Nuclear deformation in excited Pb isotopes from giant dipole γ-ray-fission angular correlations

Butsch, R.; Thoennessen, M.; Chakrabarty, D. R.; Herman, M.; Paul, P.

doi:10.1103/physrevc.41.1530

Cited by 60 publications

(28 citation statements)

References 34 publications

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“…Typically, for low spins, the production of an evaporation residue dominates while for high spins fission will become the dominant exit channel [25]. Hence, by gating on evaporation residues or fission fragments, one effectively selects a spin region from which high-energy γ emission is observed [26]. In the case of the fission exit channel, one also observes high-energy γ emission from the fission fragments themselves [27], though typically at significantly higher γ energies owing to the much lower mass of the fission fragments.…”

Section: Experimental Techniquesmentioning

confidence: 99%

Compilation of giant electric dipole resonances built on excited states

Schiller

Thoennessen

2007

Atomic Data and Nuclear Data Tables

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Section: Experimental Techniquesmentioning

confidence: 99%

Compilation of giant electric dipole resonances built on excited states

Schiller

Thoennessen

2007

Atomic Data and Nuclear Data Tables

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“…Specifically, careful analyses of experimental values of multiplicities of pre-scission light particles (mainly neutrons and γ 's) [1][2][3][4][5][6][7][8], evaporation residue cross sections [9][10][11] and mass and kinetic energy distributions of fission fragments [1][2][3] have established that the fission dynamics of a hot compound nucleus is dissipative in nature. The theoretical analyses are usually performed either by employing the Langevin equation in a dynamical model of nuclear fission [12][13][14] or by using the statistical model where the fission width includes the effects of dissipation [15].…”

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confidence: 99%

Spin dependence of the modified Kramers width of nuclear fission

Sadhukhan

Pal

2008

Phys. Rev. C

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A statistical model calculation for the decay of a compound nucleus is presented where the compound nuclear spin dependence of the Kramers modified fission width is included. Specifically, the spin dependences of the frequencies of the harmonic oscillator potentials osculating the rotating liquid-drop model potential at equilibrium and saddle regions are considered. Results for the 16 O+ 208 Pb system show that the energy dependence of the dissipation strength extracted from fitting experimental data is substantially reduced when the spin dependence of the frequencies is properly taken into account.During the last two decades, experimental and theoretical investigations of heavy ion induced fusion-fission reactions at beam energies above Coulomb barriers have made significant contributions to the understanding of the nuclear bulk dynamics at high excitation energies. Specifically, careful analyses of experimental values of multiplicities of pre-scission light particles (mainly neutrons and γ 's) [1-8], evaporation residue cross sections [9-11] and mass and kinetic energy distributions of fission fragments [1][2][3] have established that the fission dynamics of a hot compound nucleus is dissipative in nature. The theoretical analyses are usually performed either by employing the Langevin equation in a dynamical model of nuclear fission [12][13][14] or by using the statistical model where the fission width includes the effects of dissipation [15]. The later approach is used more frequently [6-9,11] since it is rather straightforward to implement it in a standard statistical model code for the decay of a compound nucleus.Considering fission as a diffusive process of a Brownian particle across the fission barrier in a viscous medium, Kramers solved the corresponding Fokker-Planck equation with a few simplifying approximations which finally yielded the so-called Kramers modified Bohr-Wheeler expression for fission width as [15,16] whereIn the above, BW is the fission width due to Bohr and Wheeler [17] and β is the strength of the reduced dissipation coefficient. ω gs and ω sad are the local frequencies of the harmonic oscillator potentials which osculate the liquid drop model nuclear potential at the ground state and the saddle configurations, respectively, while m gs and m sad are the corresponding inertia parameters. T is the nuclear temperature. The dimensionless quantity η = β/2ω sad is often used as a free parameter in order to fit experimental data. * Corresponding author: santanu@veccal.ernet.in A number of assumptions are usually made while applying Eq. (1) in statistical model calculations. A constant value for the parameter η is usually assumed for all spin values of the compound nucleus (CN). The centrifugal barrier however changes the potential profile at higher values of spin of a CN, which consequently results in a spin dependence of the frequencies ω gs and ω sad of the osculating harmonic oscillator potentials [18]. Figure 1 shows the frequencies as a function of spin for the compound nucleus 224 Th. ...

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“…It is important to note that light lead isotopes 196−200 Pb are predicted to be superdeformed above a spin of about 20h [21]. Giant dipole resonance measurements performed for the 200 Pb compound system at excitation energy of about ∼70-100 MeV in coincidence with fission fragments seem to demonstrate that nuclei in the pre-scission channel exhibit a deformation parameter β∼0.4 close to the value β=0.6 characteristic of the cold superdeformed shape [22]. It is therefore possible to correlate, at least qualitatively, the findings of the present work with the GDR results.…”

Section: Discussionmentioning

confidence: 95%

Alpha particle emission from the 198Pb compound nucleus: comparison between the fusion-evaporation and the pre-scission channels

Vardaci

Rana

Brondi

et al. 1998

EPJ A

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The alpha-particle emission from the Si-28+Er-170 fusion-evaporation reaction at 165 and 185 MeV has been measured and compared with published data relative to the pre-scission emission in the same reaction. The spectra in the two channels exhibit nearly the same shape in the low energy region, whereas in the high energy region the spectrum for the fusion-evaporation case features a larger apparent temperature. The interpretation of the difference in shape between the two decay channels is based on statistical model calculations which account for the effects due to the different length of the decay chain. Statistical model calculations with standard parameters describe well the gross features of the alpha particle spectra in the fusion-evaporation channel and the proton spectra in the pre-scission channel. On the contrary, the model predictions seem to overestimate by similar or equal to 2 MeV the emission barrier for the alpha particles in the pre-fission channel. This effect is ascribed to the larger elongation of the nucleus during the fission process. An average axis ratio b/a similar to 2 for the emitter is suggested

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Nuclear deformation in excited Pb isotopes from giant dipole γ-ray-fission angular correlations

Cited by 60 publications

References 34 publications

Compilation of giant electric dipole resonances built on excited states

Compilation of giant electric dipole resonances built on excited states

Spin dependence of the modified Kramers width of nuclear fission

Alpha particle emission from the 198Pb compound nucleus: comparison between the fusion-evaporation and the pre-scission channels

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