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Utsunomiya H, Goriely S, Renstrøm T, Tveten GM, Ari-izumi T, Miyamoto S, Lui YW, Larsen AC, Siem S, Hilaire S, Péru S, Koning AJ. γ-ray strength function for astrophysical applications in the IAEA-CRP. EPJ WEB OF CONFERENCES 2020. [DOI: 10.1051/epjconf/202023907005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The γ-ray strength function (γSF) is a nuclear quantity that governs photoabsorption in (γ, n) and photoemission in (n, γ) reactions. Within the framework of the γ-ray strength function method, we use (γ, n) cross sections as experimental constraints on the γSF from the Hartree-Fock-Bogolyubov plus quasiparticle-random phase approximation based on the Gogny D1M interaction for E1 and M1 components. The experimentally constrained γSF is further supplemented with the zero-limit M1 and E1 strengths to construct the downward γSF with which (n, γ) cross sections are calculated. We investigate (n, γ) cross sections in the context of astrophysical applications over the nickel and barium isotopic chains along the s-process path.
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Ngwetsheni C, Orce JN. How do we infer shell effects at high-excitation energies? A new spectroscopic probe to search for magic numbers. EPJ WEB OF CONFERENCES 2019. [DOI: 10.1051/epjconf/201922301045] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The nuclear dipole polarizability is mainly governed by the dynamics of the giant dipole resonance and, assuming validity of the brink-Axel hypothesis, has been investigated along with the effects of the low-energy enhancement of the photon strength function for nuclides in medium- and heavy-mass nuclei. Cubic-polynomial fitsto both data sets extrapolated down to a gamma-ray energy of 0.1 MeV show a significantreduction of the nuclear dipole polarizability for semi-magic nuclei, with magic numbers N =28, 50 and 82, which supports shell effects at high-excitation energies in the the quasi-continuum region. This work assigns σ-2 values as sensitive measures of long-range correlations of the nuclear force and provides a new spectroscopic probe to search for “old” and “new” magic numbers at high-excitation energies.
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Frauendorf S, Petrache CM, Schwengner R, Wimmer K. Decoherence of collective motion in warm nuclei. EPJ WEB OF CONFERENCES 2019. [DOI: 10.1051/epjconf/201922301017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Collective states in cold nuclei are represented by a wave function that assigns coherent phases to the participating nucleons. The degree of coherence decreases with excitation energy above the yrast line because of coupling to the increasingly dense background of quasiparticle excitations. The consequences of decoherence are discussed, starting with the well studied case of rotational damping. In addition to superdeformed bands, a highly excited oblate band is presented as a new example of screening from rotational damping. Suppression of pair correlation leads to incoherent thermal M1 radiation, which appears as an exponential spike (LEMAR) at zero energy in the γ strength function of spherical nuclei. In deformed nuclei a Scissors Resonance appears and LEMAR changes to damped magnetic rotation, which is interpreted as partial restoration of coherence.
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Sieja K. Electric and Magnetic Dipole Strength at Low Energy. PHYSICAL REVIEW LETTERS 2017; 119:052502. [PMID: 28949750 DOI: 10.1103/physrevlett.119.052502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Indexed: 06/07/2023]
Abstract
A low-energy enhancement of radiative strength functions was deduced from recent experiments in several mass regions of nuclei, which is believed to impact considerably the calculated neutron capture rates. In this Letter we investigate the behavior of the low-energy γ-ray strength of the ^{44}Sc isotope, for the first time taking into account both electric and magnetic dipole contributions obtained coherently in the same theoretical approach. The calculations are performed using the large-scale shell-model framework in a full 1ℏω sd-pf-gds model space. Our results corroborate previous theoretical findings for the low-energy enhancement of the M1 strength but show quite different behavior for the E1 strength.
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Affiliation(s)
- K Sieja
- Université de Strasbourg, IPHC, 23 rue du Loess 67037 Strasbourg, France and CNRS, UMR7178, 67037 Strasbourg, France
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Schwengner R, Frauendorf S, Brown BA. Low-Energy Magnetic Dipole Radiation in Open-Shell Nuclei. PHYSICAL REVIEW LETTERS 2017; 118:092502. [PMID: 28306274 DOI: 10.1103/physrevlett.118.092502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Indexed: 06/06/2023]
Abstract
Low-energy M1 strength functions of ^{60,64,68}Fe are determined on the basis of large-scale shell-model calculations with the goal to study their development from the bottom to the middle of the neutron shell. We find that the zero-energy spike, which characterizes nuclei near closed shells, develops toward the middle of the shell into a bimodal structure composed of a weaker zero-energy spike and a scissorslike resonance around 3 MeV, where the summed strengths of the two structures change within only 8% around a value of 9.8 μ_{N}^{2}. The summed strength of the scissors region exceeds the total γ absorption strength from the ground state by a factor of about three, which explains the discrepancy between total strengths of the scissors resonance derived from (γ, γ^{'}) experiments and from experiments using light-ion induced reactions.
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Affiliation(s)
- R Schwengner
- Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
| | - S Frauendorf
- Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - B A Brown
- National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
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Renstrøm T, Nyhus HT, Utsunomiya H, Larsen AC, Siem S, Guttormsen M, Filipescu DM, Gheorghe I, Goriely S, Bernstein LA, Bleuel DL, Glodariu T, Görgen A, Hagen TW, Lui YW, Negi D, Ruud IE, Şahin E, Schwengner R, Shima T, Takahisa K, Tesileanu O, Tornyi TG, Tveten GM, Wiedeking M. First evidence of low energy enhancement in Ge isotopes. EPJ WEB OF CONFERENCES 2015. [DOI: 10.1051/epjconf/20159304003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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10
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Kheswa BV, Wiedeking M, Giacoppo F, Goriely S, Guttormsen M, Larsen AC, Bello Garrote FL, Eriksen TK, Görgen A, Hagen TW, Koehler PE, Klintefjord M, Nyhus HT, Papka P, Renstrøm T, Rose S, Sahin E, Siem S, Tornyi T. Statistical nuclear properties and synthesis of 138La. EPJ WEB OF CONFERENCES 2015. [DOI: 10.1051/epjconf/20159304005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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13
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Brown BA, Larsen AC. Large low-energy M1 strength for ^{56,57}Fe within the nuclear shell model. PHYSICAL REVIEW LETTERS 2014; 113:252502. [PMID: 25554878 DOI: 10.1103/physrevlett.113.252502] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Indexed: 06/04/2023]
Abstract
A strong enhancement at low γ-ray energies has recently been discovered in the γ-ray strength function of ^{56,57}Fe. In this work, we have for the first time obtained theoretical γ decay spectra for states up to ≈8 MeV in excitation for ^{56,57}Fe. We find large B(M1) values for low γ-ray energies that provide an explanation for the experimental observations. The role of mixed E2 transitions for the low-energy enhancement is addressed theoretically for the first time, and it is found that they contribute a rather small fraction. Our calculations clearly show that the high-ℓ(=f) diagonal terms are most important for the strong low-energy M1 transitions. As such types of 0ℏω transitions are expected for all nuclei, our results indicate that a low-energy M1 enhancement should be present throughout the nuclear chart. This could have far-reaching consequences for our understanding of the M1 strength function at high excitation energies, with profound implications for astrophysical reaction rates.
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Affiliation(s)
- B Alex Brown
- National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321, USA
| | - A C Larsen
- Department of Physics, University of Oslo, N-0316 Oslo, Norway
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14
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Spyrou A, Liddick SN, Larsen AC, Guttormsen M, Cooper K, Dombos AC, Morrissey DJ, Naqvi F, Perdikakis G, Quinn SJ, Renstrøm T, Rodriguez JA, Simon A, Sumithrarachchi CS, Zegers RGT. Novel technique for constraining r-process (n, γ) reaction rates. PHYSICAL REVIEW LETTERS 2014; 113:232502. [PMID: 25526121 DOI: 10.1103/physrevlett.113.232502] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Indexed: 06/04/2023]
Abstract
A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the γ spectra from the β decay of ^{76}Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and γ-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ^{75}Ge(n,γ)^{76}Ge cross section and reaction rate.
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Affiliation(s)
- A Spyrou
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA
| | - S N Liddick
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
| | - A C Larsen
- Department of Physics, University of Oslo, NO-0316 Oslo, Norway
| | - M Guttormsen
- Department of Physics, University of Oslo, NO-0316 Oslo, Norway
| | - K Cooper
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
| | - A C Dombos
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA
| | - D J Morrissey
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
| | - F Naqvi
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
| | - G Perdikakis
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA and Central Michigan University, Mount Pleasant, Michigan, 48859, USA
| | - S J Quinn
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA and Department of Physics & Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
| | - T Renstrøm
- Department of Physics, University of Oslo, NO-0316 Oslo, Norway
| | - J A Rodriguez
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
| | - A Simon
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Department of Physics and The Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - C S Sumithrarachchi
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
| | - R G T Zegers
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA and Department of Physics & Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
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