Microscopic description of low-lying M1 excitations in odd-mass actinide nuclei

Abstract A restoration method of a broken symmetry which allows self-consistent determination of the separable effective restoration forces is now adapted to odd-mass nuclei in order to restore violated rotational invariance (RI-) of the Quasiparticle Phonon Nuclear Model (QPNM) Hamiltonian. Because of the self-consistency of the method, these effective forces contain no arbitrary parameters. Within RI-QPNM, the properties of the low-lying magnetic dipole excitations in odd-mass deformed 229–233 Th and 233–239 U nuclei have been investigated for the first time. It has been shown that computed fragmentation of the M 1 strengths below 4 MeV in these nuclei is much stronger than that in neighboring doubly even 228–232 Th and 232–238 U nuclei. For 235 U the summed M 1 strength in the energy range 1.5–2.8 MeV is in agreement with the relevant experimental data where the missing strength was extracted by means of a fluctuation analysis.