In-beam gamma-ray studies of neutron-rich N$\sim $20 nuclei in fragmentation reactions

Neutron-rich sodium, neon, and fluorine nuclei were produced in a two-step fragmentation/knockout experiment conducted at Michigan State University. A 140 MeV/A $^{48}$Ca primary beam bombarded a $^{9}$Be target to produce a ``cocktail'' of secondary beams ($^{29}$Na/$^{30}$Mg/$^{32}$Al and $^{32}$Mg/$^{33}$Al/$^{35}$Si). The secondary beams underwent fragmentation/knockout reactions on a second $^{9}$Be target located at the center of the Segmented Germanium Array (SeGA), which was used to measure the prompt gamma-ray decays tagged to specific fragments detected at the S800 focal plane. New high quality data on a range of nuclei were obtained, e.g. $^{30,31}$Na, $^{28,29,30}$Ne, and $^{25,26}$F. In $^{30}$Na, for example, we observed seven gamma-ray transitions and the statistics allowed the study of gamma-gamma coincidences. These data will provide new information on the structure of these exotic nuclei and specifically the role of collective degrees of freedom and the strong n-p spin-isospin interaction.