Systematic Study of Triaxial Deformation in the Relativistic Mean Field Theory

We use the relativistic mean field (RMF) theory to systematically study the change of deformation of even-even nuclei in the proton-rich Xe region. We investigate the appearance of triaxial deformation in 25 nuclei in the region covering Z=50-58 and N=64-72 by performing constrained, triaxially symmetric RMF calculations of their energy surfaces. We include pairing correlations using the BCS formalism. We find that the Sn isotopes are spherical and the Te isotopes are very gamma unstable with shallow minima around gamma = 60 degrees. Adding more protons, the Xe, Ba and Ce isotopes have prolate deformations with their sizes increasing with proton number. The neutron number dependence is found to be small. We compare the calculated results with the available experimented data on the binding energy and the radii.