Isospin character of low-lying states in ⁵⁶Fe

Low-lying states in ⁵⁶Fe, up to an excitation energy of about 4 MeV, have been investigated by means of inelastic proton and deuteron scattering experiments at E_p=65 and 400 MeV and at E_d=56 MeV, respectively. Measured cross sections and analyzing powers have been compared with coupled-channels calculations using collective form factors; calculations in both the Schrödinger and Dirac formalisms have been carried out for the proton data. For each probe, the matrix elements have been deduced for transitions from the ground state and from the 2⁺₁ state to six quadrupole (2⁺) states to one octupole (3^-₁) and two hexadecapole (4⁺₁ and 4⁺₂) states. The obtained matrix elements and the previous values from y decay or electron inelastic scattering have been used to evaluate the isospin character of the transitions. To discuss the quadrupole mixed-symmetry states in ⁵⁶Fe, the deduced neutron (M_n) and proton (M_p) components of the matrix elements, or equivalently the isoscalar (M_s) and isovector (M_v) parts, have been compared with theoretical calculations based on the neutron-proton interacting boson model and on the shell model evaluated in a full f-p configuration space.