Temperature dependence of the probability of "small heating" and spectrum of UCNs up-scattered on the surface of Fomblin oil Y-HVAC 18/8

TL;DR

This study measures how the probability and spectrum of ultracold neutrons up-scattered on Fomblin oil surface vary with temperature, revealing consistent probability and weak temperature dependence of the spectrum shape.

Contribution

It provides precise measurements of UCN up-scattering probability and spectrum on Fomblin oil, supporting models involving nanodroplets and capillary waves.

Findings

Probability of small heating is (9.8±0.2)×10^(-6) at ambient temperature.

Spectrum shape is weakly dependent on temperature.

Data aligns with models of nanodroplets and capillary waves.

Abstract

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.