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International audience; Improvements in determination of the thermal scattering law of moderator materials (measuring, calculating and validating) are important for accurate prediction of neutron thermalization in nuclear systems. In this work a methodology for producing thermal scattering libraries from the experimental data for polyethylene C2H4 n is discussed. Double differential scattering cross section (DDSCS) experiments were performed at the Spallation Neutron Source of Oak Ridge National Laboratory (SNS ORNL). New scattering kernel evaluations, based on phonon spectrum for C2H4 n, are created using the NJOY2016 code. Two different methods were used direct and indirect geometry neutron scattering at ARCS and SEQUOIA, and VISION instruments, respectively, where the phonon spectrum was derived from the dynamical structure factor S(Q,ω) obtained from the measured DDSCS. In order to compare and validate the newly created library, the experimental setup was simulated using MCNP6.1. Compared with the current ENDF/B-VII.1, the resulting RPI C2H4 n libraries improved both double differential scattering and total scattering cross sections. A set of criticality benchmarks containing C2H4 n from HEU-MET-THERM resulted in an overall improved calculation of Keff, although the libraries should be tested against benchmarks more sensitive to C2H4 n. The DFT + oClimax method is used and is shown to be most comprehensive method for analysis of moderator materials. The importance of DFT + oClimax method lies in the fact that it can be validated against all data measured at VISION, ARCS and SEQUOIA, and experimental total scattering cross section measurements. © 2018 Elsevier Ltd

Nd2Hf2O7, belonging to the family of geometrically frustrated cubic rare earth pyrochlore oxides, was recently identified to order antiferromagnetically below TN 0.55 K with an all in all out arrangement of Nd3 moments, however, with a much reduced ordered state moment. Herein, we investigate the spin dynamics and crystal field states of Nd2Hf2O7 using muon spin relaxation muSR and inelastic neutron scattering INS measurements. Our muSR study confirms the long range magnetic ordering and shows evidence for coexisting persistent dynamic spin fluctuations deep inside the ordered state down to 42 mK. The INS data show the crystal electric field CEF excitations due to the transitions both within the ground state multiplet and to the first excited state multiplet. The INS data are analyzed by a model based on CEF and crystal field states are determined. Strong Ising type anisotropy is inferred from the ground state wave function. The CEF parameters indicate the CEF split Kramers doublet ground state of Nd3 to be consistent with the dipolar octupolar character