Program - Brookhaven National Laboratory

An Evaluation of the Scattering Law For Light and Heavy Water in ENDF-6 Format,
Based on Experimental Data and Molecular Dynamics
J.I. Marquez Damian, J.R. Granada
Fisica de Neutrones, Centro Atomico Bariloche, Conicet/CNEA, Argentina
D.C. Malaspina
Computation, Modeling & Bioinformatics Center, Chemistry of Life Process Institute, Northwestern
University, USA
There exist only two evaluations of the scattering law for light and heavy water available in ENDF format
[1,2]. Both evaluations are based on experimental data measured by Haywood in the 60’s, and use a free
gas model to represent the translational motion of the molecules. These evaluations are acceptable for
reactor applications, but show significant discrepancies with total cross section measurements in the subthermal
range and with angular distributions of the differential cross, caused by the simplified structure and
dynamics used in these models. In this work we present an evaluation in ENDF-6 format of the scattering
law for light and heavy water computed using the LEAPR module of NJOY99 [1]. The models used in
this evaluation are based on experimental data on light water dynamics measured by Novikov [3], partial
structure factors obtained by Soper [4], and molecular dynamics calculations performed with GROMACS
[5] using a reparameterized version of the flexible SPC model by Toukan and Rahman [6]. The models use
the Egelstaff-Schofield diffusion equation for translational motion, and a continuous spectrum calculated
from the velocity autocorrelation function computed with GROMACS. The scattering law for H in H2O is
computed using the incoherent approximation, and the scattering law D and O in D2O are computed using
the Sköld approximation for coherent scattering. The calculations show a significant improvement over
ENDF/B VI and ENDF/B VII when compared with measurements of the total cross section, differential
scattering experiments and quasi-elastic neutron scattering experiments (QENS).
[1] R.E. MacFarlane. “New thermal neutron scattering files for ENDF/B-VI release 2.” LA-12639-MS.
Technical report, Los Alamos National Laboratory, 1994. [2] M. Mattes and J. Keinert. “Thermal neutron
scattering data for the moderator materials H2O, D2O and ZrHx in ENDF-6 format and as ACE library
for MCNP (X) codes.’ INDC (NDS)-0470. Technical report, IAEA, 2005. [3] A.G. Novikov, A.A. Vankov,
and L.S. Gosteva. “Temperature dependence of the general spectrum for water.” Journal of Structural
Chemistry, 31(1):77-85, 1990. [4] A.K. Soper and C.J. Benmore. “Quantum differences between heavy
and light water.” Physical review letters, 101(6):65502, 2008. [5] D. van der Spoel, E. Lindahl, B. Hess,
G. Groenhof, A. E. Mark, H. J. C. Berendsen, “GROMACS: Fast, Flexible and Free.” J. Comp. Chem.
26:1701-1718, 2005. [6] K. Toukan, A. Rahman, “Molecular-dynamics study of atomic motions in water.”
Physical Review B 1985, 31, 2643-2648.
LE 8 5:45 PM
The Production and Performance of JEFF3.1.2 Nuclear Data Libraries in ANSWERS
Codes
R. J. Perry, R. P. Hiles
AMEC, Kimmeridge House, Dorset Green Technology Park, Winfrith Newburgh, Dorchester, Dorset,
DT2 8ZB, UK
The JEFF3.1 evaluated nuclear data library was released in 2005 and represented the culmination many
years of measurement and evaluation. As a result of some issues identified by the validation of the JEFF3.1
library, a small number of nuclides were re-evaluated to improve results and were released as JEFF3.1.1, in
2009. The latest version of the JEFF library, JEFF3.1.2, was released in January 2012. This incorporated
new evaluations of the hafnium resolved resonance range and the inclusion of gamma production data
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