Speaker
Dr
Magda Zielinska
(CEA Saclay)
Description
Shell evolution in the vicinity of 68Ni has recently attracted many theoretical and experimental investigations. By now it has been clearly established that the presumed subshell closure at N=40 is not very pronounced. While the intruder character of the 1g9/2 and 2d5/2 neutron orbital induces collectivity by pair excitations from the fp shell into the g9/2 orbital, the parity change hinders quadrupole excitations and therefore mimics the properties of a doubly magic nucleus in 68Ni, i.e., a high 2+1 energy and a low B(E2; 2+ → 0+) value. Adding valence nucleons to the N=40 open shell leads to a rapid increase of collectivity, with an interplay of both collective and single-particle degrees of freedom. Such rapid changes indicate underlying complex effects and make this region ideal for testing theoretical calculations.
While measurements of B(E2; 2+→ 0+) values are useful to investigate the evolution of collectivity along isotopic chains, even more insight into the collective behavior can be gained by measuring lifetimes of higher-lying states. Almost all stable Zn isotopes present an anomalously low B(E2; 4+ → 2+)/ B(E2; 2+ → 0+) ratio of 1 or less, which is normally observed only around closed shells. Coulomb excitation studies at ISOLDE (74,76Zn [1]) as well as a DSAM lifetime measurement in 70Zn [2] suggested an important increase of collectivity of the 4+ state for heavy Zn isotopes with a maximum at N=40. However, a recent RDDS lifetime measurement performed with AGATA Demonstrator in Legnaro [3] yielded lifetimes of the 4+ states in 70-74Zn that are considerably longer and correspond again to B(E2; 4+ → 2+)/ B(E2; 2+ → 0+) ratio lower than 1. This has been confirmed by the results of another RDDS measurement performed at GANIL [4] for 70,72Zn.
The observed discrepancy between lifetime and Coulex data triggered further measurements of transition probabilities in heavy Zn isotopes. In order to decide between the two experimental values of B(E2; 4+ → 2+) in the heaviest stable zinc isotope 70Zn, a dedicated Coulomb excitation measurement was carried out at HIL Warsaw. Very recently, Coulomb excitation studies of neutron-rich 74,76Zn nuclei were performed at HIE-ISOLDE as the very first experiment at this facility. Preliminary results from Coulex analysis and future perspectives will be discussed.
[1] J. Van de Walle et al., Phys. Rev. C79 (2009) 014309
[2] D. Muecher et al., Phys. Rev. C79 (2009) 054310
[3] C. Louchart et al, Phys. Rev. C87 (2013) 054302
[4] I. Celikovic et al, Acta Phys.Pol. B44, 375 (2013)
Primary author
Dr
Magda Zielinska
(CEA Saclay)
Co-authors
Dr
Andrés Illana Sisón
(KU Leuven)
Dr
Elisa Rapisarda
(PSI Villigen)
Prof.
Piet Van Duppen
(IKS-KULeuven - CERN-ISOLDE)
