Program - Brookhaven National Laboratory

egime. These measurements are particularly challenging on fissile isotopes as the fission γ spectrum does
not present unique features which can be used to discriminate fission γ-rays from neutron capture. The
Los Alamos Neutron Science Center (LANSCE) provides a high intensity neutron flux from thermal to
several hundred keV. Coupled to this intense neutron source, the Detector for Advanced Neutron Capture
Experiments (DANCE) provides a highly segmented 4π measurement of the γ-ray energy and multiplicity
distributions. Finally, a specially designed Parallel Plate Avalanche Counter (PPAC) detected coincidence
fission fragments. Together, these instruments were used to provide a new high fidelity measurement of
neutron capture on 239 Pu. Existing measurements extend up to 10 keV incident neutron energy, while
measurements planned for Fall of 2012 will push the measurement up to several hundred keV. The simultaneous
measurement of (n,γ) and (n,f) events resulting from a single sample allowed the (n,γ) cross section
to be measured as a ratio to fission with reduced systematic uncertainty. Similar techniques applied to 235 U
resulted in an uncertainty of 3% at 10 keV. Results from the current analysis on 239 Pu will be presented.
PA 4 4:40 PM
High-precision measurement of the 238 U(n,γ) cross section with the Total Absorption
Calorimeter (TAC) at nTOF, CERN
Toby Wright, Jon Billowes, Tim Ware, University of Manchester (UK). Carlos Guerrero, the n TOF
Collaboration, CERN, Switzerland. Daniel Cano Ott, CIEMAT, Spain. Frank Gunsing, C. Lampoudis,
E. Berthoumieux, CEA, France. Cristian Massimi, Federica Mingrone, Universita di Bologna, Italy.
The uncertainty in the neutron capture cross section of 238 U introduces limitations in the simulation
of present, Gen III+ LWRs and Gen IV fast reactors. Sizable inconsistencies in this cross section still
appear in the epithermal energy region up to 25 keV, as is summarized on the NEA High Priority Request
List of measurements. In this context, the Accurate Nuclear Data for nuclear Energy Sustainability
(ANDES) project from the European Commission 7th Framework Programme aims, among others, to
achieve the required precision and improve the measurements of the 238 U cross section data. This neutron
capture cross section has been measured at the n TOF facility at CERN with two different detector setups,
and also measurements have been performed at GELINA at IRMM, with the aim of reducing the
uncertainty in the cross section down to 2%, leading to the most accurate 238 U neutron capture cross
section to date. This contribution focuses specifically on the time-of-flight measurement carried out with
the Total Absorption Calorimeter (TAC) at the CERN neutron-spallation source n TOF. The TAC is an
array of 40 BaF2 scintillators and has a large solid angle coverage, high γ-ray total absorption efficiency,
reasonable energy resolution, high segmentation and fast time response. The preliminary results in the
energy range between 0.3 eV and 100 keV will be presented. These include the corrections associated to
the background subtraction, normalization, detection efficiency and pile-up effects. A comparison with the
existing evaluated cross sections and previous measurements will also be presented.
PA 5 5:00 PM
Results on the 236 U Neutron Cross Section from the n TOF Facility
M. Barbagallo, for the n TOF collaboration
Istituto Nazionale di Fisica Nucleare, sez. Bari, Italy
One of the main goals of the n TOF experimental program is to measure with high resolution and high
accuracy neutron-induced reaction cross sections of interest for advanced nuclear technologies. In this
respect, capture and fission cross sections have been measured at n TOF for various U and Pu isotopes,
219