Program - Brookhaven National Laboratory

and time) of the probability distribution functions that describe the correlated time dependent locations
of the atoms. Previously, significant assumptions were used to allow the calculation of such correlation
functions and subsequently S(α,β) for various atomic systems. More recently, a predictive approach based
on ab initio quantum mechanics or classical molecular dynamics has been formulated to estimate S(α,β).
In principle, these modern atomistic simulation methods make it possible to generate the inelastic thermal
neutron scattering cross sections of any material and to accurately reflect the physical conditions of
the medium (i.e, temperature, pressure, etc.). In addition, the generated cross sections are free from assumptions
such as the incoherent approximation of scattering theory and, in the case of solids, crystalline
perfection. As a result, new and improved thermal neutron scattering data libraries have been generated
for a variety of materials. Among these are reactor moderators and reflectors such as reactor-grade graphite
and beryllium (with coherent inelastic scattering), beryllium carbide, silicon dioxide, cold and ultracold
neutron media such as solid methane and solid deuterium, and neutron beam filters such as sapphire and
bismuth. Consequently, it is anticipated that the above approach will play a major role in providing the
nuclear science and engineering community with its needs of thermal neutron scattering data especially
when considering new materials where experimental information may be scarce or nonexistent.
HC 5 5:00 PM
Level Density Options for Hauser-Feshbach Model Calculations from an Experimental
Point of View
A.V. Voinov, S.M. Grimes, C.R. Brune, T.N. Massey
Department of Physics and Astronomy, Ohio University, Athens Ohio 45701
The current generation of nuclear reaction codes uses many options for level density inputs which affect
cross section calculations to a large extent. Level density parameters determined on the basis of the neutron
resonance data obviously experience problems related to both unknown spin and parity distributions at
neutron resonance energies and way the level density is extrapolated towards the discrete level region.
Therefore, the extensive tests of available input level density options in modern reaction codes are needed.
Particle spectra from compound nuclear reactions are very sensitive to level densities of residual nuclei.
We have measured neutron, proton and alpha spectra from reactions induced by deuterons, 3 He, alpha
particles and 6,7 Li beams from the tandem accelerator of the Edwards Laboratory. It is seen that at beam
energies around 2-4 MeV/A spectra measured at backward angles do not significantly depend on the type
of incoming species indicating that the compound reaction mechanism is dominant. Experimental particle
spectra have been compared to calculations from the Empire nuclear reaction code [1] employing different
input options for the level density model. It is shown that calculations are sensitive to input level densities
and it is possible to rule out some of the models. Particularly, we found that for the mass range 50-60,
the level density model must include the constant temperature formula. The model based on Gilbert and
Cameron formulation [2] is the best to describe compound nuclear reactions in this mass range. Empire
calculations against experimental data are presented.
[1] M. Herman, R. Capote, B. Carlson, P. Oblozinsky, M. Sin, A.Trkov, H. Wienke and V. Zerkin, Nucl.
Data Sheets 108, (2007) 2655. [2] A. Gilbert, F. S.Chen and A. G. W. Cameron, Can. J. Phys 43, (1965)
1248.
HC 6 5:15 PM
Cross Section Calculation of Deuteron-Induced Reactions Using Extended CCONE Code
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