Program - Brookhaven National Laboratory

Target Characterization of Large Area Minor Actinide Layers for Fast Neutron Induced
Fission Cross Section Experiments at nELBE
T. Kögler, R. Hannaske, R. Massarczyk, Helmholtz-Zentrum Dresden-Rossendorf, Postfach 510 119,
01324 Dresden, Germany, Technische Universität Dresden, Postfach 100 920, 01076 Dresden, Germany.
R. Beyer, Z. Elekes, A.R. Junghans, R. Schwengner, A. Wagner, Helmholtz-Zentrum Dresden-Rossendorf,
Postfach 510 119, 01324 Dresden, Germany. K. Eberhardt, A. Vascon, Johannes Gutenberg Universität
Mainz, 55099 Mainz, Germany.
The development of Accelerator Driven Systems (ADS) requires accurate nuclear data. Especially neutron
induced fission cross sections of Plutonium and minor actinides in part show high uncertainties in the fast
energy range. For 242 Pu current uncertainties are of around 21 %, the target uncertainties in the order of
7 %. Sensitivity studies ([1], [2]) show that the total uncertainty has to be reduced below 5 %, to enable
reliable neutron physical simulations. This challenging task will be performed at the neutron time-offlight
facility of the new German National Center for High Power Radiation Sources at HZDR, Dresden.
Improved experimental conditions (low scattering environment) and beam power, paired with the right
spectral shape of the nELBE neutron source will provide excellent conditions to achieve this aim. A parallel
plate ionization chamber with it’s approximately 100 % intrinsic detection efficiency will measure fission
fragments from thin minor actinide layers (areal density: 580 and 220 microgram per centimeter 2 ; total
mass: 200 milligram of 235 U and 75 milligram of 242 Pu). These very homogeneous targets are produced
by the institute of radiochemistry of the University of Mainz. To handle the high specific alpha activity
of the Pu targets, a combination of fast preamplifiers and digital signal processing has been developed to
suppress pile-up effects. It is planned to determine the homogeneity of the minor actinide targets by two
different methods. Due to their high specific activity the number of fissionable Pu atoms per unit area will
be determined by a spatially resolved alpha spectroscopy. The required setup was optimized using Geant
4 simulations. Results of this simulations and first experimental approaches will be presented. For the
uranium targets it is planned to determine the homogeneity in a fission chamber with a collimated neutron
beam at PTB Braunschweig. Physical properties (distance between anodes and cathodes, counting gas
etc.) of the chamber have also been optimized using the Geant 4 framework. The work is embedded in the
TRAKULA project (BMBF 02NUK13A) supported by the Federal Ministry for Education and Research
of Germany.
[1] OECD/NEA, Nuclear Data High Priority Request List, (2011), http://www.nea.fr/html/dbdata/hprl/
[2] Working Party on International Evaluation Co-operation of the NEA Nuclear Science Committee, Uncertainty
and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations,
(2008), http://www.nea.fr/html/science/wpec/volume26/volume26.pdf
PR 69
Monte Carlo Simulation of Prompt Fission Neutron Observables for the Spontaneous
Fission of 236 Pu, 238 Pu,
O. Serot , O. Litaize, C. Manailescu, D. Regnier, CEA, DEN-Cadarache, F-13108
Saint-Paul-lez-Durance, France.
Recently, a Monte Carlo code which simulates the fission fragment deexcitation process has been developed
at CEA-Cadarache. Our aim is to get a tool capable to predict spectra and multiplicities of prompt particles
and to investigate possible correlations between fission observables. One of the main challenges is to define
properly the share of the available excitation energy at scission between the two nascent fission fragments.
In a previous work [1], these excitation energies were treated within a Fermi-gas approximation in aT 2
(where a and T stand for the level density parameter and the nuclear temperature) and a mass dependent
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