ELSEVIER Physica B 241 243 (1998) 56 63 lllllla W. Heil a'*, 3He neutron spin filter at ILL K. Andersen a, D. Hofmann b, H. Humblot a, J. Kulda a, E. Lelievre-Berna a, O. Schfirpf c, F. Tasset a lnstitut Laue-Langevin. Avenue des" Mar~rs-BP 156, 38042 Grenoble Cede.,: 9. France b lnstitutJiir Physik, 55099 Universitiit Mainz, Germany c Technische Universitiit Miinchen, 85747 Garehing, Germany Abstract The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize neutrons over the full-spectrum of cold, thermal and epithermal neutrons. At ILL a neutron spin filter (NSF) development started which uses the direct optical pumping of metastable 3He atoms in a 3He plasma at 1 mbar. At present 0.5 bar 1 of gaseous 3He can be polarized within 1 h. Subsequent polarization-preserving compression by a two-stage compressor system enables one to prepare NSF cells of about 300 cm 3 volume in the required pressure range of several bars. A remote type of operation based on relaxation times of up to 100 h has been demonstrated in a first survey of experiments. Two representative examples are discussed which demonstrate the high potentiality for many polarized neutron-scattering applications. ~,? 1998 Elsevier Science B.V. All rights reserved. Keywords: Optical pumping; Relaxation; 3He filling station; Neutron spin filter; Polarization analysis; Parity violation 1. Principle of a 3~[e-neutron spin filter Polarized neutron scattering plays a key role in the microscopic understanding of the static and dynamic properties of magnetic materials. Like no other method it combines spatial and temporal resolution on an atomic level with the possibility to distinguish magnetic level exitations or coherent and incoherent processes. The main limitations which prevent so far a broad application of polar- ization analysis are the notoriously low counting rates to be traced back to the beam intensities *Corresponding author. Fax: + 33 4 76 48 39 06; e-mail: heil@ill.fr. which are set clear limits by the present neutron sources and the insufficient efficiency of existing polarizer- and/or analyzer devices. At present cold and thermal neutrons are com- monly polarized by supermirrors, soller guides or Bragg scattering from magnetized single crystals [i]. An evident advantage of these polarizers is their simple operation. On the other hand, they suffer clearly by severe restrictions regarding the range of energy and the scattering angle, in other words the phase space, which is accepted by these instruments. Therefore, the alternative of broad- band filters based on spin-dependent scattering or absorption, has been considered for a long time. For instance, a polarized proton target might serve 0921-4526/98/$19.00 ~(~. 1998 Elsevier Science B.V. All rights reserved PII S0921-4526t97)0051 1-5