Abstract:
Background: In the A≈50 mass region M1 spin-flip transitions are prominent around 9 MeV. An accumulation of 1- states between 5 and 8 MeV generating additional E1 strength, also denoted as pygmy dipole resonance, has been established in many nuclei with neutron excess within the last decade. Purpose: The γ-decay behavior of J=1 states has been investigated in an NRF experiment. M1 excitations have been compared to shell model calculations. Methods: J=1 states were excited by quasi-monoenergetic, linearly polarized γ-ray beams generated by laser-Compton backscattering at the HIγS facility, Durham, NC, USA. Depopulating γ rays were detected with the multidetector array γ3. Results: For eleven beam-energy settings the γ-decay behavior of dipole states was analyzed by a state-to-state analysis and average γ-decay branching ratios have been investigated. 34 parity quantum numbers were assigned to J=1 states. Conclusions: Six 1- states and two 1+ states have been investigated in NRF experiments for the first time. The M1 strength distribution is in good agreement with shell-model calculations.
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