A systematic study of neutron-rich even-even Fe isotopes with a neutron number from 32 to 42 is carried out by using the projected shell model. Calculations are performed up to the spin $I=20$ state. Irregularities found in the yrast spectra and in $B\hspace{0.5em}(E2)$ values are discussed in terms of neutron excitations to the high-$j$ orbital $g_{9/2}$. Furthermore, the neutron two-quasiparticle structure of a low-$K$ negative-parity band and the proton two-quasiparticle structure of a high-$K$ positive-parity band are predicted to exist near the yrast region. Our study reveals a soft nature for the ground state of $N\approx 40$ isotopes and emphasizes the important role of the neutron $g_{9/2}$ orbital in determining the structure properties for both low- and high-spin states in these nuclei.

• Received 1 September 2009

DOI:https://doi.org/10.1103/PhysRevC.80.054306