RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-1. Nuclear Physics

Spectroscopy of Single-Particle States in Oxygen Isotopes via
AO(p, 2p) Reaction with Polarized Protons
S. Kawase,∗1 T. L. Tang,∗1 T. Uesaka,∗2 D. Beaumel∗2,∗3 M. Dozono,∗2 T. Fujii,∗1,∗2 T. Fukunaga,∗2,∗4N. Fukuda,∗2 A. Galindo-Uribarri,∗5 S. H. Hwang,∗6 N. Inabe,∗2 D. Kameda,∗2 T. Kawahara,∗2,∗7 W. Kim,∗6K. Kisamori,∗1,∗2 M. Kobayashi,∗1 T. Kubo,∗2 Y. Kubota,∗1,∗2 K. Kusaka,∗2 C. S. Lee,∗1,∗2 Y. Maeda,∗8H. Matsubara,∗2 S. Michimasa,∗1 H. Miya,∗1∗2 T. Noro,∗2,∗4 A. Obertelli,∗9 S. Ota,∗1 E. Padilla-Rodal,∗10S. Sakaguchi,∗2,∗4 H. Sakai,∗2 M. Sasano,∗2 S. Shimoura,∗1 S. S. Stepanyan,∗6 H. Suzuki,∗2 M. Takaki,∗1,∗2H. Takeda,∗2 H. Tokieda,∗1 T. Wakasa,∗2,∗4 T. Wakui,∗2,∗11 K. Yako,∗1 Y. Yanagisawa,∗2 J. Yasuda,∗2,∗4R. Yokoyama,∗1,∗2 K. Yoshida,∗2 and J. Zenihiro∗2 for the SHARAQ04 collaboration
2222

count/5mm Excitation Energy of 21N (MeV)

9080706050403020100-200

7count/MeV!"O(p,2p)

80
70
60
50
40
30
20
100-10654O(p,2p)#$

30


-130
< xS1
< -60 
 (mm)

25
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20
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15

310

2
1

500-60< xS1< 10

 (mm)

25
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20
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-150

-100

-50

050

100

1500-20


200x S1 (mm)Fig. 1. Correlation between the excitation energy of 21 N
and xS1 .

We performed 14,22−24 O(p, 2p) reaction measurements (SHARAQ04 experiment) with a polarized proton target at RIBF to measure single-particle spectra and to determine spin-orbit splitting of 1p proton single-particle orbits in 14,22−24 O as a function of
their neutron number. For the experimental setup, seeref.1) . In this report, current status of the analysis for
22
O(p,2p) is described.
The (p, 2p) reaction was identiﬁed via the particle identiﬁcations of incident nuclei and two scatteredprotons. Particles were identiﬁed via the Time-ofFlight(TOF)-∆E method on an event-by-event basis.
Then the proton separation energy of the incident nuclei and the excitation energy of the residual nuclei
were calculated from scattering angles and TOF ofscattered protons.
Position of the residual nuclei and TOF from thetarget are also measured at a focal plane S1 at the∗1

Center for Nuclear Study (CNS), University of Tokyo
RIKEN Nishina Center∗3 Institut de Physique Nucléaire d’Orsay∗4 Department of Physics, Kyushu University∗5 Oak Ridge National Laboratory∗6 Department of Physics, Kyungpook National University∗7 Department of Physics, Toho University∗8 Department of Applied Physics, University of Miyazaki∗9 CEA Saclay∗10 Instituto de Ciencias Nucleares, Universidad Nacional
Autónoma de México∗11 CYRIC, Tohoku University
∗2-10
 0

10

20


30
 40
 50
 60
 70
 80
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
Excitationof 21N(MeV) Energy


Fig. 2. Excitation energy spectrum for 22 O(p, 2p) for eachxS1 region. The red lines show the background estimated from the 2p coincidence events occurred in thecarbon target.

downstream of the reaction point for the identiﬁcation of the residual particle in order to improve theS/N ratio and to separate the excited states of 21 N.
Figure 1 shows the correlation between the excitationenergy and the position of the residual nuclei at theS1 focal plane (xS1 ) after applying a TOF gate. At
S1, particles with larger Bρ come to the smaller xS1
region. There are two clear loci in the xS1 region of(−130, −60) and (−60, 10). The former corresponding
to 21 N and the latter should be 19 N or 20 N generated
through the neutron emission of 21 N. It will be clariﬁedby Bρ analysis.
Figure 2 shows the excitation energy spectra of 21 Nfor diﬀerent xS1 regions. The red lines show the background originated from the carbon contamination of
the polarized target and obtained from the measurement with a carbon target. At least two discrete states
are observed in these plots.
The cross sections, spectroscopic factors, and thespin-polarization observables such as the vector analyzing power are expected to be obtained through subsequent analyses in the near future.
References
1) S. Kawase et al.: RIKEN Accel. Prog. Rep., 46, 30(2013)- 56 -完全版2014_本文.indd 56

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