Abstract
The nature of low-lying levels in was investigated in the cold neutron-capture reaction. The combination of the high neutron flux from the research reactor at the Institut Laue-Langevin and the high -ray detection efficiency of the EXILL setup allowed the recording of coincidences. From the coincidence data precise branching ratios were extracted. Furthermore, the octagonal symmetry of the setup allowed angular-distribution measurements to determine multipole-mixing ratios. Additionally, in a second measurement the ultra-high resolution spectrometer GAMS6 was employed to conduct lifetime measurements using the gamma-ray induced Doppler-shift technique (GRID). The confirmed strong component in the decay strongly supports the assignment of the level at as low-lying isovector octupole excitation. Microscopic calculations within the quasiparticle phonon model confirm an isovector component in the wave function of the level, firmly establishing this fundamental mode of nuclear excitation in near-spherical nuclei.
- Received 14 June 2018
- Revised 25 September 2018
DOI:https://doi.org/10.1103/PhysRevC.99.011304
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