REALIZATION OF A BROAD-BAND NEUTRON SPIN FILTER WITH COMPRESSED, POLARIZED HE-3 GAS

The strongly spin dependent absorption of neutrons in nuclear spin pol arized (3) (H) over right arrow e opens the possibility to polarize be ams of thermal and epithermal neutrons. An effective He-3 neutron spin filter (NSF) requires high He-3 nuclear polarization as well as a fil ter thickness corresponding to a gas amount of the order of 1 bar1. We realized such a filter using direct optical pumping of metastable He- 3 atoms in a He-3 plasma at 1 mbar. Metastable exchange scattering tr ansfers the angular momentum to the whole ensemble of He-3 atoms. At p resent 3 x 10(18) He-3-atoms/s are polarized up to 64%. Subsequent pol arization preserving compression by a two stage compressor system enab les to prepare NSF cells of about 300 cm(3) volume with 3 bar of polar ized He-3 within 2 h. He-3 polarizations up to 53% were measured in a cell with a filter length of about 15 cm. By this cell a thermal neutr on beam from the Mainz TRIGA reactor was polarized. A wavelength selec tive polarization analysis by means of Bragg scattering revealed a neu tron polarization of 84% at a total transmission of 12% for a neutron wavelength of 1 Angstrom.