Nuclear Structure of Neutron Rich 34P Using in-Beam Gamma Ray Spectroscopy

Increasing dominance of negative parity intruder states in neutron-rich nuclei in the sd shell as N approaches 20 shows evidence of evolving shell structure. Systematically examining the structure of isotopes with increasing N while filling the vd3/2 level highlights a large number of intruder configurations. These intruder configurations come from the decrease in energy to promote a neutron across the N = 20 shell gap. Such studies are needed to help in the refinement of the shell model and increase its predictive power for nuclei far from stability. The presented work chronicles a series of 18O(18O,pn) experiments conducted around the world to study high spin states in 34P, a nucleus in the sd shell bordering the "island of inversion." One of these experiments which was conducted at Argonne National Laboratory where a 24 MeV neutron rich 18O beam impinged on a Ta backed 18O target, is presented here in great detail. The evaporated charged particles were detected with MICROBALL while the γ rays emitted were detected with GAMMASPHERE. A brief discussion of the theory of analysis techniques used in in-beam γ-ray spectroscopy is presented followed by an in depth discussion of the analysis of this experiment. From the analysis of excited states populated in 34P, a number of candidate states including 0p0h and 1p1h configurations are found and identified. A few states are also observed that have strong evidence pointing towards a more exotic 2p2h configuration. One state, the highest ever observed in 34P at 7917 keV may even be of the extremely exotic 3p3h type though the evidence is very speculative. Spins and parities of all levels have been assigned through arguments based on lifetime measurements of individual states measured with Doppler shift attenuation techniques and full γ-ray angular distributions whenever possible. Model dependent assignments have also been used in some spin assignments. In total, 10 newly observed levels are presented along with 23 newly observed transitions. Detailed shell model calculations using both the WBP - a and sdpfnow interactions are also presented. A comparison of theoretically predicted properties of individual states, including occupations, branching ratios and electromagnetic transition strengths is made to the experimentally observed states when applicable. Both interactions show fairly reliable predictive power for the both 0p0h and 1p1h configurations with an approximate root mean squared deviation of 150 keV in energies. States involving 2p2h configurations are discussed, though the current shell model calculations are much less reliable for them.