Fission modes of mercury isotopes

Warda, M.; Staszczak, A.; Nazarewicz, W.

doi:10.1103/physrevc.86.024601

Cited by 104 publications

(119 citation statements)

References 29 publications

(45 reference statements)

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“…The mechanism behind the asymmetric MD is different from that in the uranium region, since strong shell effects in the respective FFs are absent in the neutron-deficient lead region. Several theoretical models reproduced this observation [28][29][30][31]. Extensive calculations of the FF mass yields by use of the recently developed Brownian Metropolis shape-motion treatment [32] are shown in Fig.…”

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confidence: 84%

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Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Ghys¹,

Andreyev²,

Huyse³

et al. 2014

Phys. Rev. C

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Low-energy β-delayed fission of 194,196 At and 200,202 Fr was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei 194,196 Po and 202 Rn indicate a triple-humped structure, marking the transition between asymmetric fission of 178,180 Hg and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy density functional yields discrepancies. This demonstrates once more the need of dynamical fission calculations, as for both models the potential-energy surfaces lack pronounced structures, in contrast to the actinide region.Nuclear fission, the division of a heavy atomic nucleus into predominantly two parts, continues to provide new and unexpected features in spite of a long history of intensive theoretical and experimental studies [1][2][3][4][5][6][7]. The fission process is not only important for several applications, such as energy production and radiopharmacology, but also has a direct impact on the understanding of the fission recycling process in r -process nucleosynthesis [8,9]. Therefore, a description of the fission process with reliable predictive power is needed, in particular for low-energy fission where the fission-fragment (FF) mass distributions are strongly * lars.ghys@fys.kuleuven.be sensitive to microscopic effects [4]. Mass distributions (MDs) are usually predominantly symmetric or asymmetric with the yields exhibiting a single peak or two distinct peaks, respectively. However, in several cases a mixture of two modes was observed [5]. Experimental observables characterizing various fission modes are the width of the MD peak(s), the position of these peaks in asymmetric mass division and total kinetic energy (TKE) of the FFs. The dominance of asymmetric fission in most of the actinide region beyond A = 226 up to about 256 Fm was attributed to strong microscopic effects of the heavier FF, near the doubly-magic 132 Sn [4,10,11]. However, nuclei such as 258 Fm and 259,260 Md exhibit complex MDs, each with a narrow and a broad symmetric component with a higher and lower TKE, respectively. 2This phenomenon is called bimodal fission [12][13][14][15]. Competition between symmetric and asymmetric fission, corresponding to respectively lower and higher TKE and resulting in a triple-humped MD has been reported around 226 Th [16][17][18]. These observations strongly support the hypothesis that nuclei may fission through several independent fission modes corresponding to different pre-scission shapes and fission paths in a multidimensional potential-energy landscape, referred to in literature as multimodal or multichannel fission [4,5,11,[16][17][18][19]. In the pre-actinide region, predominantly symmetric FF mass distributions were measured. A few relevant cases for the present discussion (see also Fig.1) are 195 Au, 198 Hg and 208,210 Po, studied by means of charged-particle induced reactions [20][21][22] and 204,206,...

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confidence: 84%

“…The microscopic HFB theory with Gogny D1S nuclear force [29,48,49], see Fig. 4, shows a broad and flat plateau in the potential-energy surface (PES) with numerous weakly-pronounced valleys and ridges, not exceeding 2 MeV energy difference, for a wide range of quadrupole (beyond Q 2 = 100 b) and octupole defor- (2) a data taken from [27] mations.…”

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confidence: 99%

Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Ghys¹,

Andreyev²,

Huyse³

et al. 2014

Phys. Rev. C

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“…In this work, the mass quadrupole moment Q 20 was used as a driving constraint enumerating consecutive points along the one-dimensional static fission path; all remaining multipole moments representing the multitude of shapes (including triaxial and reflection-asymmetric shapes) on the way to fission are determined selfconsistently. As discussed in our previous studies [12,44], exploring many collective coordinates makes it possible to identify saddle points and valleys [11,45,46] as the competing fission pathways associated with adiabatically-varied configurations are well separated in the collective space when studied in more than one dimension. To eliminate discontinuities in the self-consistent potential energy surfaces [46] in the vicinity of the saddle points, we locally carried out calculations with two constraints: Q 20 (elongation) and Q 22 (triaxiality).…”

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confidence: 99%

Spontaneous fission modes and lifetimes of superheavy elements in the nuclear density functional theory

2013

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Background: The reactions with the neutron-rich 48 Ca beam and actinide targets resulted in detection of new super-heavy (SH) nuclides with Z = 104 − 118. The unambiguous identification of the new isotopes, however, still poses a problem because their α-decay chains terminate by spontaneous fission (SF) before reaching the known region of the nuclear chart. The understanding of the competition between α-decay and SF channels in SH nuclei is, therefore, of crucial importance for our ability to map the SH region and assess its extent.Purpose: We perform self-consistent calculations of the competing decay modes of even-even SH isotopes with 108 ≤ Z ≤ 126 and 148 ≤ N ≤ 188. Methods:We use the state-of-the-art computational framework based on self-consistent, symmetry-unrestricted nuclear density functional theory capable of describing the competition between nuclear attraction and electrostatic repulsion. We apply the SkM* Skyrme energy density functional. The collective mass tensor of the fissioning superfluid nucleus is computed by means of the cranking approximation to the adiabatic time-dependent Hartree-Fock-Bogoliubov (HFB) approach. This work constitutes the very first systematic self-consistent study of spontaneous fission in the SH region, carried out at a full HFB level, that simultaneously takes into account both triaxiality and reflection asymmetry.Results: Breaking axial symmetry and parity turns out to be crucial for a realistic estimate of collective action; it results in lowering SF lifetimes by more than seven orders of magnitude in some cases. We predict two competing SF modes: reflection-symmetric and reflection-asymmetric. Conclusions:The shortest-lived SH isotopes decay by SF; they are expected to lie in a narrow corridor formed by 280 Hs, 284 Fl, and 284 118 Uuo that separates the regions of SH nuclei synthesized in "cold fusion" and "hot fusion" reactions. The region of long-lived SH nuclei is expected to be centered on 294 Ds with a total half-life of ∼1.5 days. Our survey provides a solid benchmark for the future improvements of self-consistent SF calculations in the region of SH nuclei.

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“…The previous investigations performed with this model proven, that it describes with reasonable accuracy the experimental data of the most relevant properties of unstable nuclei for different decay modes, such as spontaneous fission [17,18,19,20] and exotic process of cluster radioactivity [22]. Also the asymmetric fission of 180 Hg isotope was successfully explained within microscopic approach [23]. In this paper detailed analysis of the scission point configuration determined in the microscopic calculations is performed.…”

Section: Introductionmentioning

confidence: 99%

Fission fragment mass yield deduced from density distribution in the pre-scission configuration

Warda

Zdeb

2015

Phys. Scr.

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Abstract. Static self-consistent methods usually allow to determine the most probable fission fragments mass asymmetry. We have applied random neck rupture mechanism to the nuclei in the configuration at the end of fission paths. Fission fragment mass distributions have been deduced from the prescission nuclear density distribution obtained from the self-consistent calculations. Potential energy surfaces as well as nuclear shapes have been calculated in the fully microscopic theory, namely the constrained Hartree-Fock-Bogolubov model with the effective Gogny D1S density-dependent interaction. The method has been applied for analysis of fission of 256,258 Fission fragment mass yield deduced from density distribution in the pre-scission configuration 2

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Fission modes of mercury isotopes

Cited by 104 publications

References 29 publications

Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Evolution of fission-fragment mass distributions in the neutron-deficient lead region

Spontaneous fission modes and lifetimes of superheavy elements in the nuclear density functional theory

Fission fragment mass yield deduced from density distribution in the pre-scission configuration

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