Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Intermediate-energy Coulomb excitation of 77 Cu
E. Sahin,∗1 V. Modamio,∗1 Z. Y. Xu,∗2 F. Bello,∗1 K. K. Hadyńska-Klȩk,∗1 P. Doornenbal,∗3 S. Chen,∗3,∗4
A. Jungclaus,∗5 R. Taniuchi,∗6 and the NP1406-RIBF126 collaboration
The present experimental study on 77 Cu has been
carried out at RI Beam factory (RIBF) of the RIKEN
Nishina Center1) . It will complement our previous
study of 77 Cu via beta decay of 77 Ni at RIKEN within
the EURICA campaign. The low-lying states in 77 Cu
were identified as particle-core excitations through thecomparison to the large scale Monte Carlo Shell Model(MCSM) calculations2,3) . An almost unique way tocharacterize the states predicted as collective in thecalculations is to measure the transition probabilities,i.e. B(E2) strengths. Hence the following Coulomb
excitation experiment was performed to study the collective properties of low-lying states in 77 Cu. The characterization of such states and in particular the mixingof both collective and single-particle configurations willprovide significant information on the shell structure
close to 78 Ni. A Coulomb excitation measurement of
the states due to the proton-core excitations in the caseof 77 Cu nucleus will also provide an estimation of thecollectivity of the 2+ state in th even-even 76 Ni ”core”.
Exotic secondary beam particles were produced byinduced fission of the 238 U beam on a 3-mm thick
9Be target. The uranium beam was accelerated toan energy of 345 MeV/nucleon with an average beam
intensity of 20 pnA. Fission products were selected
and transported by the BigRIPS fragment separator.
Coulomb excitation of the fragments was performed
on a 900-mg/cm2 thick 197 Au target, mounted in frontof the Zero Degree Spectrometer. The DALI2 NaI array was used to detect de-excitation γ ray measured incoincidence with beam-like particles identified in theZero Degree Spectrometer (ZDS). Two different beamsettings of the BigRIPS fragment separator have been
employed during the beam time. In the first one thecentral trajectory was set at 73 Cu as a test case toperform the absolute cross-section measurement technique (See Ref.4) for details). In the second setting,the momentum distribution of the incoming fragments
were centered for 77 Cu. Figures 1 and 2 show the preliminary particle identification (PID) spectra for ZDS,
i.e. after the Coulomb excitation target at F8 position. Note that 72 Ni was observed in the first setting
which will allow us to obtain the transition strength of+the 0+
1 to 21 transition and to fill the gap in the seniority parabola of the Ni chain from N=40 to N=46.
Data analysis in order to obtain doppler-corrected γ∗1∗2∗3∗4∗5∗6ray spectra for the extraction of the Coulomb excitation cross sections is still ongoing.

Fig. 1. Setting 1: 73 Cu and 72 Ni are identified in the Z(atomic number) versus A/Q (mass-to-charge number)plot for ZDS.

Fig. 2. Setting 2: 77 Cu and 78 Zn are identified in the Z(atomic number) versus A/Q (mass-to-charge number)plot for ZDS.

References
1) T. Onishi et al., J. Phys. Soc. Jpn. 79, 073201 (2010).
2) Y. Tsunoda, T. Otsuka, N. Shimizu, M. Honma, andY. Utsuno, Phys. Rev. C 89, 031301(R) (2014).
3) Y. Tsunoda et al., private communication.
4) P. Doornenbal et al., Phys. Rev. C 90, 061302(R)(2014).

University of Oslo, Department of Physics
University of Hong Kong
RIKEN Nishina CenterPeking University
Instituto de Estructura de la Materia, CSIC
University of Tokyo- 36 -