Abstract
Monte Carlo neutron transport codes such as MCNP rely on accurate data for nuclear physics cross-sections to produce accurate
results. At low energy, this takes the form of scattering laws based on the dynamic structure factor, S (Q, E). High density polyethylene
(HDPE) is frequently employed as a neutron moderator at both high and low temperatures, however the only cross-sections
available are for T =300 K, and the evaluation has not been updated in quite some time. In this paper we describe inelastic neutron
scattering measurements on HDPE at 5 and 300 K which are used to improve the scattering law for HDPE. We describe the experimental
methods, review some of the past HDPE scattering laws, and compare computations using these models to the measured
S (Q, E). The total cross-section is compared to available data, and the treatment of the carbon secondary scatterer as a free gas is
assessed. We also discuss the use of the measurement itself as a scattering law via the 1 phonon approximation. We show that a
scattering law computed using a more detailed model for the Generalized Density of States (GDOS) compares more favorably to
this experiment, suggesting that inelastic neutron scattering can play an important role in both the development and validation of
new scattering laws for Monte Carlo work.
