Program - Brookhaven National Laboratory

Neutron elastic scattering, radiative capture and fission cross section covariances for Np-237 are evaluated
in the resolved resonance region. Analytical expressions describing the sensitivities of cross sections with
respect to the resonance parameters at certain energy point are derived from the Multi-level Breit-Wigner
formula. Then they are numerically integrated to obtain the sensitivities of average cross sections to
the resonance parameters in an arbitrary energy bin. The full covariance matrix is constructed with a
thermal region based directly on experimental data, and a resonance region using the resonance parameter
uncertainties from Atlas of Neutron Resonances. Scattering radius uncertainty is handled explicitly, and
by using ENDF file 33 we bypass the possible file 32 processing issue which may lead to discrepancies
between the multigroup covariances by the different processing codes.
PR 77
D-T Fusion Neutron Irradiations at AWE
Matt Gardner, Andrew Simons, Ben Williams, Mike Rubery, AWE.
A team at AWE has conducted a 2-year feasibility study to determine the suitability of ASP, its 300 keV
deuteron accelerator, for the measurement of neutron-induced reaction cross-sections. Decay gammas resulting
from 89Y(n,n’)89mY and 89Y(n,2n)88Y reactions have been collected using high-purity germanium
and various different irradiation and counting geometries. Modelling of the ASP system and D-T interaction
has been carried out using Geant4 in order to determine neutron spectra as a function of source-target
angle and distance. Data collected using both analogue and list-mode systems have been analysed via
parallel routes and the results compared. Fast extraction for short-lived products and low-background
counting for long-lived products have both been employed; results from the data so collected are presented
here.
Corresponding author: Mark Cornock
PR 78
Commara-3.0 Covariance Library
S. Hoblit, M. Herman, S. Mughabghab, A. Sonzogni, Brookhaven National Laboratory. G. Palmiotti, M.
Salvatores, Argonne National Laboratory. P. Talou, M. Rising, M.B. Chadwick, G.M. Hale, A.C. Kahler,
T. Kawano, R.C. Little, P.G. Young, Los Alamos National Laboratory.
The Commara library is a set of covariances for the major reaction channels that are of importance to
thermal and fast breeder reactors in addition to sensitivity studies. Version 3.0 will build upon the earlier
work of version 2.0, released in March, 2011, which contained covariances for 110 materials in the AFCI
33-group energy structure. The new version will refer to the central values of ENDF/B-VII.1, released
December, 2011, and will incorporate covariances included in this release of the ENDF library, increasing
the number of materials in Commara 3.0 to approximately 190. In addition to covariances for the 4-
5 major reaction channels, version 3.0 will also expand the number of materials with covariances for
prompt fission neutron spectra, mubar (P1 elastic) and nubar (average number of neutrons/fission), where
available. Covariances for cross-reaction channels present in ENDF/B-VII.1 will also be included. The
energy weighting will be modified from the pure 1/E weighting used with Commara 2.0 to 1/E + fission
spectrum.
PR 79
301