Supersymmetry in the spectra of complex atomic nuclei

Abstract

Evidence is observed for the existence of supersymmetry from the study of the odd-odd nucleus 196Au using the 19VAu (d, t), 197Au(p, d) and 19SHg(d, a) transfer reactions [1] and combining this with recent information from 77 correlatrion studies [2]. High resolution 196pt(p, d)195Pt and 196pt(d, t)195pt transfer experiments performed in parallel yielded at the same time an improved level scheme of 195pt [3]. Using extended supersymmetry, a single fit of the six parameter eigenvalue expression yielded a complete description of all observed low-lying excited states in the four different nuclei forming the supermultiplet. The detailed comparison of the transfer amplitudes for the states up to 500 keV in the odd-odd member of the supermultiplet 196Au using a semi-microscopic transfer operator provides evidence that this description is correct.Symmetry is an important concept in physics. In finite many-body systems it appears as time reversal, parity and rotational invariance but also in the form of dynamical symmetries. Among all mesoscopic systems the atomic nucleus forms one of the best testing grounds for the use of symmetry concepts because a wealth of experimental spectroscopic information can be obtained. In the field of dynamical symmetries a remarkably versatile model was elaborated in the mid seventies by Arima and Iachello [4]. This Interacting Boson Model considers 2N valence nucleons which are coupled to N nucleon pairs, as s (l = 0) and d (l = 2) bosons. The eveneven nucleus is then described in a space spanned by the irreducible representation (irrep) IN] of UB(6). The model turned out to be very successful for medium-heavy and heavy nuclei.For the description of odd-A nuclei, a fermion needs to be coupled to the N boson system. This can be done by a semi-microscopical approach which relies on seniority in the nuclear shell model [5]. An alternative to this interacting bosonfermion approach is the construction of hamiltonians exhibiting dynamical BoseFermi symmetries that are analytically solvable. In both approaches, the bosonfermion space is spanned by the irrep [g] x [1] of UB(6) | UF(M) where M is the dimension of the single particle space. A further step towards unification was made in the early eighties when Iachello and coworkers embedded the Bose-Fermi symmetry into a graded Lie algebra U(6/M) [6,7]. The supersymmetric irrep [H},