UCN anomaly and the possibility for further decreasing neutron losses in traps

Serious disagreement of an order of magnitude or higher still exists between ultracold neutrons (UCN) loss coefficients obtained in the neutron storage experiments in Be, C, solid oxygen and heavy water ice traps, and those following from transmission measurements or based on dynamical models. The cause of this anomaly is not understood yet. The only example of reasonable agreement is the case of hydrogen-free fluoropolymers where the UCN loss coefficient was obtained as low as 2x10-6 at the temperature -160 deg. C. A practical way is proposed for further decreasing neutron losses in traps using lower molecular weight, low-temperature perfluoropolymer oils for covering the trap's walls