Program - Brookhaven National Laboratory

experimental data and for the production of these covariances. In addition, for the first time, sensitivities
of the Prompt Fission Neutron Spectra (PFNS), the nu-bar, and mu-bar (elastic), along with the respective
covariances, were consistently incorporated into EMPIRE and into the assimilation procedure. These
along with the sensitivities of the cross sections to perturbation of model parameters were used to perform
actual assimilation (reported in a separate contribution). These results should shed some light on the issue
of the shape of PFNS, which is not well known experimentally, as well as on cross-correlations among cross
sections, PFNS, nu-bars and possibly also mu-bars. Details of the EMPIRE calculations, including choice
of reaction models and experimental data will be discussed.
[1] M. Herman, R. Capote, P. Oblozinsky, M. Sin, A. Trkov, H. Weinke, and V. Zerkin, Nuclear Data Sheets
108 (2007) 2655-2715. [2] R. Capote, M. Herman, P. Oblozinsky, et al., Nucl. Data Sheets 110(2009) 3107-
3214. Database available online at http://www-nds.iaea.org/RIPL-3/.
PR 83
The Angular Distribution of Neutrons Scattered from Deuterium below 1 Mev
A. Plompen, S. Kopecky, N. Nankov, EC-JRC-IRMM, Geel, Belgium. K. Kozier, D. Roubtsov, R. Rao,
D. Watts, AECL-CRL, Chalk River, Canada. R. Beyer, E. Grosse, R. Hannaske, A. Junghans, M.
Massarczyk, R. Schwengner, D. Yakorev, A. Wagner, HZDR Rossendorf, Germany. M. Stanoiu,
IFIN-HH, Bucharest-Magurele, Romania. L. Canton, INFN, Padova, Italy. R. Nolte, S. Röttger, PTB,
Braunschweig, Germany. J. Svenne, U. Manitoba, Winnipeg, Canada.
A re-evaluation of the angular distribution of elastic scattering of neutrons off deuterium at energies below
1 MeV is one of the high priority requests featured on the High Priority Request List for nuclear data
maintained by the OECD-NEA. The request is due to changes in C/E for the effective multiplication
factor k and, more importantly, for the coolant void reactivity in heavy water critical benchmarks. These
changes came about through the change from ENDF/B-VI.4 to ENDF/B-VI.5 in the angular distribution
of n+d scattering. This request has led to several efforts to pin-down the angular distribution with nuclear
theory model calculations, but the point is still open and accurate measurements are required to arbitrate
between different evaluations and model calculations. On the other hand, measurements of this angular
distribution are scarce and discrepant, and the few that are reported in the literature date from the fifties
and sixties. Neutron elastic scattering measurements were made at the nELBE neutron time-of-flight
facility at a 6 m flight path. Energies below 1 MeV were studied using a setup consisting of eight 6 Li-glass
detectors placed at nominal angles of 15 and 165 degrees with respect to the incident neutron beam. These
angles were chosen since an earlier study showed that the ratio of the scattered neutron currents at theses
angles has a large sensitivity to differences between the various data evaluations for deuterium, while still
allowing a practical experimental setup. A polyethylene (CD2) sample enriched to 99.999% in deuterium
was used. In the experimental data analysis contributions from time-uncorrelated room-return and timecorrelated
air-scatter are subtracted using the time-of-flight spectrum and the sample-out measurements,
respectively. Monte Carlo calculations are needed to correct for the carbon contribution, sample multiple
scattering, air scatter and the energy dependence of the detection efficiency. The high repetition rate
and shorter flight path of the nELBE experiment offer clear advantages compared with a similar attempt
with the same setup at GELINA at a long flight path (300m). Accurate 165/15 degree angle signal ratios
were obtained that will be compared with the various proposed angular distributions. Simultaneously, the
early-day experiments using a proportional counter to infer angular distributions from deuterium-recoil
pulse-height distributions are being studied through a new experiment with such a device at PTB. The
status of this work will be presented and compared to the earlier work and the results of the nELBE
experiment.
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