Neutron effective single-particle energies above Ni78 : A hint from lifetime measurements in the N=51 isotones Se85 and Kr87

Autor: S. Leoni, R. Menegazzo, C. Fransen, A. Gottardo, V. Vandone, E. Fioretto, L. Corradi, A. Dewald, Kamila Sieja, E. Sahin, L. Sengele, G. Duchêne, A. M. Stefanini, A. Bracco, G. Montagnoli, D. Mengoni, K. Kolos, E. Ellinger, M. Hackstein, S. Lunardi, S. Franchoo, D. R. Napoli, D. Montanari, F. Recchia, J. J. Valiente-Dobón, A. I. Morales, S. Bottoni, S. M. Lenzi, A. Goasduff, D. Verney, G. de Angelis, F. Didierjean, C. Michelagnoli, L. Grocutt, F. C. L. Crespi, D. Bazzacco, J. F. Smith, J. Litzinger, Suzana Szilner, F. Scarlassara, Megumi Niikura, R. Lozeva, O. Möller, E. Farnea, T. Mijatović, V. Modamio, C. A. Ur, Sibel Zehra Aydin, F. Ibrahim
Rok vydání: 2017
Předmět:
Zdroj: Physical Review C. 96
ISSN: 2469-9993
2469-9985
DOI: 10.1103/physrevc.96.044320
Popis: Background: While the $N=50$ shell-gap evolution towards $^{78}\mathrm{Ni}$ is presently in the focus of nuclear structure research, experimental information on the neutron effective single-particle energy sequence above the $^{78}\mathrm{Ni}$ 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.Purpose: In this study we probe the evolution of the $\ensuremath{\nu}1{g}_{7/2}$ effective single-particle energy which is a key to understanding the possible evolution of the spin-orbit splitting due to the proton-neutron interaction in the $^{78}\mathrm{Ni}$ region. To achieve this goal, a method based on lifetime measurements is used for the first time. The obtained lifetimes of the $7/{2}_{1}^{+}$ states in $^{87}\mathrm{Kr}$ and $^{85}\mathrm{Se}$ are used to investigate the $\ensuremath{\nu}1{g}_{7/2}$ evolution.Method: Yrast and near-yrast states in the light $N=51$ isotones $^{85}\mathrm{Se}$ and $^{87}\mathrm{Kr}$ were populated via multinucleon transfer reactions, using a $^{82}\mathrm{Se}$ beam and a $^{238}\mathrm{U}$ target at the LNL tandem-ALPI facility. The prompt $\ensuremath{\gamma}$ rays were detected by the AGATA Demonstrator and particle identification was performed using the PRISMA spectrometer. Lifetime measurements were performed by using the Cologne plunger device for deep inelastic reactions and the Recoil Distance Doppler Shift technique.Results: We obtain ${\ensuremath{\tau}}_{(7/{2}_{1}^{+})}=0.{4}_{\ensuremath{-}0.4}^{+1.6}$ ps for $^{87}\mathrm{Kr}$. In the case of $^{85}\mathrm{Se}$ an upper limit of 3(2) ps is obtained for the ${\ensuremath{\tau}}_{7/{2}_{1}^{+}}$ value.Conclusion: For $^{87}\mathrm{Kr}$, the measured $(7/{2}_{1}^{+})$ lifetime is consistent with a core-coupled ${2}^{+}\ensuremath{\bigotimes}\ensuremath{\nu}2{d}_{5/2}$ configuration for this state. This result is consistent with that obtained by direct reaction, which validates our method. For $^{85}\mathrm{Se}$, the measured $7/{2}_{1}^{+}$ lifetime limit indicates a very small contribution of the $\ensuremath{\nu}1{g}_{7/2}$ configuration to the wave function of this state.
Databáze: OpenAIRE
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