Macroscopic and microscopic aspects of superdeformed atomic nuclei in the A∼190 region from feeding and decay measurements.

摘要

Superdeformed (SD) excitations in 195Pb and 198 Po have been populated with heavy-ion fusion-evaporation reactions at the 88-Inch cyclotron facility at Lawrence Berkeley National Laboratory and the γ-ray spectroscopy was studied using the Gammasphere array. Feeding and decay of superdeformed states in 195Pb and 198Po have been studied. The quasicontinuous (QC) decay of SD excitations in 195Pb have been extracted. The shape of the QC decay spectrum is consistent with at least a two step process with no gap in the level density of normal deformed (ND) excitations at finite temperature and spin. From the QC decay spectrum the SD excitation energy relative to ND states is greater than 2.5 MeV at 13/2ħ has been deduced. The intensity attenuation of the in-band transitions of SD 195Pb caused by the decay of SD excitations suggest a well depth of 2 MeV at N10ħ with a slight spin dependence. Results show that the decay occurs via the favored signature of the 5/2[752] orbital.; Energy-spin matrices associated with SD and ND excitations in 198Po have been extracted. The energy-spin entry distributions associated with SD excitations in 198Po show that the highest spin feeding SD 198Po is roughly 30ħ and on average is 21ħ. The SD excitation energy of 4 MeV at zero spin has been deduced by observing the lowest limits of the entry distribution and using the SD yrast line to extrapolate to spin zero. Analysis of the discrete in-band transitions associated with 198Po show that the mixing between ND states and SD states is greater than 36% at 8ħ. The intensity attenuation of the in-band transitions of SD 198Po, caused by the decay of SD excitations, suggest a well depth of 2 MeV at ∼10ħ with a slight spin dependence, and is consistent with the energy-spin entry distributions associated with SD excitations.