Abstract
The idea of the Interacting Boson Approximation (IBA) by Arima and Iachello simplified the description of low lying collective states enormously [1, 2]. Now it became relatively easy to reproduce the experimental observables in a wide variety of nuclei ranging from spherical to well deformed [3]. Further improvement was achieved when proton- and neutron-bosons were distinguished explicitly in the 1BA-2 [4]. In the early eighties Iachello used the IBA-2 to predict a new class of states which are not fully symmetric under the exchange of protons and neutrons. In axially deformed nuclei the lowest lying member of these states should be a collective 1+-state around 2 – 4 MeV excitation energy [5]. The experimental finding of this so called “scissors mode” in electron scattering experiments by a group around A. Richter from Darmstadt [6] was an impressive proof for the power of the IBA-2. Whereas the original IBA-models with s- and d-bosons (representing bosons with Jπ=0+ and Jπ=2+) were only capable of describing positive parity states, the model can be extended in a natural way to allow the description of negative parity states by including a p-boson with Jπ=1- and a f-boson with Jπ=3- [7–10] The investigation of negative parity states will be the subject of this contribution.
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von Brentano, P., Zilges, A., Zamfir, N.V., Herzberg, R.D. (1994). Low Lying Electric Dipole Excitations and the Interacting Boson Model. In: Gruber, B., Otsuka, T. (eds) Symmetries in Science VII. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-2956-9_12
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