Nuclei in certain regions of the nuclear chart can change properties as a function of the number of neutrons or protons they contain. Such structural changes often correspond to shape changes from, say, spherical to ellipsoidal. Recent experimental evidence has suggested that such shape changing regions can be viewed as phase transitions, and can exhibit phase coexistence ( of spherical and ellipsoidal shapes). Here, one might think that the "control parameter" of the phase transition would be the neutron number. However, since nuclei are finite systems and since the neutron number is an integer, a surrogate for neutron number has been proposed. Much new experimental data on such nuclei has verified this picture and led to the proposal of a new class of symmetries called "Critical point symmetries", of which two types are known and have been discovered empirically. This talk will focus on these issues and their implications for our understanding of nuclear structure, of the origin of deformation and collectivity in nuclei, and will touch on applications to other physical systems.
ANL Physics Division Colloquium Schedule