RIKEN Accel. Prog. Rep. 47 (2014)

HIGHLIGHTS OF THE YEAR

Exploration of cluster structure on neutron rich nuclei 16 C
with SAMURAI magnetic spectrometer
H. Otsu,∗1 M. Kurata-Nishimuira,∗1 Y. Togano,∗3 Y. Shimizu,∗1 H. Sato,∗1 T. Isobe,∗1 H. Baba,∗1 M. Sasano,∗1S. Takeuchi,∗1 P. Doornenbal, ∗1 N. Fukuda,∗1 K. Kusaka,∗1 J. Ohnishi,∗1 K. Yoneda,∗1 T. Motobayashi,∗1J. Zenihiro,∗1 J. Lee,∗1 H. Liu,∗1 H. Sakurai,∗1 T. Kobayashi,∗2 K. Sekiguchi,∗2 N. Chiga,∗2 T. Sumikama ,∗2K. Muto,∗2 Y. Wada,∗2 Y. Kondo,∗3 R. Minakata,∗3 S. Ogoshi,∗3 T. Nakamura,∗3 Y. Satou,∗4 J. Hwang,∗4Y. Matsuda,∗5,∗14 T. Murakami,∗5 N. Nakatsuka,∗5 T. Kawabata,∗5 J. Gibelin,∗6 S. Leblond,∗6,∗1
N. Kobayashi,∗7 M. Niikura,∗7 M. Matsushita,∗8,∗1 E. Yu. Nikolskii,∗9,∗1 S. Sakaguchi,∗10 D. Beaumel,∗11,∗1
A. Navin,∗12 V. Lapoux,∗13 and M. Itoh∗14
The highly excited states in weakly bound unstable nuclei have been attracting considerable interest recently. In particular, an important question iswhether alpha-cluster degree of freedom emerges near
the threshold in unstable nuclei as in stable nuclei. For
stable nuclei, the Ikeda diagram predicts such threshold cluster states, and many experimental evidences
have been reported1) . However, this threshold-rule has
not been examined for unstable nuclei.
The present study is aimed at searching cluster
states in the neutron-rich nucleus 16 C through α inelastic scattering at incident energy of 200 MeV/nucleon.
Such a technique has been successfully applied on various stable isotopes2) .
SAMURAI

200 A MeV12CLIFDAneutrons

Liq. 4He
TargetE (arb.)

16C beam

NEBULA

DFromBigRIPS

SBT/SBV
STQ25 BDC1/2

FDC2HODF

1m

FDC3HODP

16C

formed by using the SAMURAI spectrometer4) . The
large momentum acceptance property enables us to detect A/Z=3 particle and A/Z=2 particle including α
simultaneously. The experimental setup is shown in
Fig.1. The setup is similar to that used for the SAMURAI Day–one experiments5) . The A/Z=2 particles
were detected using A/Z=2 arm consisting of FDC3and HODP. The A/Z=3 particles were detected using
FDC2 and HODF (A/Z=3 arm). The correlation between ∆E and detector ID of HOD gated by the αparticle in the A/Z=2 arm is shown in Fig.2, where
11,12
Be arising from the breakup of 16 C can be clearlyidentified.
From the measured four momenta of α particle andthe corresponding Be isotopes, the invariant mass of16 ∗C will be reconstructed. For such a purpose, multiple track reconstruction techniques on drift chambers
have been developed6) . The analyses of the data arein progress.
gated on A/Z=2 arm

Z=412Be

beam

Fig. 1. Experimental setup. Detectors on the SAMURAI
focal plane are arranged for α + residual particle detection.

Hodoscope ID ~ position

Fig. 2. Particle identification on SAMURAI focal plane.
Z = 4 particles are identified on A/Z=3 arm in coincidence with α particles, which are gated on the A/Z=2arm.

A secondary beam of 16 C at 200 MeV/u and an intensity of 2×105 Hz is impinged on a 7 mm thick cryogenic liquid 4 He target3) . The experiment was per-In summary, we first measured the α dissociationchannel on excited 16 C using the SAMURAI spectrometer. Our future scope will focus on sd shell neutronrich nuclei such as 26−30 Ne.

∗1RIKEN Nishina Center
Department of Physics, Tohoku University∗3 Department of Physics, Tokyo Institute of Technology∗4 Department of Physics, Seoul National University∗5 Department of Physics, Kyoto University∗6 LPC Caen
∗7 Department of Physics, The University of Tokyo∗8 CNS, The University of Tokyo∗9 National Research Centre ”Kurchatov Institute”∗10 Department of Physics, Kyushu University∗11 Institut de Physique Nucl’eaire d Orsay, IN2P3/CNRS∗12 GANIL, CEA/DSM-CNRS/IN2P3∗13 CEA, Saclay∗14 CYRIC, Tohoku University∗15 RCNP, Osaka University∗2References
1) M. Freer, Rep. Prog. Phys. 70 (2007) 2149.
2) T. Kawabata et. al., Phys. Lett B 646, 6(2007).
3) M. Kurata-Nishimura, et. al., RIKEN Accel. Prog. Rep.
46(2013)165.
4) T. Kobayashi, et. al., Nucl. Instr. and Meth. B317(2013)294.
5) Y. Kondo, et. al., RIKEN Accel. Prog. Rep. 46(2013)6.
6) M. Kurata-Nishimura, et. al., RIKEN Accel. Prog. Rep. 47,this volume.

- xx -