and the results for the odd-parity states are compared with those of a similar calculation by Harvey in the SU 3 scheme. A detailed study of the levels in 19F in the region of 4 to 5 MeV excitation is made and the extent to which core deformation is important in the even parity states is discussed on a semi-quantitative basis. The properties of the 3.91 MeV level (possibly a doublet) are crucial to the detailed interpretation of this nucleus.