Investigating the Structure of Exotic Nuclei with Lifetime Measurements of Excited Nuclear States

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The aim of the project is the investigation of the evolution of nuclear structure far from the valley of stability from absolute transition strengths. The latter will be determined from level lifetimes which will be measured with the recoil distance Doppler-shift method (RDDS). The main focus of this work lies on the appearance of collectivity in the close vicinity of nuclear (sub-)shell closures and on changes in the shell structure of nuclei with extreme ratios of protons and neutrons leading, e.g. to shape coexistence. Such phenomena were already found in several exotic nuclei and investigated successfully in the last project of our group and also within another project. The present grant application aims for a continuation of this successful work to extend the existing data significantly and, therefore, to achieve a general picture in different mass regions missing so far and spanning from neutron-rich nuclei close to the Z = 28 shell closure to neutron deficient nuclei around shell closures at Z=50 and Z=82. As a continuation of another project we aim to examine the structural evolution of light neutron rich nuclei around Z=28 and close to exotic doubly-magic 78Ni by investigating odd 59,61,63Mn and 75−79Cu. Further, the neutron deficient isotopes 112,116Te are in the focus of our interest: we want to solve the conundrum that even the transition strengths between the lowest yrast states cannot be explained with model approaches so far. However, new shell model calculations for the neighboring Sn isotopes in a very large valence space performed by the group of T. Otsuka were able to reproduce E2 transition strengths for the first time that could not be understood before. Here we plan to perform similar calculations for the Te isotopes in collaboration with T. Otsuka to solve the aforementioned conundrum and answer the question, if proton excitations over the Z=50 shell closure can explain the observations, similar to Pt and Hg isotopes (excitation over the Z=82 shell closure). We also aim to measure yrast transition strengths in 174,178W and 176Pt as existing experimental data are contradictory and do not allow a conclusion on the structure, e.g., with respect to an expected shape coexistence in 176Pt.