Exploring the multihumped fission barrier of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow /><mml:mn>238</mml:mn></mml:msup></mml:math>U via sub-barrier photofission

Csige, L.; Filipescu, D.; Glodariu, T.; Gulyás, J.; Günther, M.; Habs, D.; Karwowski, H. J.; Krasznahorkay, A.; Rich, G. C.; Sin, M.; Stroe, L.; Tešileanu, O.; Thirolf, P. G.

doi:10.1103/physrevc.87.044321

Cited by 46 publications

(57 citation statements)

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“…For example Blons and collaborators [40] consistently find that the so called "third minima" of some light actinide nuclei are very shallow and no more than 0.5 MeV or so below the surrounding second and third barrier peaks, which are about 6 MeV above the ground-state minimum, in good agreement with results obtained in our current model [41]. In contrast, Csige and collaborators [42][43][44] find third minima for nuclei in this region that are up to 3 MeV below the surrounding peaks. We find it difficult to reconcile with potential-energy calculations the substantial difference in barrier structure they find between 232 92 U 140 [42] and 232 91 Pa 141 [43] in these studies.…”

Section: Resultscontrasting

confidence: 34%

Fission barriers at the end of the chart of the nuclides

et al. 2015

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We present calculated fission-barrier heights for 5239 nuclides, for all nuclei between the proton and neutron drip lines with 171 ≤ A ≤ 330. The barriers are calculated in the macroscopicmicroscopic finite-range liquid-drop model (FRLDM) with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than five million different shapes, defined by five deformation parameters in the threequadratic-surface shape parameterization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ǫ) and in the spherical-harmonic (β) parameterizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ǫ, γ) parameterization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about one MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative, and when possible, quantitative agreement and/or consistency with data on β-delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. These studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.

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Section: Resultscontrasting

confidence: 34%

Fission barriers at the end of the chart of the nuclides

et al. 2015

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“…[81]. In light of the recent experiment on 238 U [82], it would be particularly interesting to extend this study to heavier isotopes of uranium and thorium. …”

Section: Discussionmentioning

confidence: 99%

Third minima in thorium and uranium isotopes in a self-consistent theory

2013

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Background: Well-developed third minima, corresponding to strongly elongated and reflection-asymmetric shapes associated with dimolecular configurations, have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential energy surfaces in the third minimum region.Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular (cluster) states. We study the isentropic potential energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects. Methods:We use the finite-temperature superfluid nuclear density functional theory. We consider two Skyrme energy density functionals: a traditional functional SkM * and a recent functional UNEDF1 optimized for fission studies.Results: We predict very shallow or no third minima in the potential energy surfaces of 232 Th and 232 U. In the lighter Th and U isotopes with N = 136 and 138, the third minima are better developed. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly-magic 132 Sn and a lighter deformed Zr or Mo fragment. The potential energy surfaces for 228,232 Th and 232 U at several excitation energies are presented. We also study isotopic chains to demonstrate the evolution of the depth of the third minimum with neutron number. Conclusions:We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr and Mo isotopes around N = 58. We demonstrate that the depth of the third minimum is sensitive to the excitation energy of the nucleus. In particular, the thermal reduction of pairing, and related enhancement of shell effects, at small excitation energies help to develop deeper third minima. At large excitation energies, shell effects are washed out and third minima disappear altogether.

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“…Thus, the excitation energy along the fission path is lower than for most of the other systems. Secondly, there are indications that the fission barriers of the nuclei in this region have a complex structure with several consecutive saddle points [187,188], whereby the height of the third barrier, relative to the inner saddles, grows towards lighter nuclei. Considering that the system 238 U(sf) that probably has an even lower excitation energy along the fission path than 229 Th(n th ,f) does not show the anomaly in the inner wings of the mass distribution, it seems tempting to attribute this anomaly to the influence of the third barrier on the evolution of the mass-asymmetry degree of freedom.…”

Section: Discussionmentioning

confidence: 99%

General Description of Fission Observables: GEF Model Code

Schmidt

Jurado

Amouroux

et al. 2016

Nuclear Data Sheets

445

421

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The GEF ("GEneral description of Fission observables") model code is documented. It describes the observables for spontaneous fission, neutron-induced fission and, more generally, for fission of a compound nucleus from any other entrance channel, with given excitation energy and angular momentum. The GEF model is applicable for a wide range of isotopes from Z = 80 to Z = 112 and beyond, up to excitation energies of about 100 MeV. The results of the GEF model are compared with fission barriers, fission probabilities, fission-fragment mass-and nuclide distributions, isomeric ratios, total kinetic energies, and prompt-neutron and prompt-gamma yields and energy spectra from neutron-induced and spontaneous fission. Derived properties of delayed neutrons and decay heat are also considered.The GEF model is based on a general approach to nuclear fission that explains a great part of the complex appearance of fission observables on the basis of fundamental laws of physics and general properties of microscopic systems and mathematical objects. The topographic theorem is used to estimate the fission-barrier heights from theoretical macroscopic saddle-point and ground-state masses and experimental ground-state masses. Motivated by the theoretically predicted early localisation of nucleonic wave functions in a necked-in shape, the properties of the relevant fragment shells are extracted. These are used to determine the depths and the widths of the fission valleys corresponding to the different fission channels and to describe the fission-fragment distributions and deformations at scission by a statistical approach. A modified composite nuclear-level-density formula is proposed. It respects some features in the superfluid regime that are in accordance with new experimental findings and with theoretical expectations. These are a constant-temperature behaviour that is consistent with a considerably increased heat capacity and an increased pairing condensation energy that is consistent with the collective enhancement of the level density. The exchange of excitation energy and nucleons between the nascent fragments on the way from saddle to scission is estimated according to statistical mechanics. As a result, excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment in the superfluid regime. This description reproduces some rather peculiar observed features of the prompt-neutron multiplicities and of the even-odd effect in fission-fragment Z distributions. For completeness, some conventional descriptions are used for calculating pre-equilibrium emission, fission probabilities and statistical emission of neutrons and gamma radiation from the excited fragments. Preference is given to simple models that can also be applied to exotic nuclei compared to more sophisticated models that need precise empirical input of nuclear properties, e.g. spectroscopic information.The approach reveals a high degree of regularity and provides a considerable insight into the physics of the fission process. Fission obs...

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Exploring the multihumped fission barrier of238U via sub-barrier photofission

Cited by 46 publications

References 31 publications

Fission barriers at the end of the chart of the nuclides

Fission barriers at the end of the chart of the nuclides

Third minima in thorium and uranium isotopes in a self-consistent theory

General Description of Fission Observables: GEF Model Code

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