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

Abstract

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]more » 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.« less

Authors:

Ichikawa, T.; Möller, P.

Publication Date:

Fri Feb 01 00:00:00 EST 2019

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1488372

Alternate Identifier(s):

OSTI ID: 1558050

Report Number(s):

LA-UR-18-28314
Journal ID: ISSN 0370-2693; S0370269318309614; PII: S0370269318309614

Grant/Contract Number:  

AC52-06NA25396; 89233218CNA000001

Resource Type:

Published Article

Journal Name:

Physics Letters B

Additional Journal Information:

Journal Name: Physics Letters B Journal Volume: 789 Journal Issue: C; Journal ID: ISSN 0370-2693

Publisher:

Elsevier

Country of Publication:

Netherlands

Language:

English

Subject:

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