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(Li6, d) and (Li6, t) reactions on Ne22 and implications for s-process nucleosynthesis

S. Ota, G. Christian, W. N. Catford, G. Lotay, M. Pignatari, U. Battino, E. A. Bennett, S. Dede, D. T. Doherty, S. Hallam, F. Herwig, J. Hooker, C. Hunt, H. Jayatissa, A. Matta, M. Moukaddam, E. Rao, G. V. Rogachev, A. Saastamoinen, D. Scriven, J. A. Tostevin, S. Upadhyayula, and R. Wilkinson
Phys. Rev. C 104, 055806 – Published 24 November 2021
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  • INTRODUCTION
  • EXPERIMENTAL SETUP
  • Ne22 + Li6 EXPERIMENT
  • Ne22(Li6,d)Mg26 REACTION
  • ASTROPHYSICAL IMPLICATIONS
  • SUMMARY
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We studied α cluster states in Mg26 via the Ne22(Li6,dγ)Mg26 reaction in inverse kinematics at an energy of 7 MeV/nucleon. States between Ex = 4–14 MeV in Mg26 were populated and relative α spectroscopic factors were determined. Some of these states correspond to resonances in the Gamow window of the Ne22(α,n)Mg25 reaction, which is one of the main neutron sources in the astrophysical s-process. Using our new Ne22(α,n)Mg25 and Ne22(α,γ)Mg26 reaction rates, we performed new s-process calculations for massive stars and asymptotic giant branch stars and compared the resulting abundances with the abundances obtained using other Ne22+α rates from the literature. We observe an impact on the s-process abundances up to a factor of three for intermediate-mass AGB stars and up to a factor of ten for massive stars. Additionally, states in Mg25 at Ex < 7.5 MeV are identified via the Ne22(Li6,t)Mg25 reaction for the first time. We present the (Li6, t) spectroscopic factors of these states and note similarities to the (d,p) reaction in terms of reaction selectivity.

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    • Received 30 June 2021
    • Accepted 3 November 2021

    DOI:https://doi.org/10.1103/PhysRevC.104.055806

    ©2021 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Direct reactionsHydrostatic stellar nucleosynthesisNuclear reactionsNuclear spin & parityTransfer reactions
    1. Properties
    20 ≤ A ≤ 38
    Nuclear Physics

    Authors & Affiliations

    S. Ota1,2,*, G. Christian1,3,4,5, W. N. Catford6, G. Lotay6, M. Pignatari7,8,9,2, U. Battino10,2, E. A. Bennett1,4, S. Dede1,4, D. T. Doherty6, S. Hallam6, F. Herwig11,7,2, J. Hooker1,4, C. Hunt1,4, H. Jayatissa1,4, A. Matta6, M. Moukaddam6, E. Rao1,12, G. V. Rogachev1,4,5, A. Saastamoinen1, D. Scriven1,4, J. A. Tostevin6, S. Upadhyayula1,4, and R. Wilkinson6

    • 1Cyclotron Institute, Texas A&M University, College Station, Texas 77843, USA
    • 2NuGrid Collaboration, http://nugridstars.org
    • 3Department of Astronomy & Physics, Saint Mary's University, Halifax, NS B3H 3C3, Canada
    • 4Department of Physics & Astronomy, Texas A&M University, College Station, Texas 77843, USA
    • 5Nuclear Solutions Institute, Texas A&M University, College Station, Texas 77843, USA
    • 6Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom
    • 7Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, East Lansing, Michigan 48823, USA
    • 8E. A. Milne Centre for Astrophysics, Department of Physics and Mathematics, University of Hull, Hull HU6 7RX, United Kingdom
    • 9Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege M. t 15-17, 1121, Budapest, Hungary
    • 10School of Physics and Astronomy, University of Edinburgh, EH9 3FD, United Kingdom
    • 11Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2, Canada
    • 12Department of Physics & Astronomy, Rutgers University, New Brunswick, New Jersey, USA

    • *shuyaota@comp.tamu.edu

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    Issue

    Vol. 104, Iss. 5 — November 2021

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    Images

    • Figure 1
      Figure 1

      Total photopeak efficiency (sum of efficiency by each clover), together with data obtained using some conventional γ sources. Note the error bars are smaller than the symbol size.

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    • Figure 2
      Figure 2

      (a) Energy versus scattering angle plot from Ne22+CD2. Theoretical elastic (d,d) and (d,p) ground state kinematic lines are shown together. The elastic (p,p) line is because of contaminants in the target. (b) E−ΔE plot from a Barrel detector, where protons, deuterons, tritons, and He are observed.

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    • Figure 3
      Figure 3

      (a) Angular differential cross sections of Ne22(d,p) reactions for populating low-lying states of Ne23. (b) Excitation spectra of Ne23 from the Hyball at θc.m. = 5–12∘ (whole detector). Inset: Barrel at θc.m. = 18–19∘.

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    • Figure 4
      Figure 4

      Ex versus hit position on the focal plane in the Oxford detector. All excitation energies are constructed from Hyball-detected light particle momenta, assuming the Ne22(Li6,d) reaction. Right panel: gated on Mg26 recoil. Left panel: gated on Mg25 recoil. Clear correlations from the binary reactions (Li6,d) and (Li6,t) can be observed. In the Mg25 recoils, (Li6,d) kinematic lines are spread in x-direction due to neutron evaporation. Transition from Mg26 to Mg25 is clearly occurring at the neutron separation energy of Mg26 (11.09 MeV).

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    • Figure 5
      Figure 5

      Mg25 excitation energy spectrum measured from the Li6(Ne22,t)Mg25 reaction at θc.m. = 7∘–14∘.

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    • Figure 6
      Figure 6

      Angular differential cross sections of Ne22(Li6,t) reaction for populating various states of Mg25, compared with DWBA calculations. The excitation energies denoted on top of each panel are Mg25 excitation energies deduced from the spectra in Fig. 5. Jπ and energies in the legends are from Ref. [66].

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    • Figure 7
      Figure 7

      Mg26 excitation energy spectrum measured from the Li6(Ne22,d)Mg26 reaction at θc.m. = 7∘–14∘. All states considered in the present data analysis are labeled in the figure. These states are mostly determined with the help of the coincident γ rays and past (Li6,d) experiments. The energies shown are adopted by comparing our measured energies with Table 4.

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    • Figure 8
      Figure 8

      (a) γ-ray spectrum from Ne22(d,pγ)Ne23 reaction in coincidence with Ex = GS to 5 MeV from the proton excitation-energy spectrum. (b) γ-ray spectrum from the Ne22(Li6,dγ)Mg26 reaction in coincidence with Ex = 4–11.5 MeV. (c) γ-ray spectrum from the Ne22(Li6,dnγ)Mg25 reaction in coincidence with Ex (Mg26) = 11.0–14.0 MeV deuterons.

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    • Figure 9
      Figure 9

      Angular differential cross sections of Ne22(Li6,d) reactions for populating various states of Mg26, compared with DWBA calculations.

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    • Figure 10
      Figure 10

      Coincident (Li6,d) γ-ray spectra, gated on specific excitation energy ranges in Mg26. Note the last two panels (the blue-shaded histogram) were obtained by gating on Mg25 recoils instead of Mg26. The vertical dotted lines indicate the energies of major transitions from the low-lying states in Mg26: (a) 1003, (b) 1129, (c) 1808, and (d) 2510/2523 keV, respectively [see Fig. 8]. The vertical lines indicate 389, 585, 974, and 1611 keV transitions [major transitions from the low-lying states in Mg25; see Fig. 8] in the last two panels.

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    • Figure 11
      Figure 11

      Calculated s-process overproduction factors for the 3 and 5 M⊙ stars using various available Ne22(α,n) and Ne22(α,γ) rates. See text for details. Isotopes of the same elements are connected by adjoining lines [some key s-process peak isotopes (Sr88, Ba138, and Pb208) are labeled for clarification].

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    • Figure 12
      Figure 12

      Calculated s-process overproduction factors for the 25 M⊙ star using various available Ne22(α,n) and Ne22(α,γ) rates. See text for details. Isotopes of the same elements are connected by adjoining lines [some key s-process peak isotopes (Sr88, Ba138, and Pb208) are labeled for clarification].

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    • Figure 13
      Figure 13

      Calculated s-process overproduction factors using various available Ne22(α,n) and Ne22(α,γ) rates, for s-only nuclei. Top, middle, and bottom panels correspond to 3, 5, and 25 (in the middle of the C shell burning) M⊙ cases, respectively. Note that the rate given by Massimi et al. [38] is their upper limit (see texts for details).

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    • Figure 14
      Figure 14

      Ratios of calculated s-process abundances to TAMU abundances for the 3 and 5 M⊙ stars (see Fig. 11) using Ne22(α,n) and Ne22(α,γ) rates in which strength of some resonances are changed. See text for details. Isotopes of the same elements are connected by adjoining lines [some key s-process peak isotopes (Sr88, Ba138, and Pb208) are labeled for clarification].

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    • Figure 15
      Figure 15

      Ratios of calculated s-process abundances to TAMU abundances for the 25 M⊙ (see Fig. 12) using Ne22(α,n) and Ne22(α,γ) rates in which strength of some resonances are changed. See text for details. Isotopes of the same elements are connected by adjoining lines [some key s-process peak isotopes (Sr88, Ba138, and Pb208) are labeled for clarification].

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    • Figure 16
      Figure 16

      Calculated s-process abundance ratio to TAMU abundances for s-only nuclei (see Figs. 14 and 15) using Ne22(α,n) and Ne22(α,γ) rates in which strength of some resonances are changed. Top, middle, and bottom panels correspond to 3, 5, and 25 (in the middle of the C shell burning) M⊙ cases, respectively.

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