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Title: Enhanced low-energy γ -decay strength of Ni 70 and its robustness within the shell model

Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their γ -emission probability at very low γ energies. In this work, we present measurements of the γ -decay strength of 70Ni over the wide range 1.3 < Eγ < 8 MeV. A significant enhancement is found in the γ -decay strength for transitions with Eγ < 3 MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed E1-strength calculations within the quasiparticle time-blocking approximation, which describe our data above Eγ > 5 MeV very well. Moreover, large-scale shell-model calculations indicate an M1 nature of the low-energy γ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation, and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich 72,74,76Ni.
Authors:
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Publication Date:
Grant/Contract Number:
NA0003221; ERC-STG-2014; 637686; 210007; 16-12-10155; AC52- 07NA27344; NA-0003180; NA-0000979; PHY 1102511; PHY 1430152; PHY 1350234; PHY 1404442; AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 97; Journal Issue: 5; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Research Org:
Michigan State Univ., East Lansing, MI (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); European Research Council (ERC); European Cooperation in Science and Technology (COST); Research Council of Norway (RCN); U.S.- Norway Fulbright Foundation for Educational Exchange; Russian Science Foundation; Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); National Science Foundation (NSF)
Contributing Orgs:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 79 ASTRONOMY AND ASTROPHYSICS; electromagnetic transitions; energy levels and level densities; nuclear astrophysics; nuclear structure and decays; nucleosynthesis in explosive environments; rare and new isotopes; shell model; 59 ≤ A ≤ 89
OSTI Identifier:
1465115
Alternate Identifier(s):
OSTI ID: 1439494; OSTI ID: 1465113