Naqvi, Farheen (2011) Probing the collectivity in neutron-rich Cd isotopes via gamma-ray spectroscopy. PhD thesis, Universität zu Köln.
The spin and configurational structure of excited states of 127Cd, 125Cd and 129Cd, having two proton and three, five and one neutron holes, respectively in the doubly magic 132Sn core have been studied. The isomeric states in Cd isotopes were populated in the fragmentation of a 136Xe beam at an energy of 750 MeV/u on a 9Be target of 4 g/cm2. The experiment was performed at GSI Darmstadt. The neutron-rich Cd isotopes were selected using the Bρ-∆E-Bρ method at the FRagment Separator (FRS). Event by event identification of fragments in terms of their A (mass) and Z (charge) was provided by the standard FRS detectors. The reaction residues were implanted in a plastic stopper surrounded by 15 Ge cluster detectors from the RISING array to detect the gamma decays. In 127Cd, an isomeric state with a half-life of 17.5(3) μs has been detected. This yrast (19/2)+ isomer is proposed to have mixed proton-neutron configurations and to decay by two competing stretched M2 and E3 transitions. Experimental results are compared with the isotone 129Sn. In 125Cd, apart from the previously observed (19/2)+ isomer, two new metastable states at 3896 keV and 2141 keV have been detected. A half-life of 13.6(2) μs was measured for the (19/2)+ isomer, having a decay structure similar to the corresponding isomeric state in 127Cd. The higher lying isomers have a half-life of 3.1(1) μs and 2.5(15) ns, respectively. Time distributions of delayed gamma transitions and gamma-gamma coincidence relations were exploited to construct decay schemes for the two nuclei. Comparison of the experimental data with shell-model calculations is also discussed. The new information provides input for the proton-neutron interaction in nuclei around the doubly magic 132Sn core. The gamma decays of the isomeric states in 129Cd were not observed experimentally. The reasons for the non-observation of delayed gamma rays for 129Cd are either an isomeric half-life of less than 93 ns based on the experimentally obtained isomeric ratios of the (19/2)+ in 127,125Cd, or an E3 spin trap emerging from shell-model calculations.
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