Investigation of excited 0+ states populated in the 162Er(p,t) reaction




Burbadge, Christina

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University of Guelph


Interpreting the nature of excited states in well-deformed nuclei has been an ongoing challenge in our understanding of nuclear structure. Some of the approaches that have been implemented to interpret the occurrence of low-lying excited 02+ states include vibrational excitations in β-phonons and γ-phonons, as well as pairing excitations. A further complication is the presence of shape coexistence which can increase the number of low-lying states, and if the shapes undergo mixing, the spectroscopic signatures can become ambiguous. An example of such a case is in the rare-earth region, where there is a rapid change in the ground state shape from N = 88 to N = 92. One of the difficulties in resolving the nature of these states is that there is a paucity of data, particularly for excited 0+ states, in the rare earth region. Two-neutron transfer reactions are ideal for probing 0+ → 0+ transitions in deformed nuclei. One of the intriguing features of the rare-earth region are the strongly-populated 0+ states that emerge in both (p, t) and (t, p) two-neutron transfer reactions that have been interpreted as signatures of shape coexistence and pairing isomerism. In the present work, excited 0+ states have been studied via the 162Er(p, t)160Er reaction at the Maier-Leibnitz Laboratory in Garching, Germany using 22 MeV and 24 MeV proton beams and the reaction products were momentum-analyzed with the Q3D magnetic spectrograph. In this work, sixty-nine levels were observed and angular momenta were assigned for thirty-eight of these states. In total, seven excited 0+ states were assigned, six of which were unknown until the present work and one of which was not definite. The cross sections of these low-lying excited 0+ states, with the 02+ state population around 18% of the ground state strength, suggests a special character for this state which is inconsistent with a β-vibration interpretation. The similarity of the population of the 02+ state in 160Er with low-lying 0+ states in N = 90 isotones suggests that the nature of these excitations are quite similar, with the possibility that the 02+ state is an example of shape coexistence. Results of the relative population of the excited 0+ states in 160Er will be presented, and placed into context with similar experiments in the N = 90 region.



Shape coexistence, Transfer Reactions