The shell model and collective structures in54,55,56Fe

Abstract

Extensive shell-model calculations have been performed on 5'*'55'56Fe. The results obtained in a model space with two and with up to three f7/2 holes in the 56Ni core are compared with experiment. The Surface Delta Interaction (SDI) and the Kuo Brown interaction (KB) have been used to calculate energy levels, spectroscopic factors and electromagnetic properties resulting especially for 56Fe in a remarkably good agreement with experiment. Admixtures of three-hole components in the wave functions are significant and increase with mass number. Properties of high-spin states with J <15 are discussed. Pronounced collective features derived microscopically are expected in 56Fe. Finally some suggestions for interesting experiments are given.

A microscopic classification of high-spin states in 56Fe

“…For SDI the fs/2 occupation numbers are considerably larger than for KB. The experimental S-factor for pick-up on 56Fe favours the SDI value [5].…”

“…For SDI the fs/2 occupation numbers are considerably larger than for KB. The experimental S-factor for pick-up on 56Fe favours the SDI value [5].With the success of the detailed interpretation of the properties of low-lying states in 56Fe in mind, a shell-model investigation of other observables in this nucleus becomes more meaningful. Presently we would like to discuss some remarkable properties of high-spin states (J= 8-15) in 56Fe which have been obtained with the same interactions (KB and SDI) and model space as used in ref.…”

“…Presently we would like to discuss some remarkable properties of high-spin states (J= 8-15) in 56Fe which have been obtained with the same interactions (KB and SDI) and model space as used in ref. [5]. These states are interesting because one can investigate the possible appearance of collective features in the yrast region from a microscopic point of view.…”

“…Very recently large-scale shell-model calculations on positive-parity states in 54-56Fe have been performed [5]. It has been demonstrated that many properties of these isotopes can be described well in a (fT/2)m(fs/2P3/2Pl/2) n model space with m >~ 13 and n ~< 3, i.e.…”

“…up to three holes in the closed f7/2 shell have been taken into account. Two quite different effective interactions have been investigated (i) a realistic interaction derived from slightly modified [5] Kuo-Brown matrix elements (denoted by KB) and (ii) two-body matrix elements from the schematic Surface Delta Interaction [6] (denoted by SDI). In particular for 56Fe a nice one-to-one correspondence exasts between theory and experiment for all states below 4 MeV excitation energy.…”