We report the first observation of the upscattering of UCN stored in a closed vessel filled with4He. The observations allow the direct determination of the production rate and hence the density of the UCN stored in the helium, which are found to be in agreement with theoretical expectations. the technique offers the possibility of studying the interactions between excitations in the liquid at regions of temperature and wavelength inaccessible to presently available methods. © 1987.
Kilvington, A. I., Golub, R., Mampe, W., & Ageron, P. (1987). Scattering of ultra-cold neutrons (UCN) by superfluid helium at temperatures around 1 K. Physics Letters A, 125(8), 416–420. https://doi.org/10.1016/0375-9601(87)90174-5