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Title: Experimental studies of quasi-fission reactions

Abstract

A large number of recent experimental studies have shown that a substantial fraction of the total reaction cross section in heavy-ion reactions is found in fission-like processes, which do not result from the fission decay of a completely fused system. Following the suggestion of Swiatecki such processes, which represents a complete relaxation of the relative kinetic energy and a substantial amount of net mass transfer between the two fragments, are denoted quasi-fission reactions. They are distinct from compound fission reactions by bypassing the stage of a completely fused-system. This typically means that they are associated with short reaction times, which results in several measurable characteristics such as broken forward-backward symmetries, large anisotropies of the angular distributions and increased widths of the fragment mass distributions. The distinction between quasi-fission and deep inelastic reactions is less stringent and has the character of a gradual evolution from one reaction type to the other, as found also as quasi-elastic reaction evolves into deeply inelastic processes as a function of the total kinetic energy loss. In the present paper some of the experimental data characterizing quasi-fission reactions are reviewed and discussed. 22 refs., 6 figs.

Authors:
Publication Date:
Research Org.:
Argonne National Lab., IL (USA)
OSTI Identifier:
6573147
Alternate Identifier(s):
OSTI ID: 6573147; Legacy ID: DE89003968
Report Number(s):
CONF-880896-5
ON: DE89003968
DOE Contract Number:
W-31109-ENG-38
Resource Type:
Conference
Resource Relation:
Conference: Symposium on heavy-ion reaction dynamics in tandem energy region, Hitachi, Japan, 1 Aug 1988; Other Information: Portions of this document are illegible in microfiche products
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; LEAD 208 TARGET; HEAVY ION REACTIONS; QUASI-FISSION; SAMARIUM 154 TARGET; THORIUM 232 TARGET; URANIUM 238 TARGET; ANGULAR DISTRIBUTION; ANGULAR MOMENTUM; DEEP INELASTIC SCATTERING; EXPERIMENTAL DATA; FISSION FRAGMENTS; FLUORINE 19 REACTIONS; MAGNESIUM 24 REACTIONS; MASS DISTRIBUTION; NICKEL 60 REACTIONS; OXYGEN 16 REACTIONS; CHARGED-PARTICLE REACTIONS; DATA; DISTRIBUTION; INELASTIC SCATTERING; INFORMATION; INTERACTIONS; LEPTON-BARYON INTERACTIONS; LEPTON-HADRON INTERACTIONS; LEPTON-NUCLEON INTERACTIONS; NUCLEAR FRAGMENTS; NUCLEAR REACTIONS; NUMERICAL DATA; PARTICLE INTERACTIONS; SCATTERING; SPATIAL DISTRIBUTION; TARGETS 651820* -- Nuclear Properties & Reactions, A=150-189, Experimental; 651920 -- Nuclear Properties & Reactions, A=190-219, Experimental; 652020 -- Nuclear Properties & Reactions, A=220 & above, Experimental

Citation Formats

Back, B.B. Experimental studies of quasi-fission reactions. United States: N. p., 1988. Web.
Back, B.B. Experimental studies of quasi-fission reactions. United States.
Back, B.B. Fri . "Experimental studies of quasi-fission reactions". United States. doi:. https://www.osti.gov/servlets/purl/6573147.
@article{osti_6573147,
title = {Experimental studies of quasi-fission reactions},
author = {Back, B.B.},
abstractNote = {A large number of recent experimental studies have shown that a substantial fraction of the total reaction cross section in heavy-ion reactions is found in fission-like processes, which do not result from the fission decay of a completely fused system. Following the suggestion of Swiatecki such processes, which represents a complete relaxation of the relative kinetic energy and a substantial amount of net mass transfer between the two fragments, are denoted quasi-fission reactions. They are distinct from compound fission reactions by bypassing the stage of a completely fused-system. This typically means that they are associated with short reaction times, which results in several measurable characteristics such as broken forward-backward symmetries, large anisotropies of the angular distributions and increased widths of the fragment mass distributions. The distinction between quasi-fission and deep inelastic reactions is less stringent and has the character of a gradual evolution from one reaction type to the other, as found also as quasi-elastic reaction evolves into deeply inelastic processes as a function of the total kinetic energy loss. In the present paper some of the experimental data characterizing quasi-fission reactions are reviewed and discussed. 22 refs., 6 figs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Jan 01 00:00:00 EST 1988},
month = {Fri Jan 01 00:00:00 EST 1988}
}

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  • A large body of experimental data on these fission-like processes have become available in recent years using a number of different target-projectile combinations. None of these experimental studies are specifically addressing the question of entrance channel effects. These effects are expected to play an important role if the dynamics in the approach phase of the reaction is responsible for the occurrence of quasi-fission. An alternate interpretation in terms of the disappearance of the fission barrier at large partial waves, which is entirely a property of the completely fused system independent of the formation process, has also been proposed. In ordermore » to address these questions we have studied the system /sup 214/Th via three different entrance channels, namely /sup 32/S/plus//sup 182/W, /sup 48/Ti/plus//sup 166/Er and /sup 60/Ni/plus//sup 154/Sm. The analysis of the /sup 48/Ti/plus//sup 166/Er data is, as yet, incomplete and we shall therefore report only on the results of the /sup 32/S/plus//sup 182/W and /sup 60/Ni/plus//sup 154/Sm reactions in this paper. 4 refs., 3 figs.« less
  • Quantitative analyses of angular distributions and angle-mass correlations have been applied to the U + Ca reaction to obtain upper limit estimates for the cross sections for complete fusion near or below the interaction barrier. Extrapolating to the systems Ca + Cm and Ca + Es using the well established scaling properties of the extra push model, an estimate of the cross sections relevant to the efforts of synthesizing super-heavy elements in the region Z = 116 and N = 184 via heavy-ion fusion reactions are obtained. A simple evaporation calculation using properties of the super heavy elements shows thatmore » the failure to observe super-heavy elements with the Ca + Cm reaction is consistent with estimates of the complete fusion process. 33 refs., 9 figs., 1 tab.« less
  • Astrophysical r-process calculations of transbismuth elements are of interest because certain actinide pairs can be treated as chronometers in determining the duration of nucleosynthesis. For one such calculation where a particularly long galactic age was derived, 21 + 2 - 4 Gyr, we present evidence that the effect of beta-delayed fission appears to be seriously overestimated in uranium decay chains with A = 252 to 257. With this conclusion, it follows that this estimate of the galactic age must be considered more uncertain than if the calculated rates of beta-delayed fission were found to be acceptable. The nuclear level structuremore » of 238Np has been investigated using the 237Np(n,..gamma..)238Np reaction and the alpha decay of 242mAm as experimental probes. Having established a level scheme for 238Np that includes 47 excited levels and 93 secondary transitions, we find a high degree of correspondence between the experimental band structure and that of a semi-empirical model developed to predict excitations in odd-odd deformed nuclei. 35 refs., 4 figs., 3 tabs.« less