Program - Brookhaven National Laboratory

mock-up WWER-1000 reactor at LR-0 research reactor in Rez. The measurement places were positioned
(among other points) on the inner surface of the reactor pressure vessel (RPV), in the 1/4 thickness of the
RPV and at the RPV back side. RPV model was represented by the Iron slab of the 20 cm thickness. The
proton recoil method was used for neutron spectra measurement. The adequate MCNP neutron spectra
calculations (C) based on different data libraries (ENDF/B-VII.1, JEFF-3.1.2, BROND-3, JENDL-4.0,
CENDL-3.1 and TENDL-2011) have been done for most of the above mentioned Iron assemblies and compared
with measurements (M). The analysis of C/M values is focused to neutron energy interval 0.06 - 1.3
MeV. Some repeated differences between measurements and calculations using different data libraries are
observed in various experimental assemblies.
Session KF Neutron Cross Section Measurements
Wednesday March 6, 2013
Room: Central Park East at 1:30 PM
KF 1 1:30 PM
Neutron-Induced Reactions on U and Th - New Cross-Section Measurements via AMS
A. Wallner, VERA Laboratory, Faculty of Physics, University of Vienna, Währinger Strasse 17, A-1090,
Austria and. R. Capote Noy, NAPC Nuclear Data Section, International Atomic Energy Agency, A-1400
Vienna, Austria. M. Christl, Dept. of Physics, Laboratory of Ion Beam Physics, ETH Zurich, Zurich,
Switzerland. L.K. Fifield, M. Srncik, S. Tims, Department of Nuclear Physics, Australian National
University, Canberra, ACT 0200, Australia. F. Käppeler, Karlsruhe Institute of Technology (KIT),
Campus Nord, Institut für Kernphysik, Karlsruhe, Germany. A. Krasa, A. Plompen, European
Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel, Belgium.
J. Lippold, Ruprecht-Karls-Universität Heidelberg, Institut für Umweltphysik, Im Neuenheimer Feld 229,
69120 Heidelberg, Germany. P. Steier, S. Winkler, VERA Laboratory, Faculty of Physics, University of
Vienna, Währinger Strasse 17, A-1090, Austria.
Existing data for neutron-induced reactions on U and Th have been measured via detection of the prompt
radiation, by the activation technique and by detection of emitted particles. A major difficulty in these
experiments is the discrimination against the strong γ-background (e.g. from the competing fission channel)
or unfavourable decay schemes. Up to now, no measurements have been performed for such reactions
applying accelerator mass spectrometry (AMS) except recent work at the VERA (Vienna Environmental
Research Accelerator) laboratory. Recent studies exhibit some discrepancies at keV and MeV energies
between major nuclear data libraries for 238 U(n,γ), 232 Th(n,γ) but also for (n,xn) reactions. A similar
difference for the cross section ratio 238 U(n,γ)/ 197 Au(n,γ) was found between data based on TOF and
prompt γ-detection. Some of those ratio measurements may be biased because of the difficulties in detecting
all the gamma rays emitted by the 238 U(n,γ) and 197 Au(n,γ) reactions. Our method based on direct atomcounting
has the advantage that the involved systematic uncertainties are in no way correlated with the
uncertainties inherent e.g. to the TOF technique. Therefore, such data provide important and independent
information for key reactions of reactor physics. We have extended our previous (n,γ) measurements on
235,238 U using AMS to higher neutron energies and to additional reaction channels. Natural uranium
and thorium samples were exposed to neutrons of energies between 0.5 and 23 MeV at IRMM. After the
activation, the production of longer-lived nuclides was quantified by AMS. The radionuclides counted via
AMS were either the direct product of a reaction or a decay-product of a directly produced short-lived
nuclide. A particular feature of the U and Th isotopes are the low (n,2n) and (n,3n) thresholds; even the
232 Th(n,4n) reaction could be studied. We will present new data for 232 Th(n,γ), 232 Th(n,2n), 232 Th(n,4n)
and 232 Th(n,α), as well as for 238 U(n,γ) and 238 U(n,3n).
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