Decay of quadrupole-octupole 1-states in Ca 40 and Ce 140
© 2016 American Physical Society. Background: Two-phonon excitations originating from the coupling of two collective one-phonon states are of great interest in nuclear structure physics. One possibility to generate low-lying E1 excitations is the coupling of quadrupole and octupole phonons. Purpose: In this work, the γ-decay behavior of candidates for the (21+ - 31-)1- state in the doubly magic nucleus Ca40 and in the heavier and semimagic nucleus Ce140 is investigated. Methods: (γ - ,γ′) experiments have been carried out at the High Intensity γ-ray Source (HIγS) facility in combination with the high-efficiency γ-ray spectroscopy setup γ3 consisting of HPGe and LaBr3 detectors. The setup enables the acquisition of γ-γ coincidence data and, hence, the detection of direct decay paths. Results: In addition to the known ground-state decays, for Ca40 the decay into the 31- state was observed, while for Ce140 the direct decays into the 21+ and the 02+ state were detected. The experimentally deduced transition strengths and excitation energies are compared to theoretical calculations in the framework of EDF theory plus QPM approach and systematically analyzed for N=82 isotones. In addition, negative parities for two J=1 states in Ca44 were deduced simultaneously. Conclusions: The experimental findings together with the theoretical calculations support the two-phonon character of the 11- excitation in the light-to-medium-mass nucleus Ca40 as well as in the stable even-even N=82 nuclei.
Derya, V; Tsoneva, N; Aumann, T; Bhike, M; Endres, J; Gooden, M; Hennig, A; Isaak, J; Lenske, H; Löher, B; Pietralla, N; Savran, D; Tornow, W; Werner, V; Zilges, A
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