Program - Brookhaven National Laboratory

RA 3 11:20 AM
A Microscopic Theory of Fission for Nuclear Data Needs
W. Younes, N. Schunck, D. Gogny
Lawrence Livermore National Laboratory
Since the official discovery of fission 75 years ago, understanding this phenomenon remains a daunting
challenge in nuclear physics. At the same time, a more fundamental understanding of fission is essential
to a variety of societal applications as well as to the description of natural phenomena ranging from the
heating of the earth’s interior to the production of heavy elements in astrophysical environments. With
the advent of modern parallel computers and powerful theoretical methods, fission calculations within a
consistent microscopic framework built from protons, neutrons and an effective interaction between them
are beginning to produce useful nuclear data. We will present microscopic calculations of fission-fragment
properties (kinetic and excitation energies, yields etc.) and compare them to experimental data. We will
also discuss the prospects for a microscopic theory of fission for data evaluations wherever the experimental
data are sparse, ambiguous, or impossible to measure. This work performed under the auspices of the U.S.
Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
RA 4 11:40 AM
Investigating the Dynamics of Fission at High Excitation Energy in Reactions Induced by
Relativistic Protons and Deuterons on Lead
Y. Ayyad, J. Benlliure*, E. Casarejos, M. Fernandez, T. Kurtukian, D. Pérez, Universidade de Santiago
de Compostela, 15782 Santiago de Compostela, Spain. A. Bacquias, L. Giot, V. Henzl, D. Henzlova, A.
Kelic, S. Lukic, P. Nadtochy, R. Pleskac, M.V. Ricciardi, K.-H. Schmidt, C. Schmitt, GSI
Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany. A. Boudard, S. Leray,
DSM/IRFU/SPhN, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France. T. Enqvist, Oulu Suthern
Institute and Department of Physics, University of Oulu, Finland. F. Farget, GANIL, BP 55027 F-14076
Caen Cedex, France.
Several observables such us total fission cross sections, pre-saddle neutron and gamma emission or the
measurement of the fission time using crystal blocking techniques show clear indications for a delay of fission
at high excitation energies when compared to other de-excitation channels, namely particle evaporation
[1]. This delay is explained as the manifestation of transient effects produced by the coupling between
intrinsic and collective degrees of freedom in fission [2]. This coupling can be macroscopically understood
as a dissipative process. Moreover, the investigation of proton induced fission on lead is relevant for the
radiological characterization of spallation targets. In this work we will present measurements of total fission
cross sections and charge distributions of the fission fragments produced in proton and deuteron on lead
reactions at relativistic energies. The experiment was performed in inverse kinematics at GSI Darmstadt.
Beams of lead ions were accelerated by the SIS18 synchrotron at 500 A MeV impinging then onto a liquid
hydrogen/deuterium target. Projectile reaction residues, in particular fission fragments flying forward,
were identified using a set of plastic scintillators and ionization chambers. Measured data were used to
benchmark model calculations describing residual nuclei production in spallation reactions. In particular
we used several model calculations to prove the sensitivity of the width of the charge distributions of the
fission fragments to the temperature reached by the fissioning system at saddle. The deduced temperatures
are clearly influenced by transient effects which cool down the fissioning nuclei from ground to saddle.
Corresponding author: J. Benlliure
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