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von Neumann-Cosel P, Bassauer S, Martin D, Tamii A. Gamma Strength Functions and Level Densities from High-Resolution Proton Scattering under 0°. EPJ WEB OF CONFERENCES 2018. [DOI: 10.1051/epjconf/201817806002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Inelastic proton scattering at energies of a few 100 MeV and forward angles including 0° provides a novel method to measure gamma strength functions (GSF) in nuclei in an energy range of about 5 – 20 MeV. The experiments provide not only the E1 but also the M1 part of the GSF. The latter is poorly known in heavy nuclei. Comparison with gamma decay data (e.g. from the Oslo method) allows to test the generalised Brink-Axel (BA) hypothesis in the energy region of the pygmy dipole resonance (PDR) crucial for the modelling of (n,γ) and (γ,n) reactions in astrophysical reaction networks. From the two test cases studied, 208Pb remains inconclusive in the energy region of the PDR because of large Porter-Thomas fluctuations due to the small level density (LD), while the BA hypothesis seems to hold in case of 96Mo. A fluctuation analysis of the high-resolution data also provides a direct measure of the LD in the energy region of the isovector giant dipole resonance (IVGDR) well above the neutron threshold, where hardly any experimental information is available. This permits an independent test of the decomposition of GSF and LD in Oslo-type experiments.
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Martin D, von Neumann-Cosel P, Tamii A, Aoi N, Bassauer S, Bertulani CA, Carter J, Donaldson L, Fujita H, Fujita Y, Hashimoto T, Hatanaka K, Ito T, Krugmann A, Liu B, Maeda Y, Miki K, Neveling R, Pietralla N, Poltoratska I, Ponomarev VY, Richter A, Shima T, Yamamoto T, Zweidinger M. Test of the Brink-Axel Hypothesis for the Pygmy Dipole Resonance. PHYSICAL REVIEW LETTERS 2017; 119:182503. [PMID: 29219585 DOI: 10.1103/physrevlett.119.182503] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2016] [Indexed: 06/07/2023]
Abstract
The gamma strength function and level density of 1^{-} states in ^{96}Mo have been extracted from a high-resolution study of the (p[over →], p[over →]^{'}) reaction at 295 MeV and extreme forward angles. By comparison with compound nucleus γ decay experiments, this allows a test of the generalized Brink-Axel hypothesis in the energy region of the pygmy dipole resonance. The Brink-Axel hypothesis is commonly assumed in astrophysical reaction network calculations and states that the gamma strength function in nuclei is independent of the structure of the initial and final state. The present results validate the Brink-Axel hypothesis for ^{96}Mo and provide independent confirmation of the methods used to separate gamma strength function and level density in γ decay experiments.
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Affiliation(s)
- D Martin
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - P von Neumann-Cosel
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - A Tamii
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - N Aoi
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - S Bassauer
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - C A Bertulani
- Department of Physics and Astronomy, Texas A&M University-Commerce, Commerce, Texas 75429, USA
| | - J Carter
- School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - L Donaldson
- School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa
| | - H Fujita
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - Y Fujita
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - T Hashimoto
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - K Hatanaka
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - T Ito
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - A Krugmann
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - B Liu
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - Y Maeda
- Faculty of Engineering, Miyazaki University, Miyazaki 889-2192, Japan
| | - K Miki
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - R Neveling
- iThemba LABS, Somerset West 7129, South Africa
| | - N Pietralla
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - I Poltoratska
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - V Yu Ponomarev
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - A Richter
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
| | - T Shima
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - T Yamamoto
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - M Zweidinger
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
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Tamii A, Poltoratska I, von Neumann-Cosel P, Fujita Y, Adachi T, Bertulani CA, Carter J, Dozono M, Fujita H, Fujita K, Hatanaka K, Ishikawa D, Itoh M, Kawabata T, Kalmykov Y, Krumbholz AM, Litvinova E, Matsubara H, Nakanishi K, Neveling R, Okamura H, Ong HJ, Ozel-Tashenov B, Ponomarev VY, Richter A, Rubio B, Sakaguchi H, Sakemi Y, Sasamoto Y, Shimbara Y, Shimizu Y, Smit FD, Suzuki T, Tameshige Y, Wambach J, Yamada R, Yosoi M, Zenihiro J. Complete electric dipole response and the neutron skin in 208Pb. PHYSICAL REVIEW LETTERS 2011; 107:062502. [PMID: 21902316 DOI: 10.1103/physrevlett.107.062502] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Indexed: 05/31/2023]
Abstract
A benchmark experiment on (208)Pb shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.021)(+0.025) fm in (208)Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.
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Affiliation(s)
- A Tamii
- Research Center for Nuclear Physics, Osaka University, Ibaraki, Japan
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Kalmykov Y, Ozen C, Langanke K, Martínez-Pinedo G, von Neumann-Cosel P, Richter A. Spin- and parity-resolved level densities from the fine structure of giant resonances. PHYSICAL REVIEW LETTERS 2007; 99:202502. [PMID: 18233137 DOI: 10.1103/physrevlett.99.202502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Indexed: 05/25/2023]
Abstract
Level densities of J pi=2+ and 2- states extracted from high-resolution studies of E2 and M2 giant resonances in 58Ni and 90Zr are used to test recent predictions of a possible parity dependence. The experimental results are compared to a combinatorial approach based on the Hartree-Fock-Bogoliubov model and to shell-model Monte Carlo calculations including both spin and parity projection. No parity dependence is observed experimentally, which is in agreement for 90Zr but in contrast with the model predictions for 58Ni.
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Affiliation(s)
- Y Kalmykov
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
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Paar N, Vretenar D, Khan E, Colò G. Exotic modes of excitation in atomic nuclei far from stability. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2007; 70:R02. [PMID: 34996293 DOI: 10.1088/0034-4885/70/5/r02] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Indexed: 06/14/2023]
Abstract
We review recent studies of the evolution of collective excitations in atomic nuclei far from the valley of β-stability. Collective degrees of freedom govern essential aspects of nuclear structure, and for several decades the study of collective modes such as rotations and vibrations has played a vital role in our understanding of complex properties of nuclei. The multipole response of unstable nuclei and the possible occurrence of new exotic modes of excitation in weakly bound nuclear systems, present a rapidly growing field of research, but only few experimental studies of these phenomena have been reported so far. Valuable data on the evolution of the low-energy dipole response in unstable neutron-rich nuclei have been gathered in recent experiments, but the available information is not sufficient to determine the nature of observed excitations. Even in stable nuclei various modes of giant collective oscillations had been predicted by theory years before they were observed, and for that reason it is very important to perform detailed theoretical studies of the evolution of collective modes of excitation in nuclei far from stability. We therefore discuss the modern theoretical tools that have been developed in recent years for the description of collective excitations in weakly bound nuclei. The review focuses on the applications of these models to studies of the evolution of low-energy dipole modes from stable nuclei to systems near the particle emission threshold, to analyses of various isoscalar modes, those for which data are already available, as well as those that could be observed in future experiments, to a description of charge-exchange modes and their evolution in neutron-rich nuclei, and to studies of the role of exotic low-energy modes in astrophysical processes.
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Affiliation(s)
- Nils Paar
- Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstrasse 9, Darmstadt D-64289, Germany
- Physics Department, Faculty of Science, University of Zagreb, Bijenička 32, Zagreb 10000, Croatia
| | - Dario Vretenar
- Physics Department, Faculty of Science, University of Zagreb, Bijenička 32, Zagreb 10000, Croatia
| | - Elias Khan
- Institut de Physique Nucléaire, IN2P3-CNRS/Université Paris-Sud, Orsay 91406, France
| | - Gianluca Colò
- Dipartimento di Fisica dell'Università degli Studi and INFN, Sezione di Milano, via Celoria 16, Milano 20133, Italy
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Byelikov A, Adachi T, Fujita H, Fujita K, Fujita Y, Hatanaka K, Heger A, Kalmykov Y, Kawase K, Langanke K, Martínez-Pinedo G, Nakanishi K, von Neumann-Cosel P, Neveling R, Richter A, Sakamoto N, Sakemi Y, Shevchenko A, Shimbara Y, Shimizu Y, Smit FD, Tameshige Y, Tamii A, Woosley SE, Yosoi M. Gamow-Teller strength in the exotic odd-odd nuclei 138La and 180Ta and its relevance for neutrino nucleosynthesis. PHYSICAL REVIEW LETTERS 2007; 98:082501. [PMID: 17359091 DOI: 10.1103/physrevlett.98.082501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2006] [Indexed: 05/14/2023]
Abstract
The Gamow-Teller strength distributions below the particle threshold in 138La and 180Ta, deduced from high-resolution measurements of the (3He,t) reaction at 0 degrees, allow us to evaluate the role of charged-current reactions for the production of these extremely rare nuclides in neutrino-nucleosynthesis models. The analysis suggests that essentially all 138La in the Universe can be made that way. Neutrino nucleosynthesis also contributes significantly to the abundance of 180Ta but the magnitude depends on the unknown branching ratio for population of the long-lived isomer.
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Affiliation(s)
- A Byelikov
- Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
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Comtet A, Leboeuf P, Majumdar SN. Level density of a bose gas and extreme value statistics. PHYSICAL REVIEW LETTERS 2007; 98:070404. [PMID: 17359002 DOI: 10.1103/physrevlett.98.070404] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2006] [Indexed: 05/14/2023]
Abstract
We establish a connection between the level density of a gas of noninteracting bosons and the theory of extreme value statistics. Depending on the exponent that characterizes the growth of the underlying single-particle spectrum, we show that at a given excitation energy the limiting distribution function for the number of excited particles follows the three universal distribution laws of extreme value statistics, namely, the Gumbel, Weibull, and Fréchet distributions. Implications of this result, as well as general properties of the level density at different energies, are discussed.
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Affiliation(s)
- A Comtet
- Laboratoire de Physique Théorique et Modèles Statistiques, CNRS, Université de Paris-Sud, UMR 8626, 91405 Orsay Cedex, France
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