Advanced microscopic IBM1 version: Description of the crossing of bands in Th isotopes

The boson representation of fermion operators is used. A method is described for calculating the parameters of boson operators based on consideration of matrix elements between phonon states with a minimum number of the latter. The configuration space of bosons is expanded up to bosons with multipole [Formula: see text]. Within the framework of this method, the possibility of implementing backbending in even isotopes [Formula: see text]Th is considered. This effect is reproduced in accordance with experimental data only for the lightest of these nuclei. The intersection of bands is obtained only for two nuclei. Moreover, for [Formula: see text]Th it is so smooth that it does not appear through the moment of inertia. Among the properties, the energies of the yrast bands and the values of [Formula: see text] are considered.