Speaker:  Professor Roger Pynn, Los Alamos National Laboratory

Title:   Spin Echo Scattering Angle MEasement (SESAME): A new approach to neutron scattering that can be developed at LENS

Abstract:   Neutron diffraction provide information about inter-atomic or inter-molecular distances, d, in a material through Bragg’s law, l = 2d sin q, where l is the neutron wavelength and 2q the scattering angle of the radiation. Obtaining precise information about d requires precise knowledge of q, which is usually obtained by defining carefully the trajectories of both the incident and scattered neutrons with collimators or slits. Unfortunately, the better one defines neutron trajectories, the lower the scattered intensity and the statistical precision of the measurement. In this talk I will discuss an alternative strategy that allows the scattering angle for each neutron to be coded into its spin state. My colleagues* and I have carried out a series of experiments at the HMI reactor in Berlin to demonstrate that the new method can be implemented using thin films of soft magnetic material (permalloy) to control the precession of neutron spins. I will show that we have achieved scattering angle resolution of ~0.05º using a very simple and inexpensive apparatus. We have applied this method to the separation of specular and diffuse reflection from planar samples and have also attempted to measure in-plane structure in thin copolymer films. I will show that the new method can be used at pulsed neutron sources as well as at steady-state sources and that it opens the prospect for innovative new neutron scattering instruments that could be developed and tested at the new LENS facility. I will argue that the university setting, as well as the technical specifications of LENS, make it an ideal test bed for such novel developments.

* Mike Fitzsimmons (LANL, USA), Helmut Fritzsche (Chalk River, Canada), Marita Gierlings (HMI, Germany), Major Janos (MPI Stuttgart, Germany), Earl Johns (Seagate Technologies, USA)

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