### Speaker

Liam P. Gaffney
(University of Liverpool)

### Description

There is considerable theoretical and experimental evidence that atomic nuclei can assume reflection asymmetric shapes that arise from the octupole degree of freedom. From a microscopic point of view, the wave functions of low-lying 3- octupole excitations must contain components which include the intruding unique parity state ( _l_ , _j_ ). Because of the nature of the octupole-octupole interaction in nuclei, strong octupole correlations arise when the Fermi level lies between this intruder subshell and a subshell with Δ _j_ , Δ _l_ =3, giving rise to [ _l_ , _j_ ; _l_ -3, _j_ -3] particle-hole configurations at relatively low excitation energies. The strongest correlations occur near the proton numbers _Z_ = 34, 56 and 88 and the neutron numbers _N_ = 34, 56, 88 and 134 where, for the heaviest nuclei, an octupole deformation can occur in the ground state. Indeed, at these values of _Z_ and _N_ , nuclei exhibit phenomena associated with reflection asymmetry such as odd-even staggering of the positive- and negative-parity yrast bands in even-even nuclei, parity doublets in odd mass nuclei, and enhanced _E_ 1 moments due to a division of the centre of charge and centre of mass. The only observable that provides unambiguous and direct evidence for enhanced octupole correlations in nuclei is the _E_ 3 matrix element, and the measure of octupole correlations in the ground state is the B( _E_ 3; 0+ → 3-). In the mass region where octupole correlations are expected to be largest, i.e. at _Z_ = 88 and _N_ = 134, there is a lack of spectroscopic data on _E_ 3 moments. So far, only for 226Ra, with its comparatively long half life of 1600 years, has it been possible to measure the B( _E_ 3) strength using Coulomb excitation. This talk will present the current status and the first results from the recent Coulomb excitation the post-accelerated 224Ra beam at REX-ISOLDE facility, CERN, using the MINIBALL setup.

### Primary author

Liam P. Gaffney
(University of Liverpool)

### Co-authors

Butler Peter A.
(University of Liverpool)
Scheck Marcus
(University of Liverpool)