CAD and SimulationUltracold Neutrons

Surface Roughness Influence on UCN Transmission

Aluminum is commonly used as vacuum separation foil in neutron guides and detectors. Due to its low surface potential neutrons with angular velocities down to 3m/s are passing the foil. However, according to Steyerl [1] neutron transmission is also affected by the surface roughness of the passed foil. The transmission decreases towards slow neutrons with ~1/v², .

Hence many neutron experiments mostly need the slow neutrons I studied this behavior as side project in my thesis. Therefore, I have developed polishing techniques to achieve roughnesses for aluminium foils and neutron guides of Ra = (0.04 ± 0.01) μm and Rz = (0.10 ± 0.02) μm

(a) UCN velocity dependent transmission of a polished Ra <0.04 to a unpolished Ra 0.4.

[1] Steyerl, Effect of surface roughness on the total reflexion and transmission of slow neutrons. Zeitschrift für Physik, 254:169–188, April 1972