Speaker
Description
F. Galtarossa$^1$, G. de Angelis$^2$, T. Marchi$^2$, L. Scomparin$^3$, T. Baumann$^4$, D. Bazin$^4$, A. Gade$^4$, A. Gottardo$^2$, P. R. John$^5$, M. Klintefjord$^6$, K. Kolos$^7$, S. M. Lenzi$^5$, D. Mengoni$^5$, C. Michelagnoli$^8$, V. Modamio$^6$, D. R. Napoli$^2$, S. Noji$^4$, J. Pereira$^4$, F. Recchia$^5$, E. Sahin$^6$, J. J. Valiente-Dobón$^2$, K. Wimmer$^9$, D. Weisshaar$^4$, R. Zegers$^4$, M. Dupuis$^{10}$, Y. Tsunoda$^{11}$ and T. Otsuka$^{12}$.
$^1$ INFN Sezione di Padova, Padova, Italy, $^2$ INFN Laboratori Nazionali di Legnaro, Padova, Italy $^3$ Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany $^4$ NSCL, Michigan State University - East Lansing (MI) 48824, USA, $^5$ Dipartimento di Fisica e Astronomia, Università di Padova, Italy, $^6$ Department of Physics, University of Oslo - Blindern, N-0316 Oslo, Norway, $^7$ Lawrence Livermore National Laboratory - Livermore, CA 94551, USA, 8 Institut Laue-Langevin (ILL) - 38042 Grenoble Cedex 9, France, $^9$ Instituto de Estructura de la Materia, CSIC - E-28006 Madrid, Spain, $^{10}$ CEA DIF, BP 12, 91680 Bruyères-le-Chatel, France, $^{11}$ Center for Nuclear Study, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan, $^{12}$ Department of Physics and Center for Nuclear Study, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
Transition matrix elements in exotic nuclei provide an important avenue for studying changes in shell structure, core polarization mechanisms, shape coexistence and other aspects of nuclear structure far from the valley of stability. In the nuclear chart the Nickel isotopic chain offers a unique opportunity to study the interplay between single-particle and collective excitations in atomic nuclei, for which important observables are the energy of the first 2+ excited state in even-even nuclei and the reduced transition probability B(E2; 2+→0+). The B(E2) can be indirectly measured via Coulomb Excitation (Coulex) and proton inelastic scattering. Coulex, being a purely electromagnetic probe under specific experimental conditions, is sensitive only to the proton contribution. Proton inelastic scattering, on the contrary, can assess the contribution of neutrons to the collectivity, and, more importantly, the ratio between the proton and neutron matrix elements.
In two experiments performed at the National Superconducting Cyclotron Laboratory (NSCL) of the Michigan State University (MSU) and at RIKEN (J) we measured the (p,p’) inelastic scattering and the Coulex of neutron-rich Ni isotopes 68,70,72Ni and 73,74,75Ni produced by induced fission at intermediate and relativistic energies. In the first case Radioactive Ni beams impinged at 80 MeV/u on a liquid hydrogen target and the scattered beam particles were detected in the S800 spectrometer while the coincident γ rays in the GRETINA γ-ray array. In the second experiment secondary Ni beams, after separation in the BIG RIPS spectrometer, were Coulomb excited before implantation in the position sensitive Si detector. Gamma rays were detected by the DALI2 scintillator array. In the first case the high γ-ray energy resolution of the GRETINA array allowed to identify yrast and yrare states in these nuclei and, from the measurement of the inelastic scattering cross section, to deduce their deformation length δ. Using the one-body density matrices from Monte Carlo Shell model, the combined results allowed to extract proton/neutron matrix elements for the different competing shapes. This experiment is complementary to a series of recent measurements in the region [1,2,3] and the results, which will be presented at the conference, help drawing a more complete picture on the nuclear structure evolution along the Z = 28 proton shell closure. Future programs using multinucleon transfer reactions at LNL with stable and radioactive secondary beams from the SPES facility will also be presented.
[1] N. Aoi, et al., Phys. Lett. B 692 (2010) 302.
[2] M. L. Cortés, et al., Phys. Rev. C 97, 044315 (2018).
[3] A. Gottardo et al., Phys. Rev. C 102, 014323 (2020).
