Eur. Phys. J. C (2010) 67: 589-599
https://doi.org/10.1140/epjc/s10052-010-1327-1

Special Article - Tools for Experiment and Theory

Ultracold neutrons extracted from a superfluid-helium converter coated with fluorinated grease

¹ Physik-Department E18, Technische Universität München, 85748, Garching, Germany
² Institut Laue-Langevin, B.P. 156, 38042, Grenoble, France
³ Forschungsreaktor München FRM II, Lichtenbergstrasse 1, 85747, Garching, Germany
⁴ Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
⁵ Paul Scherrer Institut, 5232, Villigen PSI, Switzerland

^* e-mail: zimmer@ill.fr

Received: 17 October 2009
Revised: 25 February 2010
Published online: 27 April 2010

Abstract

We report experiments on the production of ultracold neutrons (UCN) in a converter of superfluid helium coated with fluorinated grease (fomblin). We employed our special technique of window-free extraction of accumulated UCN from the superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. The fomblin-coating reduced the time constant for UCN passage through the extraction hole by a factor three compared to our previous experiment employing an uncoated stainless steel vessel. A time-of-flight measurement of the cold neutron spectrum incident on the converter, combined with a gold foil activation, allowed us to determine both the single-phonon and multi-phonon contributions to the UCN production. The UCN production rate is in reasonable agreement with the theoretical expectation.