Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Determination of neutron skin thickness via measurements ofσI and σCC of Ni isotopes
M. Takechi,∗1 M. Tanaka,∗2 A. Homma,∗1 Y. Tanaka,∗2 T. Suzuki,∗3 M. Fukuda,∗2 D. Nishimura,∗4T. Moriguchi,∗5 D. S. Ahn,∗6 A. S. Aimaganbetov,∗7,∗8 M. Amano,∗5 H. Arakawa,∗3 S. Bagchi,∗9 K.-H. Behr,∗9N. Burtebayev,∗7 K. Chikaato,∗1 H. Du,∗2 T. Fujii,∗3 N. Fukuda,∗6 H. Geissel,∗9 T. Hori,∗2 S. Hoshino,∗1R. Igosawa,∗3 A. Ikeda,∗1 N. Inabe,∗6 K. Inomata,∗3 K. Itahashi,∗6 T. Izumikawa,∗10 D. Kamioka,∗5N. Kanda,∗1 I. Kato,∗3 I. Kenzhina,∗11 Z. Korkulu,∗6 Ye. Kuk,∗7,∗8 K. Kusaka,∗6 K. Matsuta,∗2 M. Mihara,∗2E. Miyata,∗1 D. Nagae,∗6 S. Nakamura,∗1 M. Nassurlla,∗7 K. Nishimuro,∗3 K. Nishizuka,∗1 S. Ohmika,∗3K. Ohnishi,∗2 M. Ohtake,∗6 T. Ohtsubo,∗1 H. J. Ong,∗12 A. Ozawa,∗5 A. Prochazka,∗9 H. Sakurai,∗6C. Scheidenberger,∗9 Y. Shimizu,∗6 T. Sugihara,∗2 T. Sumikama,∗6 S. Suzuki,∗5 H. Suzuki,∗6 H. Takeda,∗6Y. K. Tanaka,∗9 T. K. Zholdybayev,∗7 T. Wada,∗1 K. Wakayama,∗3 S. Yagi,∗2 T. Yamaguchi,∗3R. Yanagihara,∗2 Y. Yanagisawa,∗6 and K. Yoshida∗3The exploration of the equation of state (EOS) of nuclear matter forms one of the most intriguing topics innuclear physics, wherein the investigation of the basic
properties of atomic nuclei plays a key role in the understanding of its parameters. Thus far, our abundant
knowledge of stable nuclei has suitably constrained theparameters of the EOS for symmetric nuclear matter1) .
However, the behavior of nuclear matter as a functionof the diﬀerence of neutron and proton numbers, whichis quite important to understand extremely asymmetric nuclear matter such as neutron stars and the coresof supernovae, is unfortunately more elusive. In orderto obtain a better understanding of the EOS of asymmetric matter, it is essential to study the symmetry
term of the EOS. Previous theoretical studies have indicated that the determination of neutron skin thickness ΔR as a function of the asymmetry parameterδ(≡ (N −Z)/A) yields crucial information to constrain
the symmetry energy coeﬃcient of the EOS2) . In thisregards, extensive studies have been carried out on stable nuclei thus far to determine ΔR3) , and a numberof data sets have been obtained in the range of δ from0 to 0.23; however, the data in the wider range of δ aredesirable to set a narrower constraint. In this study, wemeasured the interaction cross sections σI and chargechanging cross sections σCC for 58−78 Ni at the RIBF.
The matter radii of Ni isotopes can be deduced from σIwith the use of Glauber model4) and point-proton radii
can be deduced from σCC 5) ; consequently, the neutron
skin thickness of unstable nuclei can be obtained fromour measurements in this study.
The experiments were performed at the RIBF facil-
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ity operated by the RIKEN Nishina Center and theCenter for Nuclear study, University of Tokyo. A primary beam of 238 U (maximum intensity of around 30pnA) with incident beam energy of 345A MeV and Be
production targets were utilized to produce 58−78 Ni
secondary beams with energies around 260A MeV.
The σI values were measured by means of the transmission method6) and the BigRIPS fragment separator7) was used as a spectrometer to identify the incoming and outgoing particles of those nuclides thatremained unchanged from the original incident beam.
The schematic of the experimental setup is shown inFig. 1. The particle identiﬁcations for the analysisof cross sections are based on the ΔE − T OF − Bρmethod. In order to measure σCC , the large acceptance ion chamber was set at F5 to identify the particles that did not show change in the proton number
compared with that of the incident beam. Additional
reaction targets and MUlti Sampling Ion Chambers(MUSICs)8) were set at F11, which enabled us to deduce the σCC value of the beam transported throughzero-degree pectrometer (ZDS). Data analyses for σIand σCC are in progress.

 Fig. 1. Schematic of experimental setup.

References∗1

Department of Physics, Niigata University
Department of Physics, Osaka University∗3 Department of Physics, Saitama University∗4 Department of Physics, Tokyo University of Science∗5 Institute of Physics, University of Tsukuba∗6 RIKEN Nishina Center∗7 The Institute of Nuclear Physics Kazakhstan∗8 L. N. Gumilyov Eurasian National University∗9 GSI Helmholtzzentrum für Schwerionenforschung∗10 Radioactive Isotope Center, Niigata University∗11 Al-Farabi Kazakh National University∗12 Research Center for Nuclear Physics, Osaka University

1) J. Piekarewicz, Phys. Rev. C 76, 031301(R) (2007), andreferences therein.
2) M. Centelles et al. PRL 102, 122502 (2009).
3) L. Cao et al. Proceedings of the 14th National Conference on Nuclear Structure in China, p. 32.
4) I. Tanihata et al., Phys. Lett. B 287, 307 (1992).
5) T. Yamaguchi et al., PRL 107, 032502 (2011).
6) M. Takechi et al., Phys. Rev. C91, 014614(R) (2014).
7) T. Ohnishi et al., J. Phys. Soc. Jpn. 77, 083201 (2008).
8) A. Stolz et al., Phys. Rev. C 65, 064603 (2002).

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