Superfluid helium film may greatly increase the storage time of ultracold neutrons in material traps

We propose a method to increase both the neutron storage time and precision of its lifetime measurements by at least tenfold. The ultracold neutrons (UCN) in material traps now provides most accurate is used many other experiments. these limited interaction UCN with trap walls. show that covering walls liquid helium may strongly decrease losses from traps. $^4$He does not absorb all. Superfluid He covers as thin film, $\sim 10$ nm thick, due van der Waals attraction. However, this film on flat wall too protect their absorption inside material. By combining attraction capillary effects we surface roughness thickness much beyond penetration depth 33$nm. Using for requires low temperature $T<0.5$ K avoid vapor, while because waves are small can be accounted using linear dependence.