-
S Takeuchi,
M Matsushita,
N Aoi,
P Doornenbal,
K Li,
T Motobayashi,
H Scheit,
D Steppenbeck,
H Wang,
H Baba, [......],
M Petri,
T Sako,
H Sakurai, S Shimoura,
K Steiger,
K Takahashi,
M Takechi,
Y Togano,
R Winkler,
K Yoneda
[show abstract]
[hide abstract]
ABSTRACT: Excited states in ^{38,40,42}Si nuclei have been studied via in-beam γ-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of ^{40}S and ^{44}S provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled γ-γ coincidence measurements. A prominent γ line observed with an energy of 742(8) keV in ^{42}Si confirms the 2^{+} state reported in an earlier study. Among the γ lines observed in coincidence with the 2^{+}→0^{+} transition, the most probable candidate for the transition from the yrast 4^{+} state was identified, leading to a 4_{1}^{+} energy of 2173(14) keV. The energy ratio of 2.93(5) between the 2_{1}^{+} and 4_{1}^{+} states indicates well-developed deformation in ^{42}Si at N=28 and Z=14. Also for ^{38,40}Si energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for ^{42}Si, the results show a rapid deformation development of Si isotopes from N=24 to N=28.
Physical Review Letters 11/2012; 109(18):182501. · 7.37 Impact Factor
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S. Takeuchi,
M. Matsushita,
N. Aoi,
P. Doornenbal,
K. Li,
T. Motobayashi,
H. Scheit,
D. Steppenbeck,
H. Wang,
H. Baba, [......],
M. Petri,
T. Sako,
H. Sakurai, S. Shimoura,
K. Steiger,
K. Takahashi,
M. Takechi,
Y. Togano,
R. Winkler,
K. Yoneda
[show abstract]
[hide abstract]
ABSTRACT: Excited states in 38,40,42Si nuclei have been studied via in-beam gamma-ray
spectroscopy with multi-nucleon removal reactions. Intense radioactive beams of
40S and 44S provided at the new facility of the RIKEN Radioactive Isotope Beam
Factory enabled gamma-gamma coincidence measurements. A prominent gamma line
observed with an energy of 742(8) keV in 42Si confirms the 2+ state reported in
an earlier study. Among the gamma lines observed in coincidence with the 2+ ->
0+ transition, the most probable candidate for the transition from the yrast 4+
state was identified, leading to a 4+_1 energy of 2173(14) keV. The energy
ratio of 2.93(5) between the 2+_1 and 4+_1 states indicates well-developed
deformation in 42Si at N=28 and Z=14. Also for 38,40Si energy ratios with
values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for 42Si,
the results show a rapid deformation development of Si isotopes from N=24 to
N=28.
07/2012;
-
K Tshoo,
Y Satou,
H Bhang,
S Choi,
T Nakamura,
Y Kondo,
S Deguchi,
Y Kawada,
N Kobayashi,
Y Nakayama, [......],
T Honda,
M Matsushita,
T Kobayashi,
Y Miyashita,
T Sumikama,
K Yoshinaga, S Shimoura,
D Sohler,
T Zheng,
Z X Cao
[show abstract]
[hide abstract]
ABSTRACT: The unbound excited states of the neutron drip-line isotope ^{24}O have been investigated via the ^{24}O(p,p^{'})^{23}O+n reaction in inverse kinematics at a beam energy of 62 MeV/nucleon. The decay energy spectrum of ^{24}O^{*} was reconstructed from the momenta of ^{23}O and the neutron. The spin parity of the first excited state, observed at E_{x}=4.65±0.14 MeV, was determined to be J^{π}=2^{+} from the angular distribution of the cross section. Higher-lying states were also observed. The quadrupole transition parameter β_{2} of the 2_{1}^{+} state was deduced, for the first time, to be 0.15±0.04. The relatively high excitation energy and small β_{2} value are indicative of the N=16 shell closure in ^{24}O.
Physical Review Letters 07/2012; 109(2):022501. · 7.37 Impact Factor
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Y Togano,
Y Yamada,
N Iwasa,
K Yamada,
T Motobayashi,
N Aoi,
H Baba,
S Bishop,
X Cai,
P Doornenbal, [......],
S Ota,
Y Satou, S Shimoura,
R Shioda,
K N Tanaka,
S Takeuchi,
W Tian,
H Wang,
J Wang,
K Yoneda
[show abstract]
[hide abstract]
ABSTRACT: The reduced transition probability BðE2; 0 þ gs ! 2 þ 1 Þ for 28 S was obtained experimentally using Coulomb excitation at 53 MeV=nucleon. The resultant BðE2Þ value 181ð31Þ e 2 fm 4 is smaller than the expectation based on empirical BðE2Þ systematics. The double ratio jM n =M p j=ðN=ZÞ of the 0 þ gs ! 2 þ
Physical Review Letters 06/2012; 108:222501. · 7.37 Impact Factor
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K. Tshoo,
Y. Satou,
H. Bhang,
S. Choi,
T. Nakamura,
Y. Kondo,
S. Deguchi,
Y. Kawada,
N. Kobayashi,
Y. Nakayama, [......],
T. Honda,
M. Matsushita,
T. Kobayashi,
Y. Miyashita,
T. Sumikama,
K. Yoshinaga, S. Shimoura,
D. Sohler,
T. Zheng,
Z. X. Cao
[show abstract]
[hide abstract]
ABSTRACT: The unbound excited states of the neutron drip-line isotope 24O have been
investigated via the 24O(p,p')23O+n reaction in inverse kinematics at a beam
energy of 62 MeV/nucleon. The decay energy spectrum of 24O* was reconstructed
from the momenta of 23O and the neutron. The spin-parity of the first excited
state, observed at Ex = 4.65 +/- 0.14 MeV, was determined to be Jpi = 2+ from
the angular distribution of the cross section. Higher lying states were also
observed. The quadrupole transition parameter beta2 of the 2+ state was
deduced, for the first time, to be 0.15 +/- 0.04. The relatively high
excitation energy and small beta2 value are indicative of the N = 16 shell
closure in 24O.
05/2012;
-
M. Niikura,
E. Ideguchi,
N. Aoi,
H. Baba,
T. Fukuchi,
Y. Ichikawa,
H. Iwasaki,
T. Kubo,
M. Kurokawa,
M. Liu,
S. Michimasa,
T. Ohnishi,
T. K. Onishi,
S. Ota, S. Shimoura,
H. Suzuki,
D. Suzuki,
Y. Wakabayashi,
K. Yoshida,
Y. Zheng
[show abstract]
[hide abstract]
ABSTRACT: In-beam g \gamma -ray spectroscopy of high-spin states in 49-51Ti was performed via the fusion-evaporation reaction using a radioactive beam. By excitation function and g \gamma -g \gamma coincidence analysis, yrast high-spin levels up to I = (21/2-),(11+),(17/2-) in 49-51Ti were determined. The levels were compared with full-pf -shell model calculation. The level structure indicates the persistency of the N = 28 shell gap at yrast states in 49-51Ti .
European Physical Journal A 05/2012; 42(3):471-475. · 2.19 Impact Factor
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YuGang Ma,
DeQing Fang,
XiaoYan Sun,
Pei Zhou,
XiangZhou Cai,
JinGen Chen,
Wei Guo,
WenDong Tian,
HongWei Wang,
GuoQiang Zhang, [......],
H. Sakurai, S. Shimoura,
R. Shioda,
E. Takeshita,
S. Takeuchi,
K. Yamada,
Y. Yamada,
Y. Yasuda,
K. Yoneda,
T. Motobayashi
[show abstract]
[hide abstract]
ABSTRACT: Two-proton relative momentum distributions from the break-up channels 23Al→p+p+21Na and 22Mg→p+p+20Ne at an energy of 60–70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator
beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component
from single-step 2He for highly excited 23Al and 22Mg.
Keywordsdiproton emission–proton-rich nuclei 23Al and 22Mg
Science China: Physics, Mechanics and Astronomy 05/2012; 54:18-23. · 0.78 Impact Factor
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Y. Togano,
Y. Yamada,
N. Iwasa,
K. Yamada,
T. Motobayashi,
N. Aoi,
H. Baba,
S. Bishop,
X. Cai,
P. Doornenbal, [......],
S. Ota,
Y. Satou, S. Shimoura,
R. Shioda,
K. N. Tanaka,
S. Takeuchi,
W. Tian,
H. Wang,
J. Wang,
K. Yoneda
[show abstract]
[hide abstract]
ABSTRACT: The reduced transition probability B(E2;0 ->2+) for 28S was obtained
experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2)
value 181(31) e2fm4 is smaller than the expectation based on empirical B(E2)
systematics. The double ratio |M_n/M_p|/(N/Z) of the 0+ ->2+ transition in 28S
was determined to be 1.9(2) by evaluating the M_n value from the known B(E2)
value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity
relative to that of neutrons. These results indicate the emergence of the magic
number Z=16 in the |T_z|=2 nucleus 28S.
04/2012;
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T Uesaka,
S Michimasa,
S Ota,
A Saito,
K Nakanishi,
Y Sasamoto,
K Miki,
S Noji,
H Tokieda,
H Miya, [......],
D Kameda,
T Kubo,
M Sasano,
H Baba,
K Itahashi,
G P A Berg,
D Bazin,
P Roussel-Chomaz,
Y Shimbara,
M Nagashima
[show abstract]
[hide abstract]
ABSTRACT: The high-resolution SHARAQ spectrometer and the dedicated beam-line have been constructed at the RI beam factory. Cathode-readout drift chambers placed at the focal plane of SHARAQ and multi-wire drift chambers in the beam-line worked satisfactorily for heavy ion beams with Z = 1–7 at 200–250 MeV/nucleon. By introducing a dispersion matched operation of the beam-line, we have achieved a momentum resolution of Δp/p = 1/8100 for a primary beam of 14N beam with a momentum spread of ±0.1%.
Journal of Physics Conference Series 09/2011; 312(5):052028.
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K Miki,
H Sakai,
T Uesaka,
H Baba,
G P A Berg,
N Fukuda,
D Kameda,
T Kawabata,
S Kawase,
T Kubo, [......],
S Ota,
A Saito,
Y Sasamoto,
M Sasano, S Shimoura,
H Takeda,
H Tokieda,
K Yako,
Y Yanagisawa,
R G T Zegers
[show abstract]
[hide abstract]
ABSTRACT: The isovector spin monopole resonances (IVSMR) of the β+ type were observed via the 208Pb and 90Zr(t, 3He) reactions at 300 MeV/u. The experiment was performed at the RI Beam Factory (RIBF) at RIKEN by using the newly-constructed magnetic spectrometer SHARAQ. The double differential cross sections for the 208Pb and 90Zr(t, 3He) reactions were obtained at the excitation energy of 0 ≤ Ex ≤ 70 MeV and the scattering angles of 0° ≤ 9 ≤ 3°. The monopole component was obtained as a difference between the zero-degree and backward-angle spectra. The signatures for the IVSMR were discovered at excitation energies of 12 MeV and 20 MeV in 208Pb and 90Zr, respectively, and they show good correspondences to the theoretical predictions.
Journal of Physics Conference Series 09/2011; 312(9):092040.
-
Y Togano,
T Motobayashi,
N Aoi,
H Baba,
S Bishop,
X Cai,
P Doornenbal,
D Fang,
T Furukawa,
K Ieki, [......], S Shimoura,
R Shioda,
K N Tanaka,
S Takeuchi,
W Tian,
H Wang,
J Wang,
K Yamada,
Y Yamada,
K Yoneda
[show abstract]
[hide abstract]
ABSTRACT: Coulomb dissociation of the proton-rich nucleus 31Cl was studied experimentally using a 31Cl beam at 58 MeV/nucleon with a lead target. The relative energy spectrum of 30S+p system was obtained from the measured momentum vectors of the reaction products detected in coincidence by the invariant mass method. The first excited state in 31Cl was observed which is relevant to the resonant capture in the stellar 30S(p,γ)31Cl reaction. Discussion for another observed state is also given.
Journal of Physics Conference Series 09/2011; 312(4):042025.
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Y. Satou,
T. Nakamura,
Y. Kondo,
N. Matsui,
Y. Hashimoto,
T. Nakabayashi,
T. Okumura,
M. Shinohara,
N. Fukuda,
T. Sugimoto, [......],
M. Ishihara,
S. Kawai,
H.J. Ong,
T.K. Onishi, S. Shimoura,
M. Tamaki,
T. Kobayashi,
Y. Matsuda,
N. Endo,
M. Kitayama
[show abstract]
[hide abstract]
ABSTRACT: A Gamow–Teller (GT) transition from the drip-line nucleus 14Be to 14B was studied via the (p,n) reaction in inverse kinematics using a secondary 14Be beam at 69 MeV/nucleon. The invariant mass method is employed to reconstruct the energy spectrum. A peak is observed at an excitation energy of 1.27(2) MeV in 14B, together with bumps at 2.08 and 4.06(5) MeV. The observed forward peaking of the state at 1.27 MeV and a good description for the differential cross section, obtained with a DWBA calculation provide support for the 1+ assignment to this state. By extrapolating the cross section to zero momentum transfer the GT-transition strength is deduced. The value is found to compare well with that reported in a β-delayed neutron emission study.
Physics Letters B. 02/2011;
-
Y Togano,
T Gomi,
T Motobayashi,
Y Ando,
N Aoi,
H Baba,
K Demichi,
Z Elekes,
N Fukuda,
Zs Fülöp, [......],
M Serata, S Shimoura,
T Sugimoto,
E Takeshita,
S Takeuchi,
K Ue,
K Yamada,
Y Yanagisawa,
K Yoneda,
A Yoshida
[show abstract]
[hide abstract]
ABSTRACT: The stellar reaction 26 Si(p,γ) 27 P was studied in the Coulomb dissociation of 27 P. Two known resonance levels in 27 P were excited and a candidate for the third excited state was found in the 26 Si p relative energy spectrum. The E2 resonance strengths ωγ were obtained to be (6.5 ± 1.3) × 10 −11 , (6.0 ± 1.1) × 10 −10 , and (1.10 ± 0.27) × 10 −10 MeV. The total (E2 + M1) ωγ value for the first excited state was evaluated to be 1.9 +1.9 −1.1 × 10 −9 MeV with the help of the shell model. The error was estimated from the deviation of theoretical predictions with the same shell model from experimental strengths obtained in the present study for 27 P and earlier ones for the mirror nucleus 27 Mg. The astrophysical reaction rate for the 26 Si(p,γ) 27 P reaction was also calculated and compared with previous estimations.
Physical Review C 01/2011; 035808(84). · 3.31 Impact Factor
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Y. G. Ma,
D. Q. Fang,
P. Zhou,
X. Z. Cai,
J. G. Chen,
W. Guo,
X. Y. Sun,
W. D. Tian,
H. W. Wang,
G. Q. Zhang, [......],
H. Sakurai, S. Shimoura,
R. Shioda,
E. Takeshita,
S. Takeuchi,
K. Yamada,
Y. Yamada,
Y. Yasuda,
K. Yoneda,
T. Motobayashi
[show abstract]
[hide abstract]
ABSTRACT: We have measured two‐proton momentum and angular correlations for the 23Al excited states from the 23Al radioactive beam on a 12C target at an energy of 60∼70 A MeV at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The decay products, namely 21Na+p+p from 23Al are clean identified. The relative momentum and opening angle between two protons in the rest frame of three body decay channels demonstrate that there are some diproton emission components from 2He cluster for the excited 23Al.
AIP Conference Proceedings. 05/2010; 1235(1):377-383.
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T. Uesaka,
S. Michimasa,
S. Ota,
A. Saito,
K. Nakanishi,
Y. Sasamoto,
H. Miya,
H. Tokieda,
S. Kawase,
Y. Shimizu, [......],
T. Kubo,
M. Sasano,
H. Baba,
K. Itahashi,
T. Ichihara,
G. P. A. Berg,
P. Roussel‐Chomaz,
D. Bazin,
Y. Shimbara,
M. Nagashima
[show abstract]
[hide abstract]
ABSTRACT: The high‐resolution SHARAQ spectrometer and the dedicated high‐resolution beamline have been constructed at RI beam factory and commissioned in 2009. Lateral and angular dispersion matching conditions were achieved simultaneously for a primay beam with a momentum spread of 0.1% and an emittance of 3π mm⋅mrad (σ). An overview of the spectrometer and the beam‐line, preliminary results from the commissioning runs, and future experimental plan with the system are described.
AIP Conference Proceedings. 04/2010; 1224(1):573-581.
-
T Nakamura,
N Kobayashi,
Y Kondo,
Y Satou,
N Aoi,
H Baba,
S Deguchi,
N Fukuda,
J Gibelin,
N Inabe, [......],
M Takechi,
S Takeuchi,
K Tanaka,
K N Tanaka,
N Tanaka,
Y Togano,
Y Utsuno,
K Yoneda,
A Yoshida,
K Yoshida
[show abstract]
[hide abstract]
ABSTRACT: The cross sections for single-neutron removal from the very neutron-rich nucleus 31Ne on Pb and C targets have been measured at 230 MeV/nucleon using the RIBF facility at RIKEN. The deduced large Coulomb breakup cross section of 540(70) mb is indicative of a soft E1 excitation. Comparison with direct-breakup model calculations suggests that the valence neutron of 31Ne occupies a low-l orbital (most probably 2p(3/2)) with a small separation energy (S(n) approximately < 0.8 MeV), instead of being predominantly in the 1f(7/2) orbital as expected from the conventional shell ordering. These findings suggest that 31Ne is the heaviest halo system known.
Physical Review Letters 12/2009; 103(26):262501. · 7.37 Impact Factor
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P Doornenbal,
H Scheit,
N Aoi,
S Takeuchi,
K Li,
E Takeshita,
H Wang,
H Baba,
S Deguchi,
N Fukuda, [......],
H Takeda,
K N Tanaka,
K Tanaka,
Y Togano,
M Winkler,
Y Yanagisawa,
K Yoneda,
A Yoshida,
K Yoshida,
H Sakurai
[show abstract]
[hide abstract]
ABSTRACT: We report on the first spectroscopic study of the N=22 nucleus 32Ne at the newly completed RIKEN Radioactive Ion Beam Factory. A single gamma-ray line with an energy of 722(9) keV was observed in both inelastic scattering of a 226 MeV/u 32Ne beam on a carbon target and proton removal from 33Na at 245 MeV/u. This transition is assigned to the deexcitation of the first Jpi=2+ state in 32Ne to the 0+ ground state. Interpreted through comparison with state-of-the-art shell-model calculations, the low excitation energy demonstrates that the "island of inversion" extends to at least N=22 for the Ne isotopes.
Physical Review Letters 08/2009; 103(3):032501. · 7.37 Impact Factor
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S. Takeuchi,
N. Aoi,
T. Motobayashi,
S. Ota,
E. Takeshita,
H. Suzuki,
H. Baba,
T. Fukui,
Y. Hashimoto,
K. Ieki, [......],
H. Sakurai, S. Shimoura,
R. Sugou,
D. Suzuki,
M. K. Suzuki,
M. Takashina,
M. Tamaki,
K. Tanaka,
Y. Togano,
K. Yamada
[show abstract]
[hide abstract]
ABSTRACT: Proton inelastic scattering on the neutron-rich nucleus 32Mg has been studied at 46.5 MeV/nucleon in inverse kinematics. Populated states were identified by measuring de-excitation γ rays, in which five new states were found by γ-γ coincidence analyses. By analyzing the angular differential cross sections via coupled-channel calculations, their spins and parities were constrained and the amplitudes for each transition were extracted. The spin and parity of the 2321-keV state was assigned as 41+. The ratio between the energies of the 21+ and 41+ states indicates that 32Mg is a transitional nucleus rather than an axially deformed rigid rotor. The collectivities in the nucleus 32Mg with N=20 are discussed based on the results obtained in the present experiment.
Phys. Rev. C. 05/2009; 79(5).
-
T. Nakamura,
N. Fukuda,
N. Aoi,
N. Imai,
M. Ishihara,
H. Iwasaki,
T. Kobayashi,
T. Kubo,
A. Mengoni,
T. Motobayashi,
M. Notani,
H. Otsu,
H. Sakurai, S. Shimoura,
T. Teranishi,
Y. X. Watanabe,
K. Yoneda
[show abstract]
[hide abstract]
ABSTRACT: The neutron capture reaction on 14C leading to the 15C ground state, which plays an important role in various nucleosynthesis processes, has been studied using the Coulomb breakup of 15C on a Pb target at 68 MeV/nucleon. The breakup cross section has been converted into the energy-dependent neutron capture cross section using the principle of detailed balance. The energy spectrum shows typical p-wave neutron capture characteristics, which is explained by the fact that the ground state of 15C possesses a strong single-particle s-wave component and a moderate-sized neutron halo structure. The capture cross section for the 14C(n,γ)15C reaction derived from the present experiment has been found to be consistent with the most recent data, directly measured using a 14C target. This result assures the validity of the Coulomb breakup method in deriving the neutron capture cross section for neutron-rich nuclei.
Phys. Rev. C. 03/2009; 79(3).
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N Aoi,
E Takeshita,
H Suzuki,
S Takeuchi,
S Ota,
H Baba,
S Bishop,
T Fukui,
Y Hashimoto,
H J Ong, [......],
T K Ohnishi,
H Sakurai, S Shimoura,
R Sugo,
D Suzuki,
M K Suzuki,
M Tamaki,
K Tanaka,
Y Togano,
K Yamada
[show abstract]
[hide abstract]
ABSTRACT: The structure of neutron-rich isotopes 60Cr and 62Cr was studied via proton inelastic scattering in inverse kinematics. The deformation lengths (delta) for 60Cr and 62Cr were extracted as 1.12(16) and 1.36(14) fm, respectively, providing evidence for enhanced collectivity in these nuclei. An excited state at 1180(10) keV in 62Cr was identified for the first time. We adopted 4;{+} as its spin and parity, leading to the rapid increase of the Ex(4;{+})/E_{x}(2;{+}) ratio, which indicates the development of large deformation in 62Cr near N=40. Importance of the admixture of the gd-shell component above N=40 is also discussed by comparing with a modern shell model calculation.
Physical Review Letters 02/2009; 102(1):012502. · 7.37 Impact Factor
