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

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 229–233Th and 233–239U nuclei have been investigated for the first time. It has been shown that computed fragmentation of the M1 strengths below 4 MeV in these nuclei is much stronger than that in neighboring doubly even 228–232Th and 232–238U nuclei. For 235U the summed M1 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.