Diffuse reflection of ultracold neutrons from low-roughness surfaces

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Atchison, F. ; Daum, M. ; Henneck, R. ; Heule, S. ; Horisberger, M. ; Kasprzak, M. ; Kirch, K. ; Knecht, A. ; Kużniak, M. ; Lauss, B. ; Mtchedlishvili, A. ; Meier, M. ; Petzoldt, G. ; Plonka-Spehr, C. ; Schelldorfer, R. ; Straumann, U. ; Zsigmond, G. (2018)

We report a measurement of the reflection of ultracold neutrons from flat, large-area plates of different Fermi potential materials with low surface roughness. The results were used to test two diffuse reflection models, the well-known Lambert model and the micro-roughness model which is based on wave scattering. The Lambert model fails to reproduce the diffuse reflection data. The surface roughness b and correlation length w , obtained by fitting the micro-roughness model to the data are in the range 1$ \le$ b $ \le$3 nm and 10$ \le$ w $ \le$120 nm, in qualitative agreement with independent measurements using atomic force microscopy
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