Program - Brookhaven National Laboratory

as well as for a variety of Minor Actinides. As part of this extensive program, the capture cross section
of 236 U has been recently measured. Together with the fission data previously obtained at n TOF, these
cross sections are of interest for the development of the Th/U fuel cycle for energy production, as well as
for studies of advanced reactor technology for nuclear wastes incineration. In order to minimize systematic
uncertainties, the capture cross section was measured with two detection systems: a pair of low neutron
sensitivity C6D6 detectors and a BaF2 Total Absorption Calorimeter. The suitable features of the facility,
in particular the high instantaneous flux and high resolution of the neutron beam, in combination with
the high performance detection systems have allowed us to determine the cross section and the associated
resonance parameters with an accuracy better than the required value of 10%. The results of the
measurements will here be presented, in comparison with (scarce) previous data and current evaluations.
PA 6 5:15 PM
Study of Neutron-Induced Fission Resonances in 234 U Measured at the CERN n TOF
Facility
E. Leal-Cidoncha, I. Durán, C. Paradela, D. Tarrío
Universidade de Santiago de Compostela (Spain)
L. Audouin, L. S. Leong, L. Tassan-Got
CNRS/IN2P3-IPN Orsay (France)
and the n TOF Collaboration
(CERN)
We present the resolved resonance region analysis of the high resolution 234 U(n,f) cross section data obtained
using a reaction chamber based on parallel-plate avalanche counters (PPACs) at the CERN Neutron
Time-of-Flight n TOF facility extending the work performed at reference [1]. Current evaluations [2], [3]
are based on G. D. James et al. data obtained in the 70’s decade [4]. Hence, this study will allow us to
improve the knowledge of the 234 U fission cross section in the resolved resonance region of interest for reactor
studies in the thorium fuel cycle. The resonance parameters in the energy range from 1 eV to 1500 eV,
corresponding to the resolved resonance region (RRR) have been studied with the Multilevel Multichannel
R-matrix code (SAMMY) [5] using the Multilevel Breit-Wigner approximation of the R-matrix. Corrections
of Doppler broadening due to the thermal motion of the nuclei in the sample, resolution broadening
of the neutron beam, self-shielding, multiple scattering, normalization and background were included in
the SAMMY analysis. The resonance parameters in the JENDL 3.3 evaluation, which were adopted from
reference [4] after modification of an average radiative width to 0.026 eV, were used as initial parameters
to make the fit. In addition, the statistical analysis has been accomplished with the SAMDIST code [6] in
order to study the level spacing, the reduced fission width and the Mehta-Dyson correlation.
[1] C. Paradela et al. Physical Review C 82. 034601 (2010). [2] K. Shibata et al. , J. Nucl. Sci. Technol.
39, 1125 (2002). [3] M.B. Chadwick et al., Nucl. Data Sheets 107, 2931 (2006). [4] G.D. James et al: Phy.
Rev., C15, 2083 (1977). [5] Larson N. M., Oak Ridge National Laboratory, USA, 2007. [6] Leal L. C. and
Larson N. M., Oak Ridge National Laboratory, USA, 1995.
PA 7 5:30 PM
New Measurement of the 25 Mg(n, γ) Reaction Cross Section
C. Massimi, for the n TOF collaboration
Dipartimento di Fisica, Università di Bologna, and Sezione INFN di Bologna, Bologna, Italy
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