I study experimental nuclear structure with students primarily during summers. Experiments that probe nuclear structure are generally done at large accelerator facilities. We do our experimental work at the accelerator facilities at Florida State University (FSU) and the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University.
We study shell structure by measuring proton and neutron contributions to collective excitations. Collective excitations are excited states in which many protons and neutrons participate. The cartoon at right is an illustration of a collective quadrupole shape vibration, a common low-lying collective excitation. In the simplest collective picture, the nucleus us an incompressible "liquid drop" which undergoes collective shape vibrations and rotations. This purely collective model predicts equal proton and neutron contributions to excitations. However, the nuclear shell model, which focuses on single particle behavior, predicts that protons and neutrons can be trapped in closed shells and that valence nucleons dominate low-lying excited states. Hence, differences between proton and neutron behavior in collective excitations are evidence of underlying shell structure.
