Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 48 (2015)

Quadrupole collectivity in island-of-inversion nuclei
28,30
Ne and 34,36 Mg†
S. Michimasa,∗1 Y. Yanagisawa,∗2 K. Inafuku,∗3 N. Aoi,∗4 Z. Elekes,∗5 Zs. Fülöp,∗5 Y. Ichikawa,∗2 N. Iwasa,∗3K. Kurita,∗6 M. Kurokawa,∗2 T. Machida,∗6 T. Motobayashi,∗2 T. Nakamura,∗7 T. Nakabayashi,∗7 M. Notani,∗8H. J. Ong,∗4 T. K. Onishi,∗9 H. Otsu,∗2 H. Sakurai,∗2,∗9 M. Shinohara,∗7 T. Sumikama,∗3 S. Takeuchi,∗2K. Tanaka,∗2 Y. Togano,∗7 K. Yamada,∗2 M. Yamaguchi,∗2 and K. Yoneda∗2We report here on the in-beam γ-ray spectroscopy
in very neutron-rich even-even nuclei of 28,30 Ne and34,36
Mg by proton inelastic scattering using a liquidhydrogen target in inverse kinematics. The 30 Ne nucleus has a conventional magic number of 20, and 36 Mg
is located in the middle of the shell closures of N = 20
and 28. The 30 Ne and 36 Mg are closer to the neutron
drip line than the nuclei belonging to the so-called “island of inversion (IOI)”. We have studied the evolution of quadrupole deformation on the side with moreneutrons and less protons than IOI. The report is acondensed version of our published paper1) .
The experiment was performed using the RIPS
beamline at the RI Beam Factory. A radioactive secondary beam, containing neutron-rich nuclei 32,34,36 Mg
and 28,30 Ne, was produced by fragmentation reactions
from 63-MeV/nucleon 48 Ca. Details of the experimental setup around the secondary target and beam conditions are provided in Ref.1) .
The angle-integrated cross sections for population of+
the 2+1 states were obtained from the yields of the 21 →+01 transitions with γ-detection multiplicity equal toone. The spectra are shown in Figs. 3–6, 8 in Ref.1) .
The deduced cross sections and deformation lengths
are summarized in Table 1.
The present results extended the measurements ofquadrupole collectivity along Ne and Mg isotopic

chains by providing deformation lengths with improved
accuracies for 28,30 Ne, 34 Mg and a new measurementfor 36 Mg. The systematic trends of the deformation
lengths are displayed in Fig. 1(a) and (b). The ﬁlled
and open circles indicate the deformation lengths deduced in the present work and those that have been estimated from the previous results using the WP09 potential2) , respectively. The thin black and thick orange
error bars represent statistical and systematic errors,respectively. The squares indicate previous results ofCoulomb excitation experiments.
Figures 1(a) and (b) also display several theoretical results that can be compared to the experimentalresults. The solid-blue and dashed-red lines are predictions by AMPGCM3) and the shell model with theSDPF-M eﬀective interaction4) , respectively. The shellmodel calculations in a 0h̄ω model space are shown by
the green dotted5) and orange dotted6) lines. For Mg
isotopes, the AMPGCM and SDPF-M calculations,which implement conﬁguration mixing around N = 20,
reproduce the systematic trend of experimental deformation lengths in a satisfactory manner. In addition,
they agree with the trend for the Ne isotopic chain, although they both systematically overestimate the experimental values.

Table 1. Angle-integrated cross sections for the 2+
1 statesand deduced deformation lengths in 28,30 Ne and32,34,36
Mg.
Nucleus28Ne30Ne32Mg
34Mg
36Mg
†∗1
∗2
∗3
∗4
∗5
∗6
∗7∗8∗9σ(2+1 ) (mb)
23(2)
37(4)
40+9−863(5)47(8)δ(p,p′ ) (fm)1.33 ± 0.06 (stat) ±0.05 (syst)
1.59+0.08−0.09 (stat) ±0.07 (syst)
1.85 ± 0.20 (stat) ±0.08 (syst)
2.30+0.09−0.10 (stat) ±0.16 (syst)
1.90+0.16−0.17 (stat) ±0.16 (syst)

Fig. 1. Systematics of deformation lengths around the IOIregion. Panels (a) and (b) show deformation lengths ofNe and Mg isotopes, respectively. Details are describedin the text.

Condensed from the article in Phys. Rev. C 89, 054307(2014).
Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
Department of Physics, Tohoku University
RCNP, Osaka University
ATOMKI
Department of Physics, Rikkyo University
Department of Physics, Tokyo Institute of Technology
Argonne National Laboratory
Department of Physics, University of Tokyo

References
1) S. Michimasa et al., Phys. Rev. C 89 (2014) 054307.
2) S.P. Weppner et al., Phys. Rev. C 80 (2009) 034608.
3) R.R. Rodrı́guez-Guzmán et al., Eur. Phys. J. A 17(2003) 37; Nucl. Phys. A 709 (2002) 201; Phys. Lett.
B 474 (2000) 15.
4) Y. Utsuno et al., Rhys. Rev. C 60 (1999) 054315.
5) E. Caurier et al., Rhys. Rev. C 58 (1998) 2033.
6) F. Nowacki and A. Poves, Phys. Rev. C 79 (2009)014310.

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