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Fission of Fr215 studied with γ spectroscopic methods

K. Miernik et al.
Phys. Rev. C 108, 054608 – Published 22 November 2023
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Article Text
  • INTRODUCTION
  • EXPERIMENTAL SETUP
  • GENERAL DESCRIPTION OF THE REACTION
  • ANALYSIS
  • DISCUSSION
  • SUMMARY
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    Background: Asymmetric fission is known to occur in two regions, the actinides and sublead, and is dependent on the fissioning system excitation energy. Experimental evidence in the sublead region show that this mode is surprisingly persistent with increasing energy and its origin is not fully understood.

    Purpose: To experimentally study the fusion-fission reaction of Fr215 at moderate excitation energy and determine previously unknown independent fission yields and other properties.

    Method: The compound nucleus was formed in the reaction O18+Au197. The prompt γ rays emitted during the reaction were measured with the high efficiency and high granularity ν-ball-2 spectrometer. Independent fission yields of even-even nuclei were determined by detecting triple-gamma cascades in the fission fragments.

    Results: The observed yields, although dominated by a symmetric peak, show maxima for heavy fragment of Z≈54–56, which is consistent with the known results in the actinide region but unexpected for the nuclide of interest, and at the studied excitation energy.

    Conclusions: The mode of asymmetric fission is present even at relatively high excitation energies in the system studied. This observation matches experimental findings in the sublead region, contrary to the actinides, and so far there is no well-developed explanation of this phenomenon.

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    • Received 24 July 2023
    • Accepted 2 November 2023

    DOI:https://doi.org/10.1103/PhysRevC.108.054608

    ©2023 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    FissionLow & intermediate energy heavy-ion reactionsNuclear fusionNuclear reactions
    1. Properties
    A ≥ 220
    1. Techniques
    Gamma ray spectroscopy
    Nuclear Physics

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    Issue

    Vol. 108, Iss. 5 — November 2023

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    Images

    • Figure 1
      Figure 1

      Reaction rates per s per 1 nA intensity of beam for main reaction channels as calculated by hivap [24] as a function of the experimental beam energy range (111–0 MeV). Arrows indicate effective excitation energy of CN for fission events (E★) and theoretical fusion barrier height (B) [30]. The orange curve shows the average value with the band representing one standard deviation of the total angular momentum of the CN as calculated by the pace4 code [27, 28]. The hatched area shows the position of the CN on the E*−J space within one standard deviation.

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    • Figure 2
      Figure 2

      The total γ ray spectrum from HPGe detectors obtained during the experiment. Some major γ lines are marked with their origin. See text for more details.

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    • Figure 3
      Figure 3

      Example of γ−γ spectrum (top), γ−γ spectrum with background subtraction (middle), and γ−γ−γ spectrum (bottom) gated on the known 270 keV (2+→0+) or 445 keV (4+→2+) transitions in the Ru106. Black dashed lines show position of the identified transitions, red dashed lines show the neutron scattering lines and the e+e− annihilation line. See text for more details.

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    • Figure 4
      Figure 4

      Example of the observed feeding patterns of fission fragments. Black numbers indicate levels and their spin. Blue values show gamma transitions and their relative intensity in brackets. Red labels and arrow show observed feeding to the indicated state.

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    • Figure 5
      Figure 5

      Individual fragments levels population in function of mass. Crosses show calculated average spin per fragment. Fragments of the same mass are sorted by their charge, and shown next to each other. See text for more details.

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    • Figure 6
      Figure 6

      Experimental and calculated fragment charge distributions (see text for more details).

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    • Figure 7
      Figure 7

      Left: experimental fragment yield, color encoded. Middle: fragment yield calculated by gef model [7] for experimental excitation energy and angular momentum. Right: fragment yield calculated by Mumpower et al. [11] for excitation energy 20 MeV and L=0. Dashed lines show calculated ratio of N/Z for the given distribution. See text for more details.

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