The contrasting fission potential-energy structure of actinides and mercury isotopes

Abstract

Fission-fragment mass distributions are asymmetric in fission of typical actinide nuclei for nucleon number $A$ in the range $228⋦A⋦258$ and proton number $Z$ in the range $90⋦Z⋦100$. For somewhat lighter systems it has been observed that fission mass distributions are usually symmetric. However, a recent experiment showed that fission of ${}^{180}$Hg following electron capture on ${}^{180}$Tl is asymmetric. We calculate potential-energy surfaces for a typical actinide nucleus and for 12 even isotopes in the range ${}^{178}$Hg--${}^{200}$Hg, to investigate the similarities and differences of actinide compared to mercury potential surfaces and to what extent fission-fragment properties, in particular shell structure, relate to the structure of the static potential-energy surfaces. Potential-energy surfaces are calculated in the macroscopic-microscopic approach as functions of fiveshape coordinates for more than five million shapes. The structure of the surfaces are investigated by use of an immersion technique. We determine properties of minima, saddle points, valleys, and ridges between valleys in the 5D shape-coordinate space. Along the mercury isotope chain the barrier heights and the ridge heights and persistence with elongation vary significantly and show no obvious connection to possible fragment shell structure, in contrast to the actinide region, where there is a deep asymmetric valley extending from the saddle point to scission. The mechanism of asymmetric fission must be very different in the lighter proton-rich mercury isotopes compared to the actinide region and is apparently unrelated to fragment shell structure. Isotopes lighter than ${}^{192}$Hg have the saddle point blocked from a deep symmetric valley by a significant ridge. The ridge vanishes for the heavier Hg isotopes, for which we would expect a qualitatively different asymmetry of the fragments.

8 pages, 9 figures

References in corpus (4)

• Microscopic approach of fission dynamics applied to fragment kinetic energy and mass distributions in 238U
• Brownian shape motion on five-dimensional potential-energy surfaces: Nuclear fission-fragment mass distributions
• Five-Dimensional Fission-Barrier Calulations from Se-70 to Cf-252
• Origin of the narrow, single peak in the fission-fragment mass distribution for ${}^{258}$Fm

Cited by in corpus (16)

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• Multidimensionally-constrained relativistic mean-field study of triple-humped barriers in actinides
• First observation of the competing fission modes in the neutron-deficient sub-lead region
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• The impact of the surface energy coefficient on the deformation properties of atomic nuclei as predicted by Skyrme energy density functionals
• Nuclear Quantum Many-Body Dynamics: From Collective Vibrations to Heavy-Ion Collisions (2nd edition)
• ${}^{178}$Hg and asymmetric fission of neutron-deficient pre-actinides
• Collinear cluster tri-partition: Kinematics constraints and stability of collinearity
• Semiclassical trace formula for truncated spherical well potentials: Toward the analyses of shell structures in nuclear fission processes
• Nascent fragment shell effects on the nuclear fission processes in semiclassical periodic orbit theory
• Three-dimensional potential energy surface for fission of ${}^{236}$U within covariant density functional theory
• Semiclassical origin of asymmetric nuclear fission: Nascent-fragment shell effect in periodic-orbit theory
• Shell effects in quasifission toward ${}^{180}\mathrm{Hg}$: insights into fission asymmetric modes