RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

Search for unbound excited states of deformed halo nucleus 31 Ne
using breakup reactions
T. Tomai, ∗1,∗2 T. Nakamura, ∗1,∗2 Y. Togano, ∗1,∗2 Y. Kondo, ∗1,∗2 S. Takeuchi, ∗1,∗2 N. Kobayashi, ∗3A. Hirayama, ∗1,∗2 M. Matsumoto, ∗1,∗2 T. Ozaki, ∗1,∗2 A. T. Saito, ∗1,∗2 H. Yamada, ∗1,∗2 M. Yasuda, ∗1,∗2for SAMURAI27 collaboration
The neutron-rich odd nucleus 31 Ne, which is locatedin the “island of inversion,” has drawn much attention owing to its halo properties. Because this nucleus
has been found to have a p-wave 1n halo structure, it islikely to be strongly deformed.1) So far its deformation
properties have not been experimentally studied withdirect methods. No excited states in 31 Ne, which areexpected to be located in the unbound region because1)
of its small separation energy (Sn = 0.15+0.16−0.10 MeV),
have been studied. This experiment thus aims atstudying the excited states which should reﬂect therotational band caused by the deformation. In thepresent study, we applied the invariant mass methodto study the unbound states of 31 Ne in the inelastic
scattering reaction C(31 Ne, 30 Ne + n) and one neutron
removal reaction C(32 Ne, 30 Ne+n) to produce such excited states. In addition, we performed the Coulomb
breakup reaction Pb(31 Ne, 30 Ne + n) to obtain further
properties of the ground state.
In November 2016, we performed the SAMURAI27experiment. A 48 Ca primary beam with a high intensity of approximately 400 particle nA was directed toa Be target. Secondary beams of 31 Ne and 32 Ne were
produced and separated by BigRIPS. In this experiment, we used two diﬀerent settings of the BigRIPS
for 31 Ne and 32 Ne. The BigRIPS is settings are listed
shown in Table 1.
Particle identiﬁcation (PID) of the secondary beam
was performed by the ΔE-TOF-Bρ method. The energy loss ΔE was determined using an ionization chamber at F13 (ICB). The time of ﬂight TOF was measured using a 3-mm-thick plastic scintillator at F7 andtwo 0.5-mm-thick plastic scintillators at F13 (SBT).
The magnetic rigidity Bρ was calculated from the horizontal position of 3-mm-thick plastic scintillator at F5.
Figure 1 shows a resulting PID plot for the 31 Ne beam.
The intensity and the purity of the beams are summarized is shown in Table 1.
The secondary beam was transported to the SAMURAI experimental area and impinged on secondary targets at a bombarding energy of 230 MeV/nucleon. We
used a 2.15-g/cm2 -thick C target for the 31 Ne and 32 Ne
beams, and a 2.76-g/cm2 -thick Pb target for the 31 Nebeam. Charged particles and neutrons generated by
the breakup reactions were analyzed by the SAMURAI
spectrometer.2) The charged particles were detected by
the standard drift chambers of SAMURAI (FDC1 and∗1∗2∗3FDC2) and hodoscope (HODF24). Outgoing neutrons
were detected by NeuLAND3) and NEBULA, which
provide a high neutron eﬃciency of about 50%. Additionally, CATANA,4) a new γ-ray detector array, wasplaced around the secondary target. The data analysis
is in progress.
Table 1. BigRIPS settings for the 31 Ne and 31 Ne beams
and the resultant intensity and purity.
31Primary Be target (mm)F1 slit (mm)F1 Al wedge (mm)F5 slit (mm)
F5 Al wedge (mm)Total intensity (cps)Purity (%)

Ne
15±1208±1108∼ 1500
332Ne15±10010±508∼ 100
201310212Z

11103198
2.7

2.8

2.9

310Ne

3.1

3.2

3.3

A/ZFig. 1. PID plot for the 31 Ne beam setting. The horizontal
axis is mass-to-charge ratio A/Z and the vertical axis
is atomic number Z.

References
1) T. Nakamura et al., Phys. Rev. Lett. 112, 142501(2014).
2) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
3) http://www.fair-center.de/fileadmin/fair/experiments/
NUSTAR/Pdf/TDRs/NeuLAND-TDR-Web.pdf.
4) Y. Togano et al., RIKEN Accel. Prog. Rep. 48, 207(2015).

Department of Physics, Tokyo Institute of Technology
RIKEN Nishina Center
RCNP, Osaka University- 46 -