Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

In-beam γ-ray spectroscopy of 80 Zn
Y. Shiga,∗1,∗2 K. Yoneda,∗1 D. Steppenbeck,∗1,∗3 N. Aoi,∗4 H. Baba,∗1 P. Bednarczyk,∗5 P. Doornenbal,∗1Zs. Dombradi,∗6 Zs. Fulop,∗6 S. Go,∗1,∗3 T. Hashimoto,∗4 E. Ideguchi,∗1,∗3 K. Ieki,∗1,∗2 K. Kobayashi,∗1,∗2Y. Kondo,∗1,∗7 J. Lee,∗1 H. Liu,∗1 M. Matushita,∗1,∗2 R. Minakata,∗1,∗6 T. Motobayashi,∗1 D. Nisimura,∗1H. Otsu,∗1 H. Sakurai,∗1 D. Sohler,∗6 Y. Sun,∗8 A. Tamii,∗4 S. Takeuchi,∗1 R. Tanaka,∗1,∗7 Z. Tian,∗8Zs. Vajta,∗6 H. Wang,∗1,∗8 T. Yamamoto,∗4 X. Yang,∗1 Z. Yang,∗8 Y. Ye,∗8 R. Yokoyama,∗1,∗3 and J. Zenihiro∗1In-beam γ-ray spectroscopy of nuclei in the vicinityof the doubly-magic nucleus 78 Ni was performed. In
recent studies, a drastic change of the shell structure
was elucidated for the neutron magic number N = 8,20, and 28 in the regions far from stability The energy of the ﬁrst I π = 2+ state E(2+1 ), and the energy+++ratio of the 4+
1 state to the 21 state E(41 )/E(21 ) ineven-even nuclei are of particular interest, since they
are sensitive to the evolution of the shell structure andnuclear deformation. In this study, the systematic energy trend of the low-lying states was investigated forthe chain of Zn isotopes 74,76,78,80, Zn which covers themagic number N = 50.
In order to produce RI beams around 80 Zn, a 238 U
primary beam with energy of 345A MeV was madeto impinge on a 925-mg/cm2 -thick beryllium target.
The fragments produced were separated and identiﬁed with the BigRIPS1) by the Bρ-∆E-ToF method
on an event-by-event basis. Then, the RI beams impinged on a 1889-mg/cm2 -thick beryllium target toinduce secondary reactions. The de-excitation γ-rays
emitted from reaction residues were observed by theNaI(Tl) detector array DALI22) , which surrounded thesecondary target. The reaction residues were identiﬁedusing the ZeroDegree spectrometer. Figure 1 shows theparticle identiﬁcation plots for the incoming particles
obtained with the BigRIPS (left) and for the outgoingparticles obtained with the ZeroDegree spectrometer(right).
Figure 2 shows the Doppler-shift corrected γ-ray
energy spectrum obtained for the reaction channel
9Be(81 Ga,80 Zn) with a restriction of a γ-ray multiplicity Mγ , being equal to 1. In the spectrum, ﬁve peaks
were observed. The peak at 1492(1) keV3) is for the+known γ-ray transition corresponding to the 2+
1 → 0g.s.
decay, while the other four transitions are candidates
for new levels and are still under analysis for conﬁrmation. Further analysis is on-going to reconstruct thelevel scheme by γ-γ coincidence, and to identify thespins and parities of the states by the analysis of momentum distribution of the outgoing reaction residues.
∗1∗2∗3∗4∗5∗6∗7∗8Fig. 1. Particle identification by the BigRIPS (left) and theZeroDegree spectrometer (right). Plotted is the proton
number against the ratio of mass to charge A/Q.

Fig. 2. Doppler-corrected γ-ray energy spectrum for
9Be(81 Ga,80 Zn) reaction with Mγ =1 condition. The
dotted curves are the response function with GEANT4simulation. The solid curve corresponds to the fittingof five response functions with exponential backgroundtaken into account. The spectrum, expanded to around2500 keV, is also shown in the upper inlet.

References
1) T. Kubo et al.: Prog. Theor. Exp. Phys. 03C003 (2012).
2) S. Takeuchi et al.: RIKEN Accel. Prog. Rep. 41, 149(2008).
3) J. Van. de Walle et al.: Phys. Rev. Lett. 99, 142501(2007).

RIKEN Nishina Center
Department of Physics, Rikkyo University
Center for Nuclear Study, University of Tokyo
RCNP, Osaka University
IFJ Pan
MTA Atomki
Department of Physics, Tokyo Institute of Technology
School of Physics, Peking University- 35 -