Study of electric multipole transition probabilities and their importance in reaction dynamics

The atomic nucleus is a mesoscopic system that exhibits features from both quantum and macroscopic domains. Recent attempts try to model the interactions between the nucleons based on their fundamental quark compositions and involve different many-body terms. Given these considerations, one would expect the structure and interactions of the nucleus to be chaotic and complicated. However, empirical data on level schemes of stable even-even nuclei reveal that the low-lying excited states exhibit a pattern that repeats in different regions of the nuclear chart. A survey of the spin-parity of first excited states in such nuclei shows that they are predominantly 2⁺. Also, the first negative parity state in a vast majority of even-even nuclei is 3^-. The characteristic features of these states can be described by the phenomenon of collectivity, or a coherent motion of the nucleons, that can be observed in numerous even-even nuclei across the nuclear chart. Transitions to excited states are commonly expressed in terms of dynamic deformation of the equilibrium nuclear shape - such as surface oscillations for nuclei with spherical symmetry. For axially-symmetric deformations, one thinks of a neutron-proton fluid undergoing homogeneous excitations, with their transition densities in the ratio of N/Z