A new formula for the saddle-to-scission time

Boilley, David; Marchix, A.; Jurado, B.; Schmidt, K.

doi:10.1140/epja/i2007-10415-5

Cited by 10 publications

(9 citation statements)

References 27 publications

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“…* Electronic address : schmitt@ganil.fr commonly called the transient time τ trans [2, 3] 1 . Beyond the saddle, Coulomb repulsion drives the nucleus to more elongated shapes until it splits into two fragments and dissipative phenomena are dominated by friction which increases the saddle-to-scission time τ ss [13,14,15]. Although the very nature of nuclear dissipation remains an open question [16,17,18,19,20], its influence on the total fission time is well-established [21].…”

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confidence: 99%

Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission

Schmitt

Schmidt²,

Kelić³

et al. 2010

Phys. Rev. C

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38 pages, 15 figuresPeripheral collisions with radioactive heavy-ion beams at relativistic energies are discussed as an innovative approach for probing the transient regime experienced by fissile systems evolving towards quasi-equilibrium. A dedicated experiment using the advanced technical installations of GSI, Darmstadt, permitted to realize ideal conditions for the investigation of relaxation effects in the meta-stable well. Combined with a highly sensitive experimental signature, it provides a measure of the transient effects with respect to the flux over the fission barrier. Within a two-step reaction process, 45 proton-rich unstable spherical isotopes produced by projectile-fragmentation of a stable 238U beam have been used as secondary projectiles. The fragmentation of the radioactive projectiles on lead results in nearly spherical compound nuclei which span a wide range in excitation energy and fissility. The decay of these excited systems by fission is studied with a dedicated set-up which permits the detection of both fission products in coincidence and the determination of their atomic numbers with high resolution. The width of the fission-fragment nuclear charge distribution is shown to be specifically sensitive to pre-saddle transient effects and is used to establish a clock for the passage of the saddle point. The comparison of the experimental results with model calculations points to a fission delay of (3.3+/-0.7).10-21s for initially spherical compound nuclei, independent of excitation energy and fissility. This value suggests a nuclear dissipation strength at small deformation of (4.5+/-0.5).1021s-1. The very specific combination of the physics and technical equipment exploited in this work sheds light on previous controversial conclusions

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confidence: 99%

Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission

Schmitt

Schmidt²,

Kelić³

et al. 2010

Phys. Rev. C

Self Cite

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“…A physical understanding for the dependence of N p ( N α ) on deformation is as follows. A higher β leads to a longer saddle-to-scission time [72,73], which will provide more time for particle emission. Moreover, the drop in neutron binding energy becomes larger with increasing deformation.…”

Section: Resultsmentioning

confidence: 99%

Significant role of deformation in probing postsaddle nuclear dissipation with light particle emission

2010

Phys. Rev. C

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Using a one-dimensional Langevin model, we study the effects of deformation on the multiplicities of postsaddle neutrons, protons, α particles, and giant dipole resonance (GDR) γ rays of a heavy fissioning system 240 Cf as probes of postsaddle nuclear dissipation (β). It is shown that postsaddle dissipation effects on these light particles have a significant deformation dependence. Furthermore, we find that the role of deformation depends on the type of the particle. It reduces the sensitive influence of β on protons, α particles, and GDR γ rays substantially, whereas it enhances the sensitivity of neutrons to β. The results suggest that to accurately extract the postsaddle friction strength by comparing measured prescission particle multiplicities of heavy nuclei with calculations based on statistical models or stochastic equations like Langevin equations, it is important to take into account the deformation effects. The influence of model dimensionality is discussed.

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“…where r e is the steady escape rate [1,3,[28][29][30][31][32]. This approximation implies that once the particle passes over the barrier top at last time, it should escape over the barrier with the Karmers decay form.…”

Section: The Modified Barrier Passing Probability and Fusion-fission ...mentioning

confidence: 99%

“…3(a). However, when the temperature is larger than the barrier height, the Kramers rate formula is not applicable, we use the inverse of the mean first passage time (MFPT) [31] across an exit x ex given by…”

Section: The Modified Barrier Passing Probability and Fusion-fission ...mentioning

confidence: 99%

Whole fusion-fission process with Langevin approach and compared with analytical solution for barrier passage

Han¹,

Bao²

2014

Preprint

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We investigate time-dependent probability for a Brownian particle passing over the barrier to stay at a metastable potential pocket against escaping over the barrier. This is related to whole fusion-fission dynamical process and can be called the reverse Kramers problem. By the passing probability over the saddle point of inverse harmonic potential multiplying the exponential decay factor of a particle in the metastable potential, we present an approximate expression for the modified passing probability over the barrier, in which the effect of reflection boundary of potential is taken into account. Our analytical result and Langevin Monte-Carlo simulation show that the probability passing and against escaping over the barrier is a non-monotonous function of time and its maximal value is less than the stationary result of passing probability over the saddle point of inverse harmonic potential.

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A new formula for the saddle-to-scission time

Cited by 10 publications

References 27 publications

Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission

Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission

Significant role of deformation in probing postsaddle nuclear dissipation with light particle emission

Whole fusion-fission process with Langevin approach and compared with analytical solution for barrier passage

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