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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:
 [1];  [2]
  1. Kyoto Univ. (Japan)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); P. Moller Scientific Computing and Graphics, Inc., Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (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
Grant/Contract Number:  
89233218CNA000001; AC52-06NA25396
Resource Type:
Journal Article: Published Article
Journal Name:
Physics Letters B
Additional Journal Information:
Journal Volume: 789; Journal Issue: C; Journal ID: ISSN 0370-2693
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; Fission; Fission-fragment mass asymmetry; Single-particle levels

Citation Formats

Ichikawa, Takatoshi, and Möller, Peter. The microscopic mechanism behind the fission-barrier asymmetry (II): The rare-earth region 50 < Z < 82 and 82 < N < 126. United States: N. p., 2018. Web. doi:10.1016/j.physletb.2018.12.034.
Ichikawa, Takatoshi, & Möller, Peter. The microscopic mechanism behind the fission-barrier asymmetry (II): The rare-earth region 50 < Z < 82 and 82 < N < 126. United States. doi:10.1016/j.physletb.2018.12.034.
Ichikawa, Takatoshi, and Möller, Peter. Wed . "The microscopic mechanism behind the fission-barrier asymmetry (II): The rare-earth region 50 < Z < 82 and 82 < N < 126". United States. doi:10.1016/j.physletb.2018.12.034.
@article{osti_1488372,
title = {The microscopic mechanism behind the fission-barrier asymmetry (II): The rare-earth region 50 < Z < 82 and 82 < N < 126},
author = {Ichikawa, Takatoshi and Möller, Peter},
abstractNote = {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.},
doi = {10.1016/j.physletb.2018.12.034},
journal = {Physics Letters B},
issn = {0370-2693},
number = C,
volume = 789,
place = {United States},
year = {2018},
month = {12}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.physletb.2018.12.034

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Cited by: 3 works
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Figures / Tables:

Fig. 1 Fig. 1: Calculated symmetric-yield to peak-yield ratios for 987 fissioning systems. Black squares (open in colored regions, filled outside) indicate β-stable nuclei. From Ref. [22] where the results in the figure are further discussed.

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.