Theoretical study demonstrates accurate pygmy dipole resonance predictions in N=82 isotones, indicating the interacting boson approximation captures low-energy dipole excitations.
Background: The pygmy dipole resonance (PDR) is an interesting nuclear structure phenomenon with an impact in predicting different astrophysics scenarios, for example, specific properties of neutron stars that can be determined from the thickness of the neutron skin which is directly connected to the strength of the PDR. Various collective and microscopic models were employed in order to account for the observed properties of the PDR.Purpose: Determine for the first time whether it is possible to use the interacting boson approximation (IBA) to reproduce the general characteristics of the PDR.Methods: The PDR properties of the stable even-even $N=82$ isotones are calculated in the IBA-$spdf$ model based on the assumption that many effects of the mixing caused by the shell structure can be simulated by considering the number of bosons as an effective value.Results: The IBA calculations indicate a resonance-like structure of the $E1$ strength in the energy region 5--8 MeV, thus confirming the experimental results for this mass region. The distribution and fragmentation of the J^π=1^- states and of the $E1$ strength are in good agreement with the experimental data. By employing the same procedure as for the $N=82$ isotones, the model is used to predict the PDR strength for a nucleus in a different mass region, i.e., for the ⁹⁴Mo nucleus.Conclusions: The calculations confirm a good agreement for the distribution and fragmentation of the $E1$ strength.
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Pascu et al. (2012) studied this question.
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