Target Characterization of Large Area Minor Actinide Layers for Fast Neutron Induced Fission Cross Section Experiments at nELBE


Target Characterization of Large Area Minor Actinide Layers for Fast Neutron Induced Fission Cross Section Experiments at nELBE

Kögler, T.; Beyer, R.; Eberhardt, K.; Hannaske, R.; Junghans, A. R.; Massarczyk, R.; Schwengner, R.; Vascon, A.; Wagner, A.

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 242Pu 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-of-flight 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 µg/cm2; total mass: 200 mg of 235U and 75 mg of 242Pu). 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, www.hzdr.de/trakula) supported by the Federal Ministry for Education and Research of Germany.
References

[1] OECD/NEA, „Nuclear Data High Priority Request List,“ 2011. [Online]. Available: 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 Assesment for Innovative Systems Using Recent Covariance Data Evaluations,“ 2008. [Online]. Available: http://www.nea.fr/html/science/wpec/volume26/volume26.pdf.

Keywords: fast neutron induced fission; target characterization

  • Poster
    International Conference on Nuclear Data for Science & Technology 2013, 04.-08.03.2013, New York, USA
  • Nuclear Data Sheets 119(2014), 404-406
    DOI: 10.1016/j.nds.2014.08.113

Permalink: https://www.hzdr.de/publications/Publ-18228
Publ.-Id: 18228