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Title: Influence of entrance channel on fusion hindrance and quasi-fission

Abstract

Recent experimental data showing the interplay between fusion hindrance effects and the onset of the quasi-fission mechanism are presented. The aim of such investigations is understanding the role of entrance channel properties on the competing fusion-fission and quasi-fission processes, also in connection with the possible implications for superheavy element production. In this context, the role of mass asymmetry, nuclear deformation and shell effects is discussed.

Authors:
 [1]; ; ; ; ; ; ; ;  [2]; ; ; ; ; ; ;  [3]; ; ;  [4];  [5] more »;  [6] « less
  1. INFN - Sezione di Napoli, I-80126 Napoli, (Italy)
  2. FLNR - JINR, 141980 Dubna (Russian Federation)
  3. INFN - Laboratori Nazionali di Legnaro, I-35020 Legnaro (Padova) (Italy)
  4. Dipartimento di Fisica, I-35131 Padova (Italy)
  5. (Italy)
  6. IReS, IN2P3-CNR/ULP, F-67037 Strasbourg Cedex 2 (France) (and others)
Publication Date:
OSTI Identifier:
21054814
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 884; Journal Issue: 1; Conference: 6. Latin American symposium on nuclear physics and applications, Iguazu (Argentina), 3-7 Oct 2005; Other Information: DOI: 10.1063/1.2710579; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ASYMMETRY; DEFORMED NUCLEI; FISSION; HEAVY ION FUSION REACTIONS; MASS; NUCLEAR DEFORMATION; QUASI-FISSION; SHELL MODELS; TRANSACTINIDE ELEMENTS

Citation Formats

Trotta, M., Kniazheva, G. N., Chizhov, A. Yu., Itkis, I. M., Itkis, M. G., Kondratiev, N. A., Kozulin, E. M., Sagaidak, R. N., Voskressensky, V. M., Stefanini, A. M., Behera, B. R., Corradi, L., Fioretto, E., Gadea, A., Latina, A., Pokrovsky, I. V., Beghini, S., Montagnoli, G., Scarlassara, F., INFN - Sezione di Padova, I-35131 Padova, and Courtin, S.. Influence of entrance channel on fusion hindrance and quasi-fission. United States: N. p., 2007. Web. doi:10.1063/1.2710579.
Trotta, M., Kniazheva, G. N., Chizhov, A. Yu., Itkis, I. M., Itkis, M. G., Kondratiev, N. A., Kozulin, E. M., Sagaidak, R. N., Voskressensky, V. M., Stefanini, A. M., Behera, B. R., Corradi, L., Fioretto, E., Gadea, A., Latina, A., Pokrovsky, I. V., Beghini, S., Montagnoli, G., Scarlassara, F., INFN - Sezione di Padova, I-35131 Padova, & Courtin, S.. Influence of entrance channel on fusion hindrance and quasi-fission. United States. doi:10.1063/1.2710579.
Trotta, M., Kniazheva, G. N., Chizhov, A. Yu., Itkis, I. M., Itkis, M. G., Kondratiev, N. A., Kozulin, E. M., Sagaidak, R. N., Voskressensky, V. M., Stefanini, A. M., Behera, B. R., Corradi, L., Fioretto, E., Gadea, A., Latina, A., Pokrovsky, I. V., Beghini, S., Montagnoli, G., Scarlassara, F., INFN - Sezione di Padova, I-35131 Padova, and Courtin, S.. Mon . "Influence of entrance channel on fusion hindrance and quasi-fission". United States. doi:10.1063/1.2710579.
@article{osti_21054814,
title = {Influence of entrance channel on fusion hindrance and quasi-fission},
author = {Trotta, M. and Kniazheva, G. N. and Chizhov, A. Yu. and Itkis, I. M. and Itkis, M. G. and Kondratiev, N. A. and Kozulin, E. M. and Sagaidak, R. N. and Voskressensky, V. M. and Stefanini, A. M. and Behera, B. R. and Corradi, L. and Fioretto, E. and Gadea, A. and Latina, A. and Pokrovsky, I. V. and Beghini, S. and Montagnoli, G. and Scarlassara, F. and INFN - Sezione di Padova, I-35131 Padova and Courtin, S.},
abstractNote = {Recent experimental data showing the interplay between fusion hindrance effects and the onset of the quasi-fission mechanism are presented. The aim of such investigations is understanding the role of entrance channel properties on the competing fusion-fission and quasi-fission processes, also in connection with the possible implications for superheavy element production. In this context, the role of mass asymmetry, nuclear deformation and shell effects is discussed.},
doi = {10.1063/1.2710579},
journal = {AIP Conference Proceedings},
number = 1,
volume = 884,
place = {United States},
year = {Mon Feb 12 00:00:00 EST 2007},
month = {Mon Feb 12 00:00:00 EST 2007}
}
  • Experimental results on the fusion inhibition effect near the Coulomb barrier due to the onset of the quasi-fission mechanism are presented. The investigation was focused on reactions induced by 48Ca projectiles on different heavy targets and comparing them to reactions induced by light ions such as 12C and 16O leading to the same compound nuclei. Cross sections and angular distributions of evaporation residues and fission fragments have been measured.
  • Heavy ion fusion reactions are characterized by a long dynamical path between capture of the projectile by the target and compound nucleus formation, during which the composite system not only relaxes in several collective degrees of freedom with distinctly different relaxation times but can also deexcite or reseparate. Experimentally, it is not always possible to identify uniquely the reaction products as belonging to the pre- or post-compound nucleus phase of the reaction process. This often leads to apparent anomalies in the interpretation of some of the experimental results in heavy ion reaction studies. The author had conjectured earlier that themore » competition between fission-like reseparation, particle emission and gamma decay during the relaxation of the fused composite system can lead to some of the recently noticed anomalies in the measured fission fragment angular distributions, prefission neutrons, spectra of hard gamma rays, fusion evaporation residue cross sections, etc. It was also proposed that for a direct experimental test of whether a said anomaly is related to the fusion dynamics, one should study its dependence on the entrance channel mass/charge asymmetry across the Businaro-Gallone critical asymmetry. In this talk, the author will review the recent investigations carried out in India in this area and the resulting understanding of the nuclear collective dynamics in heavy ion fusion reactions.« less
  • Prescission neutron multiplicities in fusion-fission reactions of [sup 11]B+[sup 237]Np, [sup 11]B+[sup 232]Th, [sup 12]C+[sup 232]Th, and [sup 16]O+[sup 232]Th, lying on either side of the Businaro-Gallone mass asymmetry ([alpha][sub BG]), have been measured. The present data along with those available in literature for compound systems spanning the fissility range from 0.70 to 0.84 were analyzed in a consistent manner to deduce fusion-fission time scales for all systems. From the systematic behavior of all the data, the three components of total dynamical fusion-fission delay, namely, transient delay, saddle-to-scission delay, and formation delay, have been deduced. It is found that themore » formation delay depends on the entrance channel mass asymmetry relative to Businaro-Gallone point. The variations of the fusion-fission time scales with fissility, ratio of fission barrier to temperature, and entrance channel mass asymmetry have been studied.« less
  • Pre-scission neutron multiplicities are measured for {sup 12}C + {sup 204}Pb and {sup 19}F + {sup 197}Au reactions at laboratory energies of 75-95 MeV for the {sup 12}C beam and 98-118 MeV for the {sup 19}F beam. The chosen projectile-target combinations in the present study lie on either side of the Businaro-Gallone mass asymmetry ({alpha}{sub BG}) and populate the {sup 216}Ra compound nucleus. The dissipation strength is deduced after comparing the experimentally measured neutron yield with the statistical model predictions which contains the nuclear viscosity as a free parameter. Present results demonstrate the combined effects of entrance channel mass asymmetrymore » and the dissipative property of nuclear matter on the pre-scission neutron multiplicity in fusion-fission reactions.« less
  • A two-stage model is developed in order to describe fusion–fission reactions. The process in the course of which colliding ions approach each other is simulated at the first stage, the deformations and relative orientations of the ions being taken into account. The first stage of the calculation is completed as soon as colliding nuclei touch each other. A continuous nuclear system (monosystem) is formed at this instant. The emerging distributions of the angular momenta of this system and of its potential and internal energies at the point of touching are used as input data that are necessary for triggering themore » second stage of the calculation. The evolution of collective coordinates that describe the shape of the monosystem is calculated at the second stage. The description of this evolution is terminated either at the instant of its fission or upon the release of a major part of its excess energy via particle and photon emission. In the latter case, the probability for the fission of the monosystem or a further decrease in its excitation energy becomes extremely small. The ion-collision process and the evolution of the monosystem formed after primary nuclei come into contact are simulated on the basis of stochastic Langevin equations. The quantities appearing in them (which include the potential energy and inertial and friction parameters) are determined with allowance for the shell structure of nuclei. The tunneling of colliding nuclei through the Coulomb barrier is taken into account, and the effect of this phenomenon on model predictions is studied.« less