Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)+ state in 78Zn could be firmly established and for the first time the 2+ --> 0(1)+ transition in 80Zn was observed at 1492(1) keV. B(E2,2(1)+ --> 0(1)+) values were extracted for (74,76,78,80)Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni.
The reduced transition probabilities B(E2; 0 + g.s. → 2 + 1 , 2 + 2 ) in 70 Zn and the full B(E2; 0 + g.s. → 2 + ) strength up to Sn=7.79 MeV in 68 Ni have been determined at the LISE/GANIL facility using the Coulomb-excitation technique at intermediate beam energy on a 208 Pb target. The γ rays emitted in-flight were detected with an array of 46 BaF2 crystals. The angles of the deflected nuclei were determined in order to disentangle and extract the Coulomb and nuclear contributions to the excitation of the 2 + states. The measured B(E2; 0 + g.s. → 2 + 1 ) of 1432(124) e 2 fm 4 for 70 Zn falls in the lower part of the published values which clustered either around 1600 or above 2000 e 2 fm 4 , while the B(E2; 0 + g.s. → 2 + 2 ) of 53(7) e 2 fm 4 agrees very well with the two published values. The relatively low B(E2; 0 + g.s. → 2 + 1 ) of 301(38) e 2 fm 4 for 68 Ni agrees with previous studies and confirms a local magicity at Z = 28, N = 40. Combining the results of the low-energy spectra of 68 Ni and 70 Zn and their shell-model interpretations, it is interesting to notice that four different shapes (spherical, oblate, prolate and triaxial) are present. Finally, a summed E2 strength of only about 150 e 2 fm 4 has been found experimentally at high excitation energy, likely due to proton excitations across the Z = 28 gap. The experimental distribution of this high-energy E2 excitation agrees with SM calculations, but its strength is about two times weaker.
The knowledge of spin and parity of excited levels in exotic nuclei revealed exciting phenomena appearing only in nuclei with extreme N/Z ratios. Excited levels in nuclei are mainly depopulated by competitive processes between gamma-emission and internal electron conversion. The spin and parity of the initial and final state for a given Z and gamma energy could be deduced by knowing the ratio between the emitted conversion electrons and gamma particles. By measuring the internal conversion coefficient αk or the ratio αk/αL we can extract the multipolarity of the transition. This paper will present preliminary results concerning the evolution of g9/2 orbital with increasing number of neutrons in the vicinity of N=40 nuclei.
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