The Quadrupole Moment of 133La and Shape Isomerism

Abstract

I am going to talk about some work which shows evidence of shape isomerism in 133La. This evidence is based partly on the measurement of the quadrupole moment of the 3/2− level at 535.4 keV. It is important to note that this energy is low compared to that which might be expected according to either the spherical shell model or the Nilsson model, provided one uses a reasonable deformation parameter. Furthermore, it is important to note that the low lying states of 133La all have positive parity except for the 535.4 keV level. Similarly, all the low lying states are understood in terms of the spherical shell model with one exception, viz. the 535.4 keV level. In order to explain the 3/2− level, we need to use Nilsson orbitals with huge deformation. We will come back to this point in another context later.