U(9) symmetry in the interacting boson model

Further generalization of boson phenomenology is conducted for removing dimerits of an interacting boson model (MIB) presupposing that the model does not permit to describe low-lying collective levels of negative parity of even-even nuclei. The mentioned shortcomings of the model are excluded by introduction of the so-called p-bosons alongside with s- and d-bosons. At the same time np-forces between nucleons are taken into account. A structure of energy spectra of nuclei for some representations of SU(3)-symmetry belonging to completely symmetric representation of U(9)-group is considered in a modified MIB. Spectra of well studied experimentally 228Th and 238U are considered in detail. The calculated spectra reproduce structures of levels observed in the experiment. 228Th nucleus displays bands of negative parity not described by an ordinary Sd-boson model. The same is observed for 238U spectrum. Thus, hypothesis on existence of p-bosons results in a rather simple method for description of low-energy collective states of atomic nuclei