Program - Brookhaven National Laboratory

CIEMAT
C. Guerrero and the n TOF collaboration
CERN
There is a great interest in performing new neutron cross section measurements of minor actinides for
reducing the sometimes unacceptably large uncertainties in the evaluated data. Such data are of great
importance for evaluating the design of advanced nuclear reactors and, in particular, for determining
their performance in the transmutation of the nuclear waste. The capture cross sections of 241 Am and
243 Am were measured at the n TOF facility at CERN with a BaF2 Total Absorption Calorimeter [1],
in the energy range from 1 eV up to a few keV. A preliminary analysis of the 241 Am and a complete
analysis of the 243 Am measurement, including the data reduction and the resonance analysis, will be
presented. For the case of the 243 Am, there are no capture data below 250 eV available in the EXFOR
database. There are three measurements reported [2,3], but their analysis results haven’t been published
yet. All the existing evaluations of the elastic and capture cross sections are based essentially in one
single transmission measurement by Simpson et al. [4]. Above 250 eV, there are only two incompatible
capture measurements available [5,6]. Such a lack of experimental data causes the significant differences
existing between the ENDF/B-VII.0, JEFF-3.1, and JENDL-4.0 evaluated data libraries. The measurement
performed at n TOF will contribute to the reduction of the uncertainty in the 243 Am (n, γ) cross section
in the resolved resonance region, and indicates that the capture cross section in the existing libraries is
underestimated in the energy range between 250 eV and 2 keV. The 241 Am is part of the experimental
program of the ANDES project, and preliminary results will be presented.
[1] C. Guerrero et al., Nucl. Instr. Methods A 608, 424 (2009). [2] M. Jandel et al., AIP Conf. Proc. 1090,
220 (2009). [3] J. Hori et al., JAEA-Conf 2009-004, 123-128 (2009). [4] O. D. Simpson et al., Nucl. Sci.
Eng. 55, 273 (1974). [5] L.W.Weston and J.H.Todd, Nucl.Sci.Eng. 91, 444 (1985). [6] K. Wisshak and G.
Käppeler, Nucl. Sci. Eng., 85, 251-260 (1983).
HA 7 5:30 PM
Fission Fragment Angular Distribution for Th-232(n,f) at the CERN n TOF Facility
D. Tarrío, I. Durán, C. Paradela
Universidade de Santiago de Compostela (Spain)
L. Audouin, L.-S. Leong, L. Tassan-Got
CNRS/IN2P3 - IPN Orsay (France)
The n TOF Collaboration
CERN-n TOF
In the development of new nuclear reactors, Th/U cycle is an alternative to the most widely used U/Pu
cycle, producing a smaller quantity of transuranic elements. A good knowledge of the involved reactions is
required and, in particular, the neutron-induced fission of Th-232, that plays an important role in this fuel
cycle. The n TOF facility at CERN is carrying out an extensive program on neutron-induced reactions.
The high-intensity neutron beam covers an unprecedented neutron energy range, from less than 1 eV up
to 1 GeV. In order to study fission reactions, a chamber with up to ten Parallel Plate Avalanche Counters
(PPAC) is used to identify, in time coincidence [1,2], both fission fragments emitted in the targets placed in
between. The stripped cathodes used in the PPAC allow us to know the fragment position in each detector
and, therefore, to determine their trajectory. However, in former experiments, the measured fission cross
sections had to be corrected by means of the limited geometrical acceptance affecting the detector efficiency,
being particularly important for neutron energies close to the multiple-chance thresholds. An improved
geometrical configuration where both detectors and targets are tilted 45 ◦ with respect to the neutron beam
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