In-beam γ -ray spectroscopy of $^{63}$Mn

The measurement was performed at the National Superconducting Cyclotron Laboratory (NSCL).International audienceBackground: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number N = 40 havebeen important benchmarks in the development of shell-model effective interactions incorporating the effectsof shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provideimportant and complementary sensitivity to these interactions.Purpose:We report the observation of two newγ -ray transitions in 63Mn,which establish the (9/2−) and (11/2−)levels on top of the previously known (7/2−) first-excited state. The lifetime for the (7/2−) and (9/2−) excitedstates were determined for the first time, while an upper limit could be established for the (11/2−) level.Method: Excited states in 63Mn have been populated in inelastic scattering from a 9Be target and in thefragmentation of 65Fe. γγ coincidence relationships were used to establish the decay level scheme. A Dopplerline-shape analysis for the Doppler-broadened (7/2−) → 5/2−, (9/2−)→ (7/2−), and (11/2−) → (9/2−)transitions was used to determine (limits for) the corresponding excited-state lifetimes.Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-modelcalculations using different model spaces and effective interactions in order to isolate important aspects of shellevolution in this region of structural change.Conclusions: While the theoretical (7/2−) and (9/2−) excitation energies show little dependence on the modelspace, the calculated lifetime of the (7/2−) level and calculated energy of the (11/2−) level reveal the importanceof including the neutron g9/2 and d5/2 orbitals in the model space. The LNPS effective shell-model interactionprovides the best overall agreement with the new data