A STUDY OF DEFORMATION IN LIGHT NUCLEI .2. APPLICATION TO EVEN-PARITY STATES OF MASS-18 NUCLEI

The properties of the low-lying even-parity levels of 18F and 18O are shown to be well understood in terms of an extended shell-model calculation in which deformed (4-particle-2-hole) states are mixed with the usual two-particle states. The properties of the levels investigated are their energies, electromagnetic decays and reduced widths. The deformed states are constructed by first forming a representation for the ground state band of 20Ne and then coupling on to this a complete set of two-hole states formed from (1p)-2 oscillator configurations. It is shown that admixtures derived from configurations which include p 3 2 holes are of much greater importance in the low-lying T = 0 states than in the T = 1 states. It is found that the observed E2 decay strengths in both 18O and 18Ne require the adoption of an effective charge of about 0.3e for their explanation. The observed E2 decays in 18F between the lower T = 0 levels, however, are well reproduced without effective charge. This feature, for which there is no explanation in terms of the normal effective charge concept, is discussed in terms of second order perturbation theory, which takes into account states in which one particle from the core is promoted through two major shells. © 1969.