The microscopic mechanism behind the fission-barrier asymmetry (II): The rare-earth region 50 < Z < 82 and 82 < N < 126

Journal Article · Fri Feb 01 00:00:00 EST 2019 · Physics Letters B

DOI:https://doi.org/10.1016/j.physletb.2018.12.034· OSTI ID:1488372

Ichikawa, T.; Möller, P.

It is understood that most actinides fission into fragments of unequal size. This contradicts liquid-drop-model theory from which symmetric fission is expected. The first attempt to understand this difference suggested that division leading to one of the fragments being near doubly magic ¹³²Sn is favored by gain in binding energy. After the Strutinsky shell-correction method was developed an alternative idea that gained popularity was that the fission saddle might be lower for mass-asymmetric shapes and that this asymmetry was preserved until scission. Recently it was determined [Phys. Rev. Lett. 105 (2010) 252502] that ¹⁸⁰Hg preferentially fissions asymmetrically in contradiction to the fragment-magic-shell expectation which suggested symmetric division peaked around ⁹⁰Zr, with its magic neutron number , so it was presented as a “new type of asymmetric fission”. However, in a paper [Phys. Lett. B 34 (1971) 349] a “simple” microscopic mechanism behind the asymmetry of the actinide fission saddle points was proposed to be related to the coupling between levels of type [40ΛΩ] and [51ΛΩ]. The paper then generalizes this idea and made the remarkable prediction that analogous features could exist in other regions. In particular it was proposed that in the rare-earth region couplings between levels of type [30ΛΩ] and [41ΛΩ] would favor mass-asymmetric outer saddle shapes. In this picture the asymmetry of ¹⁸⁰Hg is not a “new type of asymmetric fission” but of analogous origin as the asymmetry of actinide fission. This prediction has never been cited in the discussion of the recently observed fission asymmetries in the “new region of asymmetry”, in nuclear physics also referred to as the rare-earth region. We reflect by detailed analysis that the mechanism of the saddle asymmetry in the sub-Pb region is indeed the one predicted half a century ago.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-06NA25396; 89233218CNA000001
• OSTI ID: 1488372
• Alternate ID(s): OSTI ID: 1558050
• Report Number(s): LA-UR-18-28314; S0370269318309614; PII: S0370269318309614
• Journal Information: Physics Letters B, Journal Name: Physics Letters B Vol. 789 Journal Issue: C; ISSN 0370-2693
• Publisher: Elsevier
• Country of Publication: Netherlands
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
Fission
Fission-fragment mass asymmetry
Single-particle levels