The Spin Polarised Hot Neutron Beam Facility

First test of an 3He neutron spin filter

The nuclei of a helium-3 gas (3He) can be polarised. Thanks to the strong spin-dependancy of the neutron absorption a bottle filled up with that polarised gas would be an effective neutron polariser even for large white beams. This technique was made trully operational for the 1st time in November 1996 by the historical experiment shown here.

  • W. Heil (left) and H.Humblot (middle) working on the 3He polariser.
  • The 3He filling station uses laser light to polarise metastable 3He atoms by optical pumping at low pressure (1.3 mbar). The resulting electronic polarisation is partially transferred to the nuclei through an hyperfine interaction. When enough nuclear-spins have been polarised, the 3He gas is then compressed in a titanium two-stage amagnetic compressor. We see H.Humblot adjusting the assembly.
  • W. Heil is removing from the compressor the long-life detachable neutron-spin filter cell filled up at several atmospheres. With the help of T. Roberts, he puts the cell in a special container to transport it to D3 without loss of polarisation.
  • W.Heil and H. Humblot carry the filter to the ILL reactor hall where A. Leadbetter is anxiously waiting for them at D3.
  • F. Tasset, H. Humblot and W. Heil install the 3He spin-filter on D3.
  • F. Tasset is looking at the ratemeter to get a first estimate of the neutron-beam polarisation.

(movie recorded by E. Lelièvre-Berna, ILL, 1996)