Prescission charged particle emission inF19+232

Abstract

The multiplicities of prescission protons and n particles in the reaction ' F+ Th at 104, 110, 116, and 118 MeV have been measured. The observed multiplicities are much larger than the prediction of the statistical model without the introduction of fission delay. An analysis of the prescission proton and u data along with that for neutrons (measured earlier) has been made using deformed optical model and deformation-dependent particle binding energies. Simultaneous fits to the charged particle and neutron data required a total fission time scale in the range of (25 -80)X 10 ' s. For this system, the mean kinetic energies of the prescission particles are insensitive to the division of the total delay time into presaddle and postsaddle components; however, the neutron and charged particle multiplicity data are sensitive to the deformation of the saddle-to-scission emitter.The analysis shows that postsaddle emission takes place close to the scission point. PACS number(s): 25.70.Jj, 25.85.6e

Evaporation and fission decay of 132Ce compound nuclei at Ex=122 MeV: some limitations of the statistical model

“…These ingredients involve the level density, the trasmission coefficients and the fission barrier models. Furthermore, estimates of τ d ,o rt h e fission time scale of the specific model, are often quite blurred by the fact that different sets of input parameters provide equally good fit to the data within the same model [3,9,10].…”

“…The Statistical Model (SM) is widely used to support the picture of a heavy-ion-induced fission process governed by nuclear viscosity [1][2][3][4][5][6][7][8][9][10][11][12]. The excess of measured prescission light particles and GDR γ-rays multiplicities with respect to the expected values determined by the SM is usually ascribed to the increment of the lifetime of the hot fissioning nucleus because of the viscosity of the nuclear matter, a physical ingredient not included in the SM.…”

Fission Dynamics: The Quest of a Temperature Dependent Nuclear Viscosity

“…In spite of the extensive work, estimates of the fission time scales are however quite controversial, ranging from 5 to 500 × 10 −21 s, depending on the system and on the experimental probe. Furthermore, such estimates are weakened by the fact that different sets of input parameters can result in equally good fits within the same model [3,4,7].…”

“…A large variety of studies [1][2][3][4][5][6][7][8][9][10] on the fission decay of composite systems with A≈180-250 has shown that the pre-scission multiplicities of neutrons and charged particles increase monotonically with the bombarding energy in contrast with the calculations of the statistical model (SM). This finding is considered as the evidence that fission is a slow process with respect to the lifetime for the emission of light particles.…”

Study of nuclear fusion-fission dynamics in 16O+194Pt reaction

“…Depending upon the excitation energy, temperature, and angular momentum, the CN may tend towards the fission process [3]. Detection of charged particles as well as neutrons is used as a probe to investigate the statistical and dynamical processes of the excited nucleus [4]. The total energy carried away by the emitted particle will depend upon the Q-value and the kinetic energy of the fission fragments.…”