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Electric dipole polarizability of $^{58}$Ni
Authors:
I. Brandherm,
F. Bonaiti,
P. von Neumann-Cosel,
S. Bacca,
G. Colò,
G. R. Jansen,
Z. Z. Li,
H. Matsubara,
Y. F. Niu,
P. -G. Reinhard,
A. Richter,
X. Roca-Maza,
A. Tamii
Abstract:
The electric dipole strength distribution in $^{58}$Ni between 6 and 20 MeV has been determined from proton inelastic scattering experiments at very forward angles at RCNP, Osaka. The experimental data are rather well reproduced by quasiparticle random-phase approximation calculations including vibration coupling, despite a mild dependence on the adopted Skyrme interaction. They allow an estimate…
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The electric dipole strength distribution in $^{58}$Ni between 6 and 20 MeV has been determined from proton inelastic scattering experiments at very forward angles at RCNP, Osaka. The experimental data are rather well reproduced by quasiparticle random-phase approximation calculations including vibration coupling, despite a mild dependence on the adopted Skyrme interaction. They allow an estimate of the experimentally inaccessible high-energy contribution above 20 MeV, leading to an electric dipole polarizability $α_\mathrm{D}(^{58}{\rm Ni}) = 3.48(31)$ fm$^3$. This serves as a test case for recent extensions of coupled-cluster calculations with chiral effective field theory interactions to nuclei with two nucleons on top of a closed-shell system.
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Submitted 1 October, 2024;
originally announced October 2024.
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Electric and magnetic dipole strength in $^{58}$Ni from forward-angle inelastic proton scattering
Authors:
I. Brandherm,
P. von Neumann-Cosel,
R. Mancino,
G. Martínez-Pinedo,
H. Matsubara,
V. Yu. Ponomarev,
A. Richter,
M. Scheck,
A. Tamii
Abstract:
The aim of the present work is a state-by-state analysis of possible E1 and M1 transitions in $^{58}$Ni with a high-resolution (p,p') experiment at 295 MeV and very forward angles including 0° and a comparison to results from studies of the dipole strength with the $(γ,γ')$ and (e,e') reactions. The E1 and M1 cross sections of individual peaks in the spectra are deduced with a multipole decomposit…
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The aim of the present work is a state-by-state analysis of possible E1 and M1 transitions in $^{58}$Ni with a high-resolution (p,p') experiment at 295 MeV and very forward angles including 0° and a comparison to results from studies of the dipole strength with the $(γ,γ')$ and (e,e') reactions. The E1 and M1 cross sections of individual peaks in the spectra are deduced with a multipole decomposition analysis and converted to reduced E1 and spin-M1 transition strengths using the virtual photon and the unit cross-section method, respectively. Despite the high level density good agreement is obtained for the deduced excitation energies of J = 1 states in the three types of experiments indicating that the same states are excited. The B(E1) and B(M1) strengths from the $(γ,γ^\prime)$ experiments are systematically smaller than in the present work because of the lack of information on branching ratios to lower-lying excited states and the competition of particle emission. Fair agreement with the B(M1) strengths extracted from the (e,e') data is obtained after removal of E1 transitions uniquely assigned in the present work, which belong to a low-energy toroidal mode with unusual properties mimicking M1 excitations in electron scattering. The experimental M1 strength distribution is compared to large-scale shell-model calculations with the effective GXPF1A and KB3G interactions. They provide a good description of the isospin splitting and the running sum of the M1 strength. A quenching factor 0.74 for the spin-isospin part of the M1 operator is needed to attain quantitative agreement with the data.
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Submitted 26 April, 2024; v1 submitted 24 April, 2024;
originally announced April 2024.
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Candidate toroidal electric dipole mode in the spherical nucleus $^{58}$Ni
Authors:
P. von Neumann-Cosel,
V. O. Nesterenko,
I. Brandherm,
P. I. Vishnevskiy,
P. -G. Reinhard,
J. Kvasil,
H. Matsubara,
A. Repko,
A. Richter,
M. Scheck,
A. Tamii
Abstract:
Dipole toroidal modes appear in many fields of physics. In nuclei, such a mode was predicted more than 50 years ago, but clear experimental evidence was lacking so far. Using a combination of high-resolution inelastic scattering experiments with photons, electrons and protons, we identify for the first time candidates for toroidal dipole excitations in the nucleus $^{58}$Ni and demonstrate that tr…
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Dipole toroidal modes appear in many fields of physics. In nuclei, such a mode was predicted more than 50 years ago, but clear experimental evidence was lacking so far. Using a combination of high-resolution inelastic scattering experiments with photons, electrons and protons, we identify for the first time candidates for toroidal dipole excitations in the nucleus $^{58}$Ni and demonstrate that transverse electron scattering form factors represent a relevant experimental observable to prove their nature.
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Submitted 9 November, 2024; v1 submitted 7 October, 2023;
originally announced October 2023.
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Electric dipole polarizability of $^{40}$Ca
Authors:
R. W. Fearick,
P. von Neumann-Cosel,
S. Bacca,
J. Birkhan,
F. Bonaiti,
I. Brandherm,
G. Hagen,
H. Matsubara,
W. Nazarewicz,
N. Pietralla,
V. Yu. Ponomarev,
P. -G. Reinhard,
X. Roca-Maza,
A. Richter,
A. Schwenk,
J. Simonis,
A. Tamii
Abstract:
The electric dipole strength distribution in $^{40}$Ca between 5 and 25 MeV has been determined at RCNP, Osaka, from proton inelastic scattering experiments at very forward angles. Combined with total photoabsorption data at higher excitation energy, this enables an extraction of the electric dipole polarizability $α_\mathrm{D}$($^{40}$Ca) = 1.92(17) fm$^3$. Together with the measured $α_{\rm D}$…
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The electric dipole strength distribution in $^{40}$Ca between 5 and 25 MeV has been determined at RCNP, Osaka, from proton inelastic scattering experiments at very forward angles. Combined with total photoabsorption data at higher excitation energy, this enables an extraction of the electric dipole polarizability $α_\mathrm{D}$($^{40}$Ca) = 1.92(17) fm$^3$. Together with the measured $α_{\rm D}$ in $^{48}$Ca, it provides a stringent test of modern theoretical approaches, including coupled cluster calculations with chiral effective field theory interactions and state-of-the art energy density functionals. The emerging picture is that for this medium-mass region dipole polarizabilities are well described theoretically, with important constraints for the neutron skin in $^{48}$Ca and related equation of state quantities.
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Submitted 18 April, 2023; v1 submitted 15 February, 2023;
originally announced February 2023.
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PANDORA project: photo-nuclear reactions below $A=60$
Authors:
A. Tamii,
L. Pellegri,
P. -A. Söderström,
D. Allard,
S. Goriely,
T. Inakura,
E. Khan,
E. Kido,
M. Kimura,
E. Litvinova,
S. Nagataki,
P. von Neumann-Cosel,
N. Pietralla,
N. Shimizu,
N. Tsoneva,
Y. Utsuno,
S. Adachi,
P. Adsley,
A. Bahini,
D. Balabanski,
B. Baret,
J. A. C. Bekker,
S. D. Binda,
E. Boicu,
A. Bracco
, et al. (56 additional authors not shown)
Abstract:
Photo-nuclear reactions of light nuclei below a mass of $A=60$ are studied experimentally and theoretically by the PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project. Two experimental methods, virtual-photon excitation by proton scattering and real-photo absorption by a high-brilliance gamma-ray beam produced by laser Compton scattering, will be applie…
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Photo-nuclear reactions of light nuclei below a mass of $A=60$ are studied experimentally and theoretically by the PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project. Two experimental methods, virtual-photon excitation by proton scattering and real-photo absorption by a high-brilliance gamma-ray beam produced by laser Compton scattering, will be applied to measure the photo-absorption cross sections and the decay branching ratio of each decay channel as a function of the photon energy. Several nuclear models, e.g. anti-symmetrized molecular dynamics, mean-field type models, a large-scale shell model, and ab initio models, will be employed to predict the photo-nuclear reactions. The uncertainty in the model predictions will be evaluated from the discrepancies between the model predictions and the experimental data. The data and the predictions will be implemented in a general reaction calculation code TALYS . The results will be applied to the simulation of the photo-disintegration process of ultra-high-energy cosmic rays in inter-galactic propagation.
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Submitted 18 November, 2022; v1 submitted 7 November, 2022;
originally announced November 2022.