Temperature dependence of the probability of "small heating" and   spectrum of UCNs up-scattered on the surface of Fomblin oil Y-HVAC 18/8
  We performed precision measurements of the probability of small heating and spectrum of UCNs up-scattered on the surface of hydrogen-free oil Fomblin Y-HVAC 18/8 as a function of temperature. The probability is well reproducible, does not depend on sample thickness and does not evolve in time. It is equal (9.8+-0.2)10^(-6) at the ambient temperature. The spectrum coincides with those measured with solid-surface and nanoparticle samples. Indirect arguments indicate that spectrum shape weakly depends on temperature. Measured experimental data can be satisfactory described both within the model of near-surface nanodroplets and the model of capillary waves. 
V.V. Nesvizhevsky, A.Yu. Voronin, A. Lambrecht, S. Reynaud, E.V.   Lychagin, A.Yu. Muzychka, G.V. Nekhaev, A.V. Strelkov
physics.ins-det nucl-ex