Program - Brookhaven National Laboratory

PR 74
Resonance Analysis of the 233 U Capture Cross Section Measured at n TOF
C. Carrapiço, for the n TOF Collaboration, IST/ITN Instituto Superior Técnico, Uviversiade Técnica de
Lisboa.
The neutron capture and fission cross sections of the 233 U have been measured simultaneously at the neutron
time-of-flight facility n TOF at CERN in the energy range from 1 eV to 1 keV using a high performance
4π BaF2 Total Absorption Calorimeter (TAC). This is a very challenging task aiming at disentangling the
neutron capture signature from fission, the main competing reaction, whose cross-section is several times
higher than capture. The data analysis was performed using the Calorimetric Shape Decomposition (CSD)
method to separate the contributions to the total spectrum in the TAC, arising from neutron capture and
neutron induced fission reactions. The resonance analysis of 233 U was performed using the capture and
fission yields obtained under similar conditions, and an additional fission yield measured also n TOF but
with another fission detector. Besides a succinct description of the TOF spectrometer at CERN and
the detection capabilities of the TAC, results obtained for the resonance parameters are presented and
compared with nuclear data libraries.
PR 75
Measurement of 243 Am(p,tf) as a Surrogate for 240 Am(n,f)
R.J. Casperson, J.T. Burke, Lawrence Livermore National Laboratory, Livermore, California 94551,
USA. M. McCleskey, A. Saastamoinen, E. Simmons, A. Spiridon, Cyclotron Institute, Texas A & M
University, College Station, Texas 77843, USA. A. Ratkeiwicz, Department of Physics and Astronomy,
Rutgers University, New Brunswick, New Jersey 08903, USA. A. Blanc, CEA, Service de Physique
Nucleaire, BP 12, 91680 Bruyeres-le-Chatel, France. M. Kurokawa, RIKEN Nishina Center, Saitama
351-0198, Japan. R.G. Pizzone, Laboratori Nazionali del Sud-INFN, Catania, Italy.
The cross sections of (n,f) reactions are of interest in reactor modeling, but on short-lived isotopes, such
as 240 Am, can be very difficult to measure. To avoid the enormous background created by such short-lived
isotopes, we use the surrogate ratio method, which allows us to determine the ratio of an unknown cross
section relative to a known one. In the case of 240 Am(n,f), the ratio is relative to 235 U(n,f), and we use (p,t)
reactions to populate the relevant compound nuclei. We present preliminary results for measurements of
243 Am(p,tf) and 238 U(p,tf) using the STARLiTe detector system at the Texas A & M University Cyclotron
Institute. The performance of the recently commissioned data acquisition system will also be presented.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore
National Laboratory under Contract DE-AC52-07NA27344.
PR 76
Neutron Cross Section Covariances for Np-237 in the Resolved Resonance Region
Young-Sik Cho and Young-Ouk Lee, Nuclear Data Center, Korea Atomic Energy Research Institute,
Daejeon 305-353, Korea.
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