While the N=50 shell-gap evolution towards ⁷⁸Ni is presently in the focus of nuclear  structure research, experimental information on the neutron effective single particle energy (ESPE) sequence above the ⁷⁸Ni core remain scarce. Direct nucleon exchange reactions are indeed difficult with presently available post-accelerated radioactive ion beams (especially for high orbital momentum orbitals) in this exotic region. We have studied the evolution of the νg7/2 ESPE which is the key to understanding the possible evolution of the spin-orbit splitting due to the action of the proton-neutron interaction terms in the ⁷⁸Ni region by measuring the lifetime of excited states in order to distinguish between collective and single-particle states. The evolution of the ESPE of this orbital, characterized by a high orbital momentum l=4, should indeed be particularly sensitive to tensor effects.

In the continuity of an experiment performed in LNL-Legnaro [1], we performed an experiment at GANIL (Caen, France) with AGATA [2], VAMOS [3] and the Orsay plunger OUPS [4] in order to measure lifetime of Yrast excited states (in peculiar 7/2₁⁺ states) in several N=51 isotones populated by the reaction  ²³⁸U(⁹Be,f). We particularly focused our study on ⁸³Ge, the closest N=51 odd isotones to ⁷⁹Ni for which detailed spectroscopy studies are possible within our experimental conditions. We also performed complementary β-delayed ^γ spectroscopy of ⁸³Ge with BEDO [5] at the ALTO ISOL photo-fission facility in Orsay to investigate non-Yrast spectroscopy.

Results from both experiments as well as on-going work at IGISOL will be presented and discussed.

REFERENCES

[1] F. Didierjean et al., Phys. Rev. C 96, 044320 (2017)
[2] E. Clément et al., NIM A 855 pp. 1-12 (2017)
[3] H. Savajols et al., NIM B 204 pp. 146-153 (2003)
[4] J. Ljungvall et al., NIM A 679 pp. 61-66 (2012)
[5] A. Etile et al., PRC 91, 064317 (2015)

 

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