The microscopic mechanism behind the fission barrier asymmetry

We first give an overview of the shell-correction method which was developed by V. M.Strutinsky as a practicable and efficient approximation to the general selfconsistent theory of finite fermion systems suggested by A. B. Migdal and collaborators. Then we present in more detail a semiclassical theory of shell effects, also developed by Strutinsky following original ideas of M. Gutzwiller. We emphasize, in particular, the influence of orbit bifurcations on shell structure. We first give a short overview of semiclassical trace formulae, which connect the shell oscillations of a quantum system with a sum over periodic orbits of the corresponding classical system, in what is usually called the "periodic orbit theory". We then present a case study in which the gross features of a typical double-humped nuclear fission barrier, including the effects of mass asymmetry, can be obtained in terms of the shortest periodic orbits of a cavity model with realistic deformations relevant for nuclear fission. Next we investigate shell structures in a spheroidal cavity model which is integrable and allows for fargoing analytical computation. We show, in particular, how period-doubling bifurcations are closely connected to the existence of the so-called "superdeformed" energy minimum which corresponds to the fission isomer of actinide nuclei. Finally, we present a general class of radial power-law potentials which approximate well the shape of a Woods-Saxon potential in the bound region, give analytical trace formulae for it and discuss various limits (including the harmonic oscillator and the spherical box potentials).

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“…states which microscopically are responsible [63] for the asymmetry effect in the SCM approach (see the schematic plot on the r.h.s. of Fig.…”

Section: Semiclassical Calculation Of a Nuclear Fission Barriermentioning

confidence: 99%

Shell structure and orbit bifurcations in finite fermion systems

et al. 2011

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“…All radiative transitions between the energy levels mentioned above are treated in complete frequency redistribution. Other atoms are treated in LTE with the background opacity package of Gustafsson (1973).…”

Section: Introductionmentioning

confidence: 99%

Non-LTE Calculations of the Fe i 6173 Å Line in a Flaring Atmosphere

Hong

Ding

et al. 2018

ApJL

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The Fe I 6173 Å line is widely used in the measurements of vector magnetic fields by instruments including the Helioseismic and Magnetic Imager (HMI). We perform non-local thermodynamic equilibrium calculations of this line based on radiative hydrodynamic simulations in a flaring atmosphere. We employ both a quiet-Sun atmosphere and a penumbral atmosphere as the initial one in our simulations. We find that, in the quiet-Sun atmosphere, the line center is obviously enhanced during an intermediate flare. The enhanced emission is contributed from both radiative backwarming in the photosphere and particle beam heating in the lower chromosphere. A blue asymmetry of the line profile also appears due to an upward mass motion in the lower chromosphere. If we take a penumbral atmosphere as the initial atmosphere, the line has a more significant response to the flare heating, showing a central emission and an obvious asymmetry. The low spectral resolution of HMI would indicate some loss of information but the enhancement and line asymmetry are still kept. By calculating polarized line profiles, we find that the Stokes I and V profiles can be altered as a result of flare heating. Thus the distortion of this line has a crucial influence on the magnetic field measured from this line, and one should be cautious in interpreting the magnetic transients observed frequently in solar flares.

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“…Closed shells have then been naturally invoked as possible drivers to asymmetric fission [6][7][8][9][10], energetically favouring the formation of fragments with (doubly)magic clusters such as 132 50 Sn 82 . Neutron deformed shell effects in fission fragments with N ≈ 88 neutrons [11] as well as in the fissioning nucleus [12] have also been invoked. However, experiments show that the main driver to asymmetric fission in the actinide region is the number of protons of the heavy fragment, which remains particularly stable around Z ≈ 54 [13][14][15].…”

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Effect of shell structure on the fission of sub-lead nuclei

Scamps

Simenel

2019

Phys. Rev. C

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Fission of atomic nuclei often produce mass asymmetric fragments. However, the origin of this asymmetry was believed to be different in actinides and in the sub-lead region [A. Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010)]. It has recently been argued that quantum shell effects stabilising pear shapes of the fission fragments could explain the observed asymmetries in fission of actinides [G. Scamps and C. Simenel, Nature 564, 382 (2018)]. This interpretation is tested in the sub-lead region using microscopic mean-field calculations of fission based on the Hartree-Fock approach with BCS pairing correlations. The evolution of the number of protons and neutrons in asymmetric fragments of mercury isotope fissions is interpreted in terms of deformed shell gaps in the fragments. A new method is proposed to investigate the dominant shell effects in the pre-fragments at scission. We conclude that the mechanisms responsible for asymmetric fissions in the sub-lead region are the same as in the actinide region, which is a strong indication of their universality.

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The microscopic mechanism behind the fission barrier asymmetry

Cited by 51 publications

References 8 publications

Shell structure and orbit bifurcations in finite fermion systems

Shell structure and orbit bifurcations in finite fermion systems

Non-LTE Calculations of the Fe i 6173 Å Line in a Flaring Atmosphere

Effect of shell structure on the fission of sub-lead nuclei

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