Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Intermediate energy Coulomb excitation of 73,74,75 Ni
A. Gottardo,∗1 G. de Angelis,∗1 P. Doornenbal,∗2 G. Benzoni,∗3 J. Lee,∗2 H. Liu,∗2 M. Matsushita,∗4D. Mengoni,∗5 V. Modamio-Hoybjor,∗1 S. Momiyama,∗6 T. Motobayashi,∗2 D. Napoli,∗1 M. Niikura,∗6E. Sahin,∗7 Y. Shiga,∗2,∗8 H. Sakurai,∗2,∗6 R. Taniuchi, ∗6 S. Takeuchi,∗2 H. Wang,∗2,∗12 J.J. Valiente-Dobòn,∗1
R. Avigo,∗3,∗11 H. Baba,∗2 N. Blasi,∗3 F.L. Bello Garrote,∗7 F. Browne,∗2,∗10 F.C.L. Crespi,∗3,∗11 S. Ceruti,∗3,∗11R. Daido,∗12 M.-C. Delattre,∗13 D. Fang,∗12 Zs. Dombradi,∗14 T. Isobe,∗2 I. Kuti,∗14 G. Lorusso,∗2 K. Matsui,∗6B. Melon,∗15 T. Miyazaki,∗6 S. Nishimura,∗2 R. Orlandi,∗16 Z. Patel,∗2,∗17 S. Rice,∗2,∗17 L. Sinclair,∗2,∗18
P.A. S¨oderstr¨om,∗2 D. Sohler,∗14 T. Sumikama,∗19 J. Taprogge,∗20,∗21 Zs. Vajta,∗14 H. Watanabe,∗2,∗22O. Wieland,∗3 J. Wu,∗2,∗19 Z. Y. Xu,∗6 M. Yalcinkaya,∗23 R. Yokoyama∗4Doubly magic nuclei located in very exotic regions of
the nuclear chart are key elements in nuclear structurestudies. The appearance or disappearance of the shellgaps associated with magic numbers in very exotic nuclei is strongly related to the single-particle energies ofnucleon orbitals and to the residual interactions among
valence nucleons. The 100 Sn and 78 Ni regions are fundamental in this regard and are the focus of the efforts of many research laboratories worldwide. From
the N=Z=50 100 Sn located at the proton drip line to
the neutron rich N=50 78 Ni with N/Z=1.78, it is currently possible to access the shell structure of theseisotones. This very large excursion in isospin also allows to magnify and probe the isovector part of thenuclear mean field. In particular, the tensor part ofthe spin-isospin term of the residual interaction has
been predicted to modify the single-particle structure,inducing a collective behavior in this region. For theNi isotopic chain, the filling up of the g9/2 neutron
orbit is expected to induce a strong core polarization
due to the spin-isospin interaction that enhances theB(E2:2+ → 0+ ), a measure of the quadrupole collectivity. We performed an intermediate energy Coulomb
excitation study of the 73,74,75 Ni isotopes, in order tofix the seniority-scheme pattern of the B(E2) strength.
Neutron-rich Ni isotopes were produced by fission of aCounts / 25 keV60+50

2+04030
2010600

800

1000 1200 1400
Energy (keV)

1600

1800Fig. 1. The γ-ray spectrum detected in DALI2 after selection on 74 Ni. The 2+ → 0+ transition at 1024 keV isclearly visible.

238

U beam on a 9 Be target at a bombarding energy of345 MeV/u, with an average intensity of 10 pnA. The
resulting fragments were analyzed using the BigRIPS
separator2) and transported to a secondary natural Pb
target for Coulex reactions. After this target, the ionswere again analyzed in the ZeroDegree spectrometerand delivered down to the final focal plane. The γ
rays from Coulex have been detected by the DALI2
spectrometer3) in coincidence with the recoiling ions
identified at the focal plane of the ZeroDegree spectrometer. A preliminary γ spectrum, after selection
on 74 Ni ions, is shown in Fig. 1. The γ peak corresponding to the 2+ → 0+ de-excitation at 1024 keVof 74 Ni4,5) is clearly visible. Decay spectroscopy investigation6) with EURICA was performed at the final
focal plane in conjunction with the in-beam part.

∗1LNL, INFNRIKEN, Nishina Center∗3 INFN sezione di Milano∗4 CNS, University of Tokyo∗5 Dipartimento di Fisica, Universitá degli Studi di Padova∗6 Department of Physics, University of Tokyo∗7 Department of Physics, University of Oslo
∗8 Department of Physics, Rikkyo University∗9 Department of Physics, Peking University∗10 School of Computing, Engineering and Mathematics,Brighton University∗11 Dipartimento di Fisica, Universitá degli Studi di Milano∗12 Departement of Physics, Osaka University∗13 IPN Orsay∗14 MTA Atomki∗15 INFN sezione di Firenze∗16 Instituut voor Kern- en Stralings Fysica/K.U.
∗17 Department of Physics, University of Surrey∗18 Department of Physics, University of York
∗19 Department of Physics, Tohoku University∗20 IEM, CSIC Madrid∗21 Department of Physics, Universidad Autònoma de Madrid∗22 Department of Physics, Beihang University∗23 Department of Physics, Istanbul University∗2References
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4) C. Mazzocchi et al.: Phys. Lett. B622, 45 (2005).
5) N. Aoi et al.: Phys. Lett. B692, 302 (2010).
6) G. Benzoni et al.: Riken annual report 2013.

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