Background: While the N = 50 shell-gap evolution towards Ni-78 is presently in the focus of nuclear structure research, experimental information on the neutron effective single-particle energy sequence above the Ni-78 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 vlg(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 Ni-78 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 Kr-87 and Se-85 are used to investigate the vlg7/2 evolution. Method: Yrast and near-yrast states in the light N = 51 isotones Se-85 and Kr-87 were populated via multinucleon transfer reactions, using a Se-82 beam and a U-238 target at the LNL tandem-ALPI facility. The prompt y 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 (tau(7/21+)) = 0.4(-0.4)(+1.6) ps for Kr-87. In the case of Se-85 an upper limit of 3(2) ps is obtained for the (tau(7/21+)) value. Conclusion: For Kr-87, the measured (7/2(1)(+)) lifetime is consistent with a core-coupled 2(+) circle times v2d(5/2) configuration for this state. This result is consistent with that obtained by direct reaction, which validates our method. For Se-85, the measured (7/2(1)(+)) lifetime limit indicates a very small contribution of the vlg(7/2) configuration to the wave function of this state.

Neutron effective single-particle energies above Ni 78: A hint from lifetime measurements in the N=51 isotones Se 85 and Kr 87 / F. Didierjean, D. Verney, G. Duchêne, J. Litzinger, K. Sieja, A. Dewald, A. Goasduff, R. Lozeva, C. Fransen, G. De Angelis, S. Aydin, D. Bazzacco, A. Bracco, S. Bottoni, L. Corradi, F. Crespi, E. Ellinger, E. Farnea, E. Fioretto, S. Franchoo, A. Gottardo, L. Grocutt, M. Hackstein, F. Ibrahim, K. Kolos, S. Leoni, S. Lenzi, S. Lunardi, R. Menegazzo, D. Mengoni, C. Michelagnoli, T. Mijatovic, V. Modamio, O. Möller, G. Montagnoli, D. Montanari, A.I. Morales, D. Napoli, M. Niikura, F. Recchia, E. Sahin, F. Scarlassara, L. Sengele, S. Szilner, J.F. Smith, A.M. Stefanini, C. Ur, J.J. Valiente-Dobón, V. Vandone. - In: PHYSICAL REVIEW C. - ISSN 2469-9985. - 96:4(2017 Oct 20).

Neutron effective single-particle energies above Ni 78: A hint from lifetime measurements in the N=51 isotones Se 85 and Kr 87

S. Bottoni;F. Crespi;S. Leoni;V. Vandone
Ultimo
2017

Abstract

Background: While the N = 50 shell-gap evolution towards Ni-78 is presently in the focus of nuclear structure research, experimental information on the neutron effective single-particle energy sequence above the Ni-78 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 vlg(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 Ni-78 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 Kr-87 and Se-85 are used to investigate the vlg7/2 evolution. Method: Yrast and near-yrast states in the light N = 51 isotones Se-85 and Kr-87 were populated via multinucleon transfer reactions, using a Se-82 beam and a U-238 target at the LNL tandem-ALPI facility. The prompt y 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 (tau(7/21+)) = 0.4(-0.4)(+1.6) ps for Kr-87. In the case of Se-85 an upper limit of 3(2) ps is obtained for the (tau(7/21+)) value. Conclusion: For Kr-87, the measured (7/2(1)(+)) lifetime is consistent with a core-coupled 2(+) circle times v2d(5/2) configuration for this state. This result is consistent with that obtained by direct reaction, which validates our method. For Se-85, the measured (7/2(1)(+)) lifetime limit indicates a very small contribution of the vlg(7/2) configuration to the wave function of this state.
nuclear and high energy physics
Settore FIS/01 - Fisica Sperimentale
Settore FIS/04 - Fisica Nucleare e Subnucleare
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/557958
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