-
D. Kameda,
T. Kubo,
T. Ohnishi,
K. Kusaka,
A. Yoshida, K. Yoshida,
M. Ohtake,
N. Fukuda,
H. Takeda,
K. Tanaka, [......],
A. Ozawa,
T. Ohtsubo,
M. A. Famiano,
H. Geissel,
A. S. Nettleton,
O. B. Tarasov,
D. Bazin,
B. M. Sherrill,
S. L. Manikonda,
J. A. Nolen
[show abstract]
[hide abstract]
ABSTRACT: A search for isomeric gamma-decays among fission fragments from 345
MeV/nucleon 238U has been performed at the RIKEN Nishina Center RI Beam
Factory. Fission fragments were selected and identified using the
superconducting in-flight separator BigRIPS and were implanted in an aluminum
stopper. Delayed gamma-rays were detected using three clover-type high-purity
germanium detectors located at the focal plane within a time window of 20
microseconds following the implantation. We identified a total of 54
microsecond isomers with half-lives of ~0.1 - 10 microseconds, including
discovery of 18 new isomers in very neutron-rich nuclei: 59Tim, 90Asm, 92Sem,
93Sem, 94Brm, 95Brm, 96Brm, 97Rbm, 108Nbm, 109Mom, 117Rum, 119Rum, 120Rhm,
122Rhm, 121Pdm, 124Pdm, 124Agm and 126Agm, and obtained a wealth of
spectroscopic information such as half-lives, gamma-ray energies, gamma-ray
relative intensities and gamma-gamma coincidences over a wide range of
neutron-rich exotic nuclei. Proposed level schemes are presented for 59Tim,
82Gam, 92Brm, 94Brm, 95Brm, 97Rbm, 98Rbm, 108Nbm, 108Zrm, 109Mom, 117Rum,
119Rum, 120Rhm, 122Rhm, 121Pdm, 124Agm and 125Agm, based on the obtained
spectroscopic information and the systematics in neighboring nuclei. Nature of
the nuclear isomerism is discussed in relation to evolution of nuclear
structure.
11/2012;
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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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K. Kusaka,
M. Ohtake,
T. Ohnishi,
A. Yoshida, K. Yoshida,
T. Kubo,
Y. Yano,
M. Nobutoki,
H. Ito,
N. Kakutani,
T. Tsuchihashi,
K. Sato
[show abstract]
[hide abstract]
ABSTRACT: The BigRIPS fragment separator in the RIKEN RIBF project is characterized by fourteen superconducting triplet quadrupoles (STQ's) with large apertures and high-field gradients. While the five STQ's on the first stage of the BigRIPS are cooled by a liquid helium cryogenic plant, the nine STQ's on the second stage are cooled by small cryocoolers on their cryostat. This first stage serves to produce and separate RI beams, so that the first two STQs are exposed to the high radiation from the production target and beam dumps, which causes radiation heat loads as well as radiation damages. Measurements of the radiation heat loads to the cryostats of the first two STQs during commissioning operations of the RIBF facility are reported.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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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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J Gibelin,
D Beaumel,
T Motobayashi,
Y Blumenfeld,
N Aoi,
H Baba,
Z Elekes,
S Fortier,
N Frascaria,
N Fukuda, [......],
A Saito,
Y Satou,
J-A Scarpaci,
E Takeshita,
S Takeuchi,
T Teranishi,
Y Togano,
A M Vinodkumar,
Y Yanagisawa, K Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Coulomb excitation of the exotic neutron-rich nucleus (26)Ne on a (208)Pb target was measured at 58 MeV/u in order to search for low-lying E1 strength above the neutron emission threshold. This radioactive beam experiment was carried out at the RIKEN Accelerator Research Facility. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of B(E1)=0.49+/-0.16e(2) fm(2) is deduced, corresponding to 4.9+/-1.6% of the Thomas-Reiche-Kuhn sum rule. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is measured. The extracted decay pattern is not consistent with several mean-field theory descriptions of the pygmy states.
Physical Review Letters 12/2008; 101(21):212503. · 7.37 Impact Factor
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T. Kubo,
K. Kusaka, K. Yoshida,
A. Yoshida,
T. Ohnishi,
M. Ohtake,
Y. Yanagisawa,
N. Fukuda,
T. Haseyama,
Y. Yano,
N. Kakutani,
T. Tsuchihashi,
K. Sato
[show abstract]
[hide abstract]
ABSTRACT: Superconducting triplet quadrupoles (STQs) with large apertures and high field-gradients are employed for the in-flight radioactive-isotope (RI) beam separator BigRIPS at RIKEN. It consists of fourteen STQs and six room-temperature dipoles. The use of the STQs makes it possible to achieve important features of the BigRIPS separator: large acceptances and a large magnetic rigidity, allowing efficient production of RI beams. The BigRIPS separator is presently under construction and assembly as a major installation in the RIKEN RI-beam factory project, and the commissioning is scheduled in early 2007. In this paper we present the status and overview of the BigRIPS separator, emphasizing the STQs and their liquid-helium cryogenic systems.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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J Gibelin,
D. Beaumel,
T. Motobayashi,
N. Aoi,
H Baba,
Y. Blumenfeld,
Z. Elekes,
S. Fortier,
N. Frascaria,
N Fukuda, [......],
T Nakamura,
A Saito,
Y Satou,
E Takeshita,
S Takeuchi,
T Teranishi,
Y. Togano,
A. M. Vinodkumar,
Y Yanagisawa, K Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Coulomb excitation of the exotic neutron-rich nucleus $^{26}$Ne on a $^{nat}$Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an $^{nat}$Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV $^{40}$Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the $^{25}$Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed $^{26}$Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49$\pm$0.16 $e^2fm^2$ is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.
06/2007;
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J. Gibelin,
D. Beaumel,
T. Motobayashi,
N. Aoi,
H. Baba,
Y. Blumenfeld,
Zs. Dombrádi,
Z. Elekes,
S. Fortier,
N. Frascaria, [......],
T. Nakamura,
A. Saito,
Y. Satou,
E. Takeshita,
S. Takeuchi,
T. Teranishi,
Y. Togano,
A. M. Vinodkumar,
Y. Yanagisawa, K. Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Differential cross section of the inelastic scattering of a 54 MeV/nucleon 26Ne beam on a lead target has been measured by detecting the deexcitation γ-rays. Analysis of the first 2+ state angular distribution of the inelastically scattered nuclei shows that the process cannot be considered as a pure Coulomb excitation, and nuclear contribution must be taken into account. The charge deformation deduced, β2C=0.392±0.024, corresponds to a B(E2)=141±18 e2 fm2 in agreement with a N=16 subshell closure.
Phys. Rev. C. 05/2007; 75(5).
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D. Beaumel,
J. Gibelin,
T. Motobayashi,
N. Aoi,
H. Baba,
Y. Blumenfeld,
Z. Elekes,
S. Fortier,
N. Frascaria,
N. Fukuda, [......],
T. Nakamura,
A. Saito,
Y. Satou,
E. Takeshita,
S. Takeuchi,
T. Teranishi,
Y. Togano,
A. M. Vinodkumar,
Y. Yanagisawa, K. Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Coulomb excitation of the exotic neutron-rich nucleus 26Ne on a 208Pb
target was measured at 58 A.MeV in order to search for low-lying E1
strength above the neutron emission threshold. Data were also taken on
an Al target to estimate the nuclear contribution. The radioactive beam
was produced by fragmentation of a 95 A.MeV Ar beam delivered by the
RIKEN Research Facility. The set-up included a NaI gamma-ray array, a
charged fragment hodoscope and a neutron wall. Using the invariant mass
method in the 25Ne+n channel, we observe a sizable amount of E1 strength
between 6 and 10 MeV excitation energy. By performing a multipole
decomposition of the differential cross-section, a reduced dipole
transition probability of B(E1)=0.49+/-0.16 e2fm2 is deduced. For the
first time, the decay pattern of low-lying strength in a neutron-rich
nucleus is measured.
01/2007; 891:192-198.
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E. Ideguchi,
M. Niikura,
C. Ishida,
T. Fukuchi,
H. Baba,
N. Hokoiwa,
H. Iwasaki,
T. Koike,
T. Komatsubara,
T. Kubo, [......],
T. Ohnishi,
S. Ota,
A. Ozawa,
S. Shimoura,
T. Suda,
M. Tamaki,
I. Tanihata,
Y. Wakabayashi, K. Yoshida,
B. Cederwall
[show abstract]
[hide abstract]
ABSTRACT: A new method of in‐beam gamma‐ray spectroscopy induced by secondary fusion reactions, 37P+9Be and 46Ar+9Be is presented. Low‐energy secondary beams of 37P and 46Ar ions of ∼5 MeV/A were developed in order to induce fusion evaporation reactions. Excited states of nuclei in the vicinity of 48Ca, 49–52Ti and 46Ca, were studied by the method as well as β decay of the secondary beam 46Ar. Gamma‐gamma coincidence and excitation function analysis were performed to study high‐spin states of Ti isotopes. © 2005 American Institute of Physics
AIP Conference Proceedings. 04/2005; 764(1):136-141.
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[show abstract]
[hide abstract]
ABSTRACT: This is an attempt to explore feasibility to develop an open gradient magnetic separator for mixed powder under dry condition. The magnetic separator proposed here is intended to separate the ferromagnetic particles from mixed powder, being based on the consideration that the separation efficiency depends upon changing systematically the particle sizes and its surface properties such as hydrophobicity and cohesive force. As a result, it is found that the separation efficiency became lower as the particle size of the mixed particles became smaller. This is supposed to be caused by the cohesive force between the particles of ferrite and alumina which are easily affected by the magnetic drag force and the gravity difference. But the result is encouraging because the separation efficiency will be enhanced if the magnetic gradient is increased and if air flow in the separator is optimized in the appropriate system of the open-gradient magnetic separator proposed in this paper.
IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Three superferric quadrupoles with a pole-tip radius of 170 mm and a design field gradient of 14.1 T/m have been constructed and mapped for use as spectrometer elements. All three quadrupoles are assembled into a single cryostat and cooled by liquid-He bath cooling method. A small Gifford-McMahon/Joule-Thomson (GM/JT) cooler, mounted on the cryostat, requiries He gas that evaporates in the He vessel. The high-T<sub>c</sub> superconducting current leads and radiation shield surrounding the He-vessel, cooled by a small GM cooler, reduce the heat load of the He vessel. Both cryocoolers operate using separate water-cooled compressors and allow us a stand-alone operation of the quadrupole magnets without big cryoplant. Results of quench protection tests, measured heat loads and mapped results are presented.
IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor
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J. Gibelin,
D. Beaumel,
T. Motobayashi,
N. Aoi,
H. Baba,
Y. Blumenfeld,
Z. Elekes,
S. Fortier,
N. Frascaria,
N. Fukuda, [......],
T. Nakamura,
A. Saito,
Y. Satou,
E. Takeshita,
S. Takeuchi,
T. Teranishi,
Y. Togano,
A.M. Vinodkumar,
Y. Yanagisawa, K. Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Coulomb excitation of the exotic neutron-rich nucleus 26Ne on a natPb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an natAl target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV 40Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed 26Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49±0.16 e2fm2 is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.
Nuclear Physics A.
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T Uesaka,
S. Michimasa,
S Ota,
A Saito,
K Nakanishi,
Y Sasamoto,
H. Miya,
H. Tokieda,
S Kawase,
Y Shimizu, [......],
M Kurokawa,
M Sasano,
K. Itahashi,
H Baba,
T Ichihara,
Y. Shimbara,
M Nagashima,
G.P.A. Berg,
D. Bazin,
P. Roussel-Chomaz
RIKEN Accelerator Progress Report.
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Z. Elekes,
Zs. Dombrádi,
A. Krasznahorkay,
H. Baba,
M. Csatlós,
L. Csige,
N. Fukuda,
Zs. Fülöp,
Z. Gácsi,
J. Gulyás, [......],
T. Minemura,
T. Motobayashi,
A. Ozawa,
A. Saito,
S. Shimoura,
S. Takeuchi,
I. Tanihata,
P. Thirolf,
Y. Yanagisawa, K. Yoshida
[show abstract]
[hide abstract]
ABSTRACT: The neutron and proton excitations in 16C nucleus have been investigated by use of the Coulomb-nuclear interference method applied to the 208Pb+16C inelastic scattering. Angular distribution of the 16C nuclei in the inelastic channel populating the first 2+ state has been measured. The neutron and proton transition matrix elements, Mn and Mp, have been determined from the “Coulomb” and “matter” deformation-length parameters obtained by distorted wave calculations. The Mp or its corresponding B(E2;2+1→0+) value was found to be extremely small: 0.28±0.06 Weisskopf units consistent with a recent lifetime measurement. Furthermore, the extracted Mn/Mp ratio has an unexpectedly large value of 7.6±1.7. These results suggest that the 2+1 state in 16C is a nearly pure valence neutron excitation.
Physics Letters B.
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K. Yamada,
T. Motobayashi,
H. Akiyoshi,
N. Aoi,
Zs. Fülöp,
T. Gomi,
Y. Higurashi,
N. Imai,
N. Iwasa,
H. Iwasaki, [......],
T. Minemura,
S. Ozawa,
H. Sakurai,
M. Serata,
S. Shimoura,
S. Takeuchi,
T. Teranishi,
Y. Yanagisawa, K. Yoshida,
M. Ishihara
[show abstract]
[hide abstract]
ABSTRACT: The radiative width of the 3/2+ state at 6.793 MeV in 15O has been experimentally determined to be Γγ=0.95+0.60−0.95 eV by intermediate-energy Coulomb excitation. Our result independently supports the recent studies which point to a minor contribution of this state to the astrophysical rate of the 14N(p,γ)15O reaction in the CNO-cycle hydrogen burning in massive stars.
Physics Letters B.
-
T Ohnishi,
T Kubo,
K Kusaka,
A Yoshida, K Yoshida,
N Fukuda,
M Ohtake,
Y Yanagisawa,
H Takeda,
D. Kameda, [......],
Y Nakayama,
H. Geissel,
H. Weick,
J.A. Nolen,
O. B. Tarasov,
A.S. Nettleton,
D.P. Bazin,
B. M. Sherrill,
D. J. Morrissey,
W. Mittig
[show abstract]
[hide abstract]
ABSTRACT: A search for new isotopes using in-flight fission of a 345 MeV/nucleon $^{238}$U beam has been carried out in the commissioning experiment of the next-generation in-flight radioactive beam separator BigRIPS at the RI beam factory at the RIKEN Nishina Center. Two neutron-rich palladium isotopes $^{125}$Pd and $^{126}$Pd were observed for the first time, which demonstrates the great potential of the RIKEN RI beam factory.
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Zs. Dombrádi,
Z. Elekes,
R. Kanungo,
H. Baba,
Zs. Fülöp,
J. Gibelin,
Á. Horváth,
E. Ideguchi,
Y. Ichikawa,
N. Iwasa, [......],
S. Shimoura,
E. Takeshita,
S. Takeuchi,
I. Tanihata,
Y. Togano,
C. Wu,
Y. Yamaguchi,
Y. Yanagisawa,
A. Yoshida, K. Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Proton inelastic scattering study of 17B nucleus has been performed at 43.8 A MeV average energy in inverse kinematics using a liquid hydrogen target. In the Doppler corrected γ ray spectrum, a single peak with an energy of 1089(15) keV appeared corresponding to the first excited state of 17B. Based on the reaction cross section, deformation parameter of the transition is deduced by distorted wave analysis. Comparing it with the electric quadrupole moment of the nucleus, it is shown that the deformation of the neutron distribution is large (βn∼0.6), and the neutron effective charge is much smaller (en<0.12) than usual (∼0.5). The small effective charge is interpreted as a consequence of the decoupling of valence neutrons from the core.
Physics Letters B. 621:81-88.
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J Gibelin,
D. Beaumel,
T. Motobayashi,
N. Aoi,
H Baba,
Y. Blumenfeld,
Zs. Dombradi,
Z. Elekes,
S. Fortier,
N. Frascaria, [......],
T Nakamura,
A Saito,
Y Satou,
E Takeshita,
S Takeuchi,
T Teranishi,
Y. Togano,
A. M. Vinodkumar,
Y Yanagisawa, K Yoshida
[show abstract]
[hide abstract]
ABSTRACT: Differential cross section of the inelastic scattering of a 54 MeV/u 26Ne beam on a lead target has been measured by detecting the de-excitation $\gamma$-rays. Analysis of the first 2+ state angular distribution of the inelastically scattered nuclei shows that the process cannot be considered as a pure Coulomb excitation, and nuclear contribution must be taken into account. The charge deformation deduced, ¯C 2 = 0.392 ± 0.024, corresponds to a B(E2) = 141 ± 18 e2fm4 in agreement with a N = 16 sub-shell closure.
