Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 48 (2015)

Measurement of unbound states in 17 C at SAMURAI
S. Kim,∗1,∗2 Y. Satou,∗1 J.W. Hwang,∗1,∗2 T. Nakamura,∗2,∗3 N. A. Orr,∗4 Y. Kondo,∗2,∗3 J. Gibelin,∗4N. Kobayashi,∗2,∗3 R. Tanaka,∗2,∗3 R. Minakata,∗2,∗3 S. Ogoshi,∗2,∗3 S. Nishi,∗2,∗3 D. Kanno,∗2,∗3T. Nakashima,∗2,∗3 N. L. Achouri,∗4 T. Aumann,∗5 H. Baba,∗2 F. Delaunay,∗4 P. Doornenbal,∗2 N. Fukuda,∗2N. Inabe,∗2 T. Isobe,∗2 D. Kameda,∗2 T. Kobayashi,∗6,∗2 T. Kubo,∗2 S. Leblond,∗4 J. Lee,∗2 F. M. Marqués,∗4T. Motobayashi,∗2 D. Murai,∗7 T. Murakami,∗8 K. Muto,∗6 N. Nakatsuka,∗8 A. Navin,∗9 H. Otsu,∗2 H. Sato,∗2Y. Shimizu,∗2 H. Suzuki,∗2 K. Takahashi,∗6 H. Takeda,∗2 S. Takeuchi,∗2 Y. Togano,∗10,∗13 A. G. Tuff,∗11M. Vandebrouck,∗12 and K. Yoneda∗2Department of Physics and Astronomy, Seoul National University∗2 RIKEN Nishina Center∗3 Department of Physics, Tokyo Institute of Technology∗4 LPC-Caen, ENSICAEN, Université de Caen, CNRS/IN2P3∗5 Institut für Kernphysik, Technische Universität Darmstadt∗6 Department of Physics, Tohoku University∗7 Department of Physics, Rikkyo University∗8 Department of Physics, Kyoto University∗9 GANIL, CEA/DSM-CNRS/IN2P3∗10 ExtreMe Matter Institute (EMMI) and Research Division,GSI∗11 Department of Physics, University of York∗12 Institut de Physique Nucléaire, Université Paris-Sud,
IN2P3-CNRS∗13 Department of Physics, Tokyo Institute of Technology∗12520dσ/dErel (mb/MeV)

To study unbound states in 17 C above the neutron
separation energy of 0.735(18) MeV1) , an experiment
was performed at RIBF during the first physics run of
the SAMURAI spectrometer2) . The unbound statesof 17 C were produced using the one-neutron knockout reaction of 18 C. The 18 C beam was provided byBigRIPS. The beam intensity was typically 2300 pps
with the energy of 250 MeV/nucleon under the momentum acceptance of ±3%. Particle identification of
the beam was carried out by employing the Bρ-TOF∆E method with a mass resolution of A/∆A = 770
at 1 sigma. The unbound states of 17 C populated by
one-neutron knockout of 18 C on a carbon reaction target with a thickness of 1.8 g/cm2 immediately decays
into a 16 C fragment and a neutron. The particle identification of this fragment was also carried out using
the Bρ-TOF-∆E method with a mass resolution ofA/∆A = 250 at 1 sigma. The identification of thestates of the 16 C fragment subsequent to the decay
was carried out on the basis of γ-n coincidence. The
de-excitation γ-rays in 16 C were detected by a γ-ray
detector array DALI23) , while neutrons were detectedby the neutorn detector array NEBULA consisting ofneutron detectors (NEUT) and charged-particle vetodetectors (VETO). For NEUT, the timing resolution
was 270 ps in a flight length of approximately 11 m.
The relative energy (Erel ) of 17 C was reconstructedusing the momentum vectors of the 16 C fragment andthe neutron. To determine the positions of the resonances, responses were generated using a Monte Carlosimulation that considers the beam characteristics, reaction mechanism, and detector resolutions. From thesimulation, the Erel resolution was evaluated as ∆Erel

15105001234

Erel (MeV)

567Fig. 1. Preliminary spectrum of the relative energy of 17 C.
The black solid line represents the result of the overall
fit by three responses (red solid lines) and a Maxwellian
background (a blue solid line).

√= 0.4 Erel MeV in FWHM.
A preliminary result of the fitting to the experimental spectrum with three responses and a Maxwellian
background is shown in Fig. 1 where resonances at
Erel = 0.58(3), 2.01(2), and 3.30(6) MeV are observed.
In this measurement, the resonance at E rel = 0.58(3)exhibited a correlation with a gamma line at 1.72(12)MeV, which corresponds to the 2+ state of 16 C4) .
Consequently, the three resonances correspond to excited states at 3.04(12), 2.75(3), and 4.04(6) MeV.
The excited states at 2.75(3) and 4.04(6) MeV are
likely to correspond to the states at 2.71(2) and 3.93(2)MeV, respectively, which have been observed in the βdelayed neutron measurement5) . Further analysis involving a comparison with Glauber model calculations
is in progress to investigate the orbital angular momentum and spin-parity of the observed resonances.
References
1) M. Wang, G. Audi, A. H. Wapstra, F. G. Kondev, M.
MacCormick, X. Xu, and B. Pfeiffer: Chin. Phys. C 36,1603 (2012).
2) T. Kobayashi et al.: Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
3) S. Takeuchi et al.: Nucl. Instrum. Methods Phys. Res.
A 763, 596 (2014).
4) D. R. Tilley et al.: Nucl. Phys. A 564, 1 (1993).
5) H. Ueno et al.: Phys. Rev. C 87, 034316 (2013).

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