In-beam γ -ray spectroscopy of Mn 63

Background: Neutron- rich, even- mass chromium and iron isotopes approaching neutron number N = 40 have been important benchmarks in the development of shell- model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd- mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions. Purpose: We report the observation of two new. gamma-ray transitions in Mn-63, 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-) excited states 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 Be-9 target and in the fragmentation of Fe-65.gamma gamma coincidence relationships were used to establish the decay level scheme. A Doppler line- 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- model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change. Conclusions: While the theoretical ( 7/ 2-) and ( 9/ 2-) excitation energies show little dependence on the model space, the calculated lifetime of the ( 7/ 2-) level and calculated energy of the ( 11/ 2-) level reveal the importance of including the neutron g9/ 2 and d5/ 2 orbitals in the model space. The LNPS effective shell- model interaction provides the best overall agreement with the new data.