First experiment on fission transients in highly fissile spherical nuclei produced by fragmentation of radioactive beams.

Gesellschaft fuer Schwerionenforschung, 64291 Darmstadt, Germany.
Physical Review Letters (Impact Factor: 7.73). 08/2007; 99(4):042701. DOI: 10.1103/PhysRevLett.99.042701
Source: arXiv

ABSTRACT We report on a novel experimental approach for studying the dissipative spreading of collective motion in a metastable nuclear system, using, for the first time, highly fissile nuclei with spherical shape. This was achieved by fragmentation of 45 radioactive heavy-ion beams at GSI, Darmstadt. The use of inverse kinematics and a dedicated experimental setup allowed for the identification in atomic number of both fission fragments. From the width of their nuclear-charge distributions, a transient time of (3.3+/-0.7)x10(-21) s is deduced for initially spherical nuclei.

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    ABSTRACT: We investigate the importance of accounting for the transient time within the framework of the statistical approach (SA) for describing the fission process beginning from the quasistationary nuclear configuration. Two arguments are given in favor of the positive point of view on this problem. First, the average scission time is shown to be always larger than the inverse quasistationary fission rate by the value that is close to the transient time τr. Second, comparing the SA and the combined dynamical statistical approach (CDSA), we have found that suppressing the fission process for some delay time in the framework of the SA significantly reduces the amount of disagreement between the values of proper observables calculated using the SA and the CDSA.
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    ABSTRACT: The use of radioactive beams in inverse kinematics dramatically increased the number of isotopes which can be studied at excitation energies ranging from a few to several hundred MeV. Since this method is not subject to target restrictions, long isotopic and isotonic chains could be investigated, and hence, studies of the evolution of fission fragment charge yields, of total kinetic energies, as well as of the time scale of nuclear fission of highly excited compound nuclei with proton and neutron number of the fissioning nucleus, are possible.
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    ABSTRACT: An innovative approach for studying transient effects in nuclear fission is proposed. Fragmentation of radioactive actinides is employed to prepare fissile nuclei in well-defined initial conditions, and the fission-fragment nuclear charge distribution is used to establish a clock for the dynamical evolution of the system. Based on a so-far un-reached large number of fissioning systems, the study demonstrates the undeniable manifestation of transient effects at high excitation energy and addresses the question about the influence of initial deformation.

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