Mirror symmetry at mass A = 54: E4 effective charges near doubly magic $^{56}$Ni
Résumé
Proton-emission branches of the isomer in the nucleus 54Ni have been imaged with the active target and time projection chamber (ACTAR TPC) in an experiment conducted at the Grand Accélérateur National d'Ions Lourds (GANIL). The completed decay scheme allows derivation of the reduced transition strengths, and , for the two competing γ-ray transitions. By means of a comparison with their well-known ‘mirror transitions’ in 54Fe, and aided by a variety of shell-model calculations in the fp model space, effective charges for E4 transitions near 56Ni can be deduced: and . Mirror-energy differences are explored with various shell-model interactions and isospin-symmetry breaking terms.