Consistent description of UCN transport properties

Abstract

We have investigated the diffuse reflection probabilities of Replica guides for ultra-cold neutrons (UCN) using the so-called helium method. For the first time we could establish a consistent description of the diffuse reflection mechanism for different lengths of the guide system. The transmission of the guides is measured depending on the helium pressure inside of the guides. A series of simulations was done to reproduce the experimental data. These simulations showed that a diffuse reflection probability of d = (3.0 ± 0.5) • 10 −2 sufficiently describes the experimental data.

First ultracold neutrons produced at TRIUMF

“…The experimental fall time can be matched with diffuse-reflection probabilities of 3 % to 5 %, the rise time is best matched with 3 %. This value is similar to values reported for a range of UCN guides [28][29][30] and we chose it for all subsequent simulations. The time constants slowly change with increasing valve delay times, presumably due to a slow change in the energy spectrum while the UCNs are stored in the source.…”