MULTIPARTICLE MULTI-HOLE EXCITATIONS AND NEW SYMMETRIES NEAR CLOSED SHELLS

We discuss the experimental evidence for many-particle many-hole excit ations (mp-nh) at and near to closed shells. Besides a shell-model app roach and in order to understand the salient features of the general b ehaviour of the 0(+) intruder band heads, we mainly concentrate on a g roup theoretical classification. Using the boson model, various possib ilities to classify intruder mp-nh excitations can be shown to exist. Ample evidence for the realization of these new symmetries is given in (i) the Z = 50 mass region and, in (ii) the Z = 82 Pb mass region. Fi nally, a possible extension to encompass also mp-nh excitations in lig ht nuclei is presented.