O. Shahal

Out-of-plane orientation of multilayer N2 films adsorbed on Grafoil at 20 K

A study of the out-of-plane tilt angle of adsorbed 15 N 2 molecules on Grafoil using the nuclear resonance photon scattering (NRPS) technique is presented. Molecular coverages between n=0.6 and 5.0 commensurate monolayers (CML) at 20 K were studied. The tilts were determined by measuring the anisotropy ratio of resonantly scattered intensities from the 6324 keV level in 15 N with the photon beam parallel and perpendicular to the Grafoil planes. The results at n≤1 CML are in good agreement with calculations based on molecular dynamic simulations (MDS). At n>1 CML, it was possible to deduce only the average tilt angle of N 2 molecules over all layers. However, by relying on the reported structural properties of N 2 multilayers obtained by n-diffraction (ND), the tilt of N 2 molecules in the various layers was deduced and compared with theoretical expectations. The measured anisotropy ratios seem to rule out the occurrence of a pinwheel (PW) structure at n<2.7 CML predicted by MDS and Monte Carlo (MC) calculations.

Photoexcitation of 50Cr, 53Cr and the Debye Temperature of Chromium

The random photoexcitation process of n‐capture γ‐rays was used for studying the decay properties of the 8888 keV level in 50Cr and a level at 7646 keV in 53Cr. The γ source was obtained from the Fe(n,γ) reaction. The scattering cross section σs from the 8888‐keV level was measured in the range 297 K–10 K and the Debye temperature of metallic chromium was found to be Θ=510±20 K. The result is compared with that obtained by other methods.

Rayleigh Scattering of N-Capture γ Rays

Nine γ-lines in the energy range 0.4–3 MeV, produced by the Ni(n,γ) reaction, were scattered from targets of C, Cu, Ta, In and U, at θ=1.02°. Differential cross sections were measured relative to C. Rayleigh (R) scattering dominates the scattering cross section and the results were found to agree fairly good with calculations using the form-factor approximation.