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N Ryezayeva,
H Arenhövel,
O Burda,
A Byelikov,
M Chernykh,
J Enders,
H W Griesshammer,
Y Kalmykov,
P von Neumann-Cosel,
B Ozel,
I Poltoratska,
I Pysmenetska,
C Rangacharyulu,
S Rathi,
A Richter,
G Schrieder,
A Shevchenko,
O Yevetska
[show abstract]
[hide abstract]
ABSTRACT: Inclusive inelastic electron scattering off the deuteron under 180 degrees has been studied at the S-DALINAC close to the breakup threshold at momentum transfers q=0.27 fm;{-1} and 0.74 fm;{-1} with good energy resolution sufficient to map in detail the spin flip M1 response, which governs the starting reaction pn-->dgamma of big-bang nucleosynthesis over most of the relevant temperature region. Results from potential model calculations and (for q=0.27 fm;{-1}) from pionless nuclear effective field theory are in excellent agreement with the data.
Physical Review Letters 05/2008; 100(17):172501. · 7.37 Impact Factor
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N Ryezayeva,
H Arenhovel,
O Burda,
A Byelikov,
M Chernykh,
J Enders,
H W Grieshammer,
Y Kalmykov,
Özel B P Neumann-Cosel,
I Poltoratska,
I Pysmenetska,
C Rangacharyulu,
S Rathi,
A Richter,
G Schrieder,
A Shevchenko,
O Yevetska
[show abstract]
[hide abstract]
ABSTRACT: Inclusive inelastic electron scattering off the deuteron under 180° has been studied at the S-DALINAC close to the breakup threshold at momentum transfers q=0.27 fm-1 and 0.74 fm-1 with good energy resolution sufficient to map in detail the spin flip M1 response, which governs the starting reaction pn→dγ of big-bang nucleosynthesis over most of the relevant temperature region. Results from potential model calculations and (for q=0.27 fm-1) from pionless nuclear effective field theory are in excellent agreement with the data.
Physical Review Letters 01/2008; 100(17):172501 1-4. · 7.37 Impact Factor
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L Popescu,
C Baeumer,
A M Berg,
D Frekers,
D De Frenne,
Y Fujita,
E W Grewe,
P Haefner,
M N Harakeh,
M Hunyadi, [......],
H Johansson,
A Korff,
A Negret,
P Neumann-Cosel,
S Rakers,
A Richter, N Ryezayeva,
A Shevchenko,
H Simon,
H J Wortche
[show abstract]
[hide abstract]
ABSTRACT: The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios.
Physical Review C 05/2007; 75(5). · 3.31 Impact Factor
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A Negret,
T Adachi,
B R Barrett,
C Bäumer,
A M van den Berg,
G P A Berg,
P von Brentano,
D Frekers,
D De Frenne,
H Fujita, [......],
A Shevchenko,
Y Shimbara,
Y Shimizu,
Y Tameshige,
A Tamii,
M Uchida,
J Vary,
H J Wörtche,
M Yosoi,
L Zamick
[show abstract]
[hide abstract]
ABSTRACT: A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the beta decay of the A=14 multiplet is presented. The GT strength distributions to excited states in 14C and 14O were studied in high-resolution (d,2He) and (3He,t) charge-exchange reactions on 14N. No-core shell-model calculations capable of reproducing the suppression of the beta decays predict a selective excitation of Jpi=2+ states. The experimental confirmation represents a validation of the assumptions about the underlying structure of the 14N ground state wave function. However, the fragmentation of the GT strength over three 2+ final states remains a fundamental issue not explained by the present no-core shell model using a 6homega model space, suggesting possibly the need to include cluster structure in these light nuclei in a consistent way.
Physical Review Letters 09/2006; 97(6):062502. · 7.37 Impact Factor
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N Ryezayeva,
C Baeumer,
A M Berg,
L V Chulkov,
D Frekers,
D De Frenne,
E -W Grewe,
P Haefner,
E Jacobs,
H Johanson,
Y Kalmykov,
A Negret,
P Neumann-Cosel,
L Popescu,
S Rakers,
A Richter,
G Schrieder,
A Shevchenko,
H Simon,
H J Wortche
[show abstract]
[hide abstract]
ABSTRACT: A search for the J(pi) = 1/2(-) spin-orbit partner of the J(pi) = 3/2(-) ground state in He-7 has been performed with the Li-7(d, He-2) charge-exchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on Li-7 as well as on triton and He-4 clusters in the Li-7 ground state. A possible resonance at an excitation energy E-x approximate to 1.45 MeV with a width Gamma approximate to 2.0 MeV is suggested when the quasifree charge-exchange process on Li-7 is constrained by a measurement of the Li-6(d, He-2) reaction. Gamow-Teller strengths for transitions to the lowest states in He-7 deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations. (c) 2006 Elsevier B.V. All rights reserved.
Physics Letters B 01/2006; 639(6):623-628. · 3.95 Impact Factor
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A Negret,
T Adachi,
C Baumer,
AM Berg,
GPA Berg,
R Brentano,
D Frekers,
D De Frenne,
K Fujita,
Y Fujita, [......],
A Richter, N Ryezayeva,
Y Sakemi,
A Shevchenko,
Y Shimbara,
Y Shimizu,
A Tamii,
M Uchida,
HJ Wortche,
M Yosoi
[show abstract]
[hide abstract]
ABSTRACT: Two charge-exchange reactions were performed at intermediate energies in order to investigate the Gamow-Teller strength distribution starting from N-14(g.s). in beta(+) and beta(-) directions: N-14(d,He-2)C-14 and N-14(He-3,t) O-14. We describe here a few delicate details of the experimental techniques used in these investigations.
Capture Gamma-Ray Spectroscopy and Related Topics; 01/2006
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L Popescu,
T Adachi,
C Baeumer,
GPA Berg,
AM Berg,
P Brentano,
D Frekers,
D Frenne,
K Fujita,
Y Fujita, [......],
Y Sakemi,
A Shevchenko,
Y Shimbara,
Y Shimizu,
H Simon,
Y Tameshige,
A Tamii,
M Uchida,
HJ Wortche,
M Yosoi
[show abstract]
[hide abstract]
ABSTRACT: Spin-isospin (Gamow-Teller) excitations in Cu-64 and Co-64 have been studied using (He-3,t) and (d,He-2) charge-exchange reactions on Ni-64. As the isospin of the Ni-64 ground-state is T-0=4, states with T=3, 4 and 5 in Cu-64 are excited via the (He-3,t) reaction and states with T=5 in Co-64 via (d,He-2). If we assume that the nuclear interaction is charge symmetric, the T=5 states in Cu-64 should appear at corresponding excitation energies (if corrected for the Coulomb displacement) and with similar strengths as the T=5 states in Co-64. As in the Cu-64 spectrum the T=5 states are very weakly excited, only by combining the results of the two complementary experiments one can estimate the Gamow-Teller strength starting from Ni-64 in a consistent way.
Capture Gamma-Ray Spectroscopy and Related Topics; 01/2006
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N. Ryezayeva,
C. Bäumer,
A.M. van den Berg,
L.V. Chulkov,
D. Frekers,
D. De Frenne,
E.-W. Grewe,
P. Haefner,
E. Jacobs,
H. Johanson,
Y. Kalmykov,
A. Negret,
P. von Neumann-Cosel,
L. Popescu,
S. Rakers,
A. Richter,
G. Schrieder,
A. Shevchenko,
H. Simon,
H.J. Wörtche
[show abstract]
[hide abstract]
ABSTRACT: A search for the Jπ=1/2− spin–orbit partner of the Jπ=3/2− ground state in 7He has been performed with the charge-exchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on 7Li as well as on triton and 4He clusters in the 7Li ground state. A possible resonance at an excitation energy with a width is suggested when the quasifree charge-exchange process on 7Li is constrained by a measurement of the reaction. Gamow–Teller strengths for transitions to the lowest states in 7He deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations.
Physics Letters B. 01/2006; 639(6):623-628.
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P Neumann-Cosel,
C Baumer,
AM Berg,
D Frekers,
D De Frenne,
EW Grewe,
P Haefner,
E Jacobs,
H Johanson,
Y Kalmykov,
A Negret,
L Popescu,
S Rakers,
A Richter, N Ryezayeva,
G Schrieder,
A Shevchenko,
HJ Wortche
[show abstract]
[hide abstract]
ABSTRACT: A search for the J(pi) = 1/2(-) spin-orbit partner of the J(pi) = 3/2(-) ground state in He-7 has been performed with the Li-7(d, He-2) charge-exchange reaction. The results are incompatible with recent claims of such a state at very low excitation energy [Meister M et al 2002 Phys. Rev. Lett. 88 102501] but rather suggest a resonance with parameters E-x = (1.2(-0.4)(+0.5)) MeV, Gamma = (1.9(-0.4)(+0.8)) MeV. CT strengths deduced for the transitions to the lowest states in He-7 are in remarkable agreement with ab initio Quantum Monte Carlo calculations.
International Symposium on Correlation Dynamics in Nuclei; 01/2005
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L. Popescu,
D. de Frenne,
E. Jacobs,
A. Negret,
C. Baeumer,
D. Frekers,
E.W. Grewe,
P. Haefner,
A. Korff,
S. Rakers,
A.M. van den Berg,
M. Hunyadi,
M. de Huu,
H.J. Woertche,
Y. Fujita,
H. Johansson,
H. Simon,
P. von Neumann-Cosel, N. Ryezayeva,
A. Shevchenko
[show abstract]
[hide abstract]
ABSTRACT: The 64Ni(d,2He)64Co reaction was studied at the AGOR cyclotron of the KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a deuteron beam of 170 MeV. An energy resolution of about 100 keV was achieved. In addition to the ground-state with J{pi} = 1+, several other 1+ states could be identified and the strengths of the corresponding Gamow-Teller transitions determined.
AIP Conference Proceedings 09/2004; 726(1).
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A Negret,
T Adachi,
C Baumer,
AM Berg,
GPA Berg,
P Brentano,
D Frekers,
D De Frenne,
K Fujita,
Y Fujita, [......],
A Richter, N Ryezayeva,
Y Sakemi,
A Shevchenko,
Y Shimbara,
Y Shimizu,
A Tamii,
M Uchida,
HJ Wortche,
M Yosoi
[show abstract]
[hide abstract]
ABSTRACT: The Gamow-Teller (GT) strength distribution in the beta(-) and 01 directions starting from the ground state of N-14 has been investiated. A (d,He-2) experiment has been performed at KVI, Groningen with E-d=170 MeV and a (He-3,t) experiment at RCNP, Osaka with E-3He=420 MeV. It is found that, in both cases, the GT mechanism is populating mainly the 21 excited states in the final nuclei, while the ground state transitions are strongly suppressed. The analysis is ongoing.
NUCLEAR PHYSICS, LARGE AND SMALL; 01/2004
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L Popescu,
C Baumer,
AM Berg,
D Frekers,
D Frenne,
Y Fujita,
EW Grewe,
P Haefner,
M Hunyadi,
M Huu,
E Jacobs,
H Johansson,
A Korff,
A Negret,
P Neumann-Cosel,
S Rakers, N Ryezayeva,
A Shevchenko,
H Simon,
HJ Wortche
[show abstract]
[hide abstract]
ABSTRACT: The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of the KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a deuteron beam of 170 MeV. An energy resolution of about 100 keV was achieved. In addition to the ground-state with Jpi = 1(+), several other 1(+) states could be identified and the strengths of the corresponding Gamow-Teller transitions determined.
NUCLEAR PHYSICS, LARGE AND SMALL; 01/2004
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[show abstract]
[hide abstract]
ABSTRACT: A high-resolution (gamma,gamma') study of the electric dipole response in 208Pb at the S-DALINAC reveals a resonance structure centered around the neutron emission threshold. Microscopic quasiparticle phonon model calculations in realistic model spaces including the coupling to complex configurations are able to describe the data in great detail. The resonance is shown to result from surface density oscillations of the neutron skin relative to an approximately isospin-saturated core. It also forms an integral part of a toroidal E1 mode representing an example of vortex collective motion in nuclei.
Physical Review Letters 01/2003; 89(27):272502. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The neutron spectroscopic factor Sn of the 7He ground state is extracted from an R-matrix analysis of a recent measurement of the 7Li(d, 2He)7He reaction with good energy resolution. The width extracted from a deconvolution of the spectrum is Γ=183(22) keV (full width at half maximum, FWHM). The result Sn=0.64(9) is slightly larger than predictions of recent ‘ab initio’ Green's function Monte Carlo and fermionic molecular dynamics calculations.
Physics Letters B. 645:128-132.
