Entrance channel effects in the fusion-fission time scales from studies of prescission neutron multiplicities

Saxena, A.; Chatterjee, A.; Choudhury, R. K.; Kapoor, S. S.; Nadkarni, D.M.

doi:10.1103/physrevc.49.932

Cited by 125 publications

(64 citation statements)

References 29 publications

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“…Primarily this task becomes one of identifying quasifission, the re-separation of the contacting nuclei before moving inside the fission saddle point. There the product of the atomic numbers of the reacting nuclei, Z 1 Z 2 , exceeds 1600 [1,16,[18][19][20][21] and (c) when the asymmetry, α, of the reacting system is less than the mass asymmetry associated with the Businaro-Gallone point [22][23][24][25][26]. Unfortunately there are known exceptions to each of these general rules, i.e., (a) [24,27,28] (b) [29][30][31] (c) [31,32].…”

Section: B Reaction Mechanismsmentioning

confidence: 99%

Measurement of the fusion probability,PCN, for hot fusion reactions

et al. 2013

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Background: The cross section for forming a heavy evaporation residue in fusion reactions depends on the capture cross section, the fusion probability, P CN , i.e., the probability that the projectile-target system will evolve inside the fission saddle point to form a completely fused system rather than re-separating (quasifission), and the survival of the completely fused system against fission. P CN is the least known of these quantities. Methods: We measured the fission fragment angular distributions for these reactions and used the formalism of Back to deduce the fusion-fission and quasifission cross sections. From these quantities we deduced P CN for each reaction. Conclusions:The new measured values of P CN agree roughly with the semi-empirical systematic dependence of P CN upon fissility for excited nuclei.

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Section: B Reaction Mechanismsmentioning

confidence: 99%

Measurement of the fusion probability,PCN, for hot fusion reactions

et al. 2013

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“…(12)). The effect of damping manifests itself in the hindrance of the fission mode as compared to the particle emission channels and therefore, in anomalously large pre-scission particle multiplicities in the fission process [5,[17][18][19][20]. The observed excess in the pre-scission particle multiplicities has been used to deduce the dynamical delay in the fission decay arising due to coupling of the intrinsic excitation energy to the collective kinetic energy in the fission mode.…”

Section: Heavy Ion Fusion-fission Excitation Functionsmentioning

confidence: 97%

“…This has significance for the direction of mass drift between the two sides of a dinuclear system produced in a heavy ion collision process. While the exact dynamical path of mass equilibration followed by the system is governed by both the potential energy and the initial kinetics of the many body nuclear system, the influence of BG point in the fusion-fission time scales and shape equilibration has been demonstrated in many recent experiments and by the detailed dynamical calculations [5,6]. In the present review, we shall deal with some selected aspects of heavy ion induced fission reactions with special emphasis on our recent experimental findings, which have important implications on the dynamics of the fusion-fission process.…”

Section: Introductionmentioning

confidence: 99%

Recent studies in heavy ion induced fission reactions

Choudhury

2001

Pramana - J Phys

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Nuclear fission process involves large scale shape changes of the nucleus, while it evolves from a nearly spherical configuration to two separated fission fragments. The dynamics of these shape changes in the nuclear many body system is governed by a strong interplay of the collective and single particle degrees of freedom. With the availability of heavy ion accelerators, there has been an impetus to study the nuclear dynamics through the investigations of nucleus-nucleus collisions involving fusion and fission process. From the various investigations carried out in the past years, it is now well recognized that there is large scale damping of collective modes in heavy ion induced fission reactions, which in other words implies that nuclear motion is highly viscous. In recent years, there have been many experimental observations in heavy ion induced fission reactions at medium bombarding energies, which suggest possible occurrence of various non-equilibrium modes of fission such as quasi-fission, fast fission and pre-equilibrium fission, where some of the internal degrees of freedom of the nucleus is not fully equilibrated. We have carried out extensive investigations on the fission fragment angular distributions at near barrier bombarding energies using heavy fissile targets. The measured fragment anisotropies when compared with the standard saddle point model (SSPM) calculations show that for projectile-target systems having zero or low ground state spins, the angular anisotropy exhibits a peak-like behaviour at the sub barrier energies, which cannot be explained by the SSPM calculations. For projectiles or targets with large ground state spins, the anomalous peaking gets washed out due to smearing of the Ã-distribution by the intrinsic entrance channel spins. Recently studies have been carried out on the spin distributions of fission fragments through the gamma ray multiplicity measurements. The fission fragments acquire spin mainly from two sources: (i) due to rigid rotation of the nascent fragments at scission and (ii) due to statistical excitation of the spin bearing collective modes in the fissioning nucleus. One of the collective modes -the tilting mode depends on the Ã quantum number and is responsible for the emission angle dependence of fragment spin. In our studies, we have shown conclusively that the collective statistical spin modes get strongly suppressed for high Ã values corresponding to large rotational frequencies along the fission axis. These results bring out the importance of the dynamical effects in the heavy ion induced fusion-fission reactions. The present article will review the work carried out on the above aspects in heavy ion fission reactions as well as on the fission time scales, and some of the recent studies on the mass-energy correlations of fission fragments at near-barrier bombarding energies.

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“…The experimental observations of large scale damping of the collective modes in fission process leading to large dynamical delays in fission decay have led to extensive studies earlier in this field [1][2][3][4]. Recently, there have been observations of anomalous anisotropies in the angular distributions of the fission fragments in comparison to the standard saddle point statistical model (SSPSM) predictions in a large number of target-projectile systems.…”

Section: Introductionmentioning

confidence: 99%

Some aspects of heavy ion fusion-fission dynamics

et al. 1999

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Study of heavy ion induced fusion-fission reactions at near and below barrier energies has attracted a great deal of attention in recent years, due to the observations of anomalous features in the fragment angular distributions for many target-projectile systems. Additionally there are also measurements of the fragment spin distributions and time-scales of the fusion-fission reactions, which have provided important information on the dynamics of these processes. In the present paper, the emphasis would be to highlight some of the recent experimental findings and their implications on the dynamics of the fusion-fission reactions in heavy ion collisions at near and above barrier energies.

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Entrance channel effects in the fusion-fission time scales from studies of prescission neutron multiplicities

Cited by 125 publications

References 29 publications

Measurement of the fusion probability,PCN, for hot fusion reactions

Measurement of the fusion probability,PCN, for hot fusion reactions

Recent studies in heavy ion induced fission reactions

Some aspects of heavy ion fusion-fission dynamics

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