Accumulation and extraction of ultracold neutrons from a

6 We report experiments on the production of ultracold neutrons (UCN) in a converter of 7 superfluid helium coated with fluorinated grease. We employed our technique of window-free 8 extraction of accumulated UCN from the helium, in which they were produced by downscat9 tering neutrons of a cold beam from the Munich research reactor. The time constant for UCN 10 passage through the same extraction aperture as in a previous experiment was a factor two 11 shorter, despite a lower mean velocity of the accumulated UCN in the present experiments. 12 A time-of-flight measurement of the cold neutron spectrum incident on the converter allowed 13 us to estimate the multi-phonon contribution to the UCN production. The UCN production 14 rate inferred from two methods agrees with the theoretical expectation. 15 PACS numbers: 78.70.Nx, 28.20.Fc, 29.25.Dz, 61.12.Ha 16