As mentioned above, quartz glass is a widely used material for constructing polarised 3He containers. However, there are a number of problems which are still unsolved. The preparation of the cell is not reliable and the relaxation times vary from 60 to 200 hours. The transmission of cold neutrons through a quartz cell is too low and the diffuse scattering of neutrons by the glass increases the background, both of which penalize the quality of the experiments.

On the other hand, it has been shown by colleagues that other types of glass and coatings as well as other coating techniques or pre- and post-treatments may result in improved cell properties. For example, rubidium coated GE 180 cells made by T. Gentile at NIST show very impressive results (relaxation times up to 800 hours). The diffuse scattering can be reduced thanks to the use of monocrystalline windows (see photo), while other coating materials like Cs suboxides or Rb are promising to increase the life-time of the spin filters. A further investigation of the Cs coating technique presently used should also reveal the recipes necessary for routinely obtaining long relaxation times. All partners have some experience on this topic and will contribute to the improvement of the properties of the 3He containers in close collaboration.

One of the very convenient properties of the 3He neutron spin filter is that it can be made in virtually any desired shape. This property has not been fully exploited yet but can obviously open up new perspectives for instruments using large position sensitive detectors like Time-Of-Flight beamlines or modern Triple-Axis spectrometers and diffuse scattering diffractometers using a flat-cone option (multi-analyser/multi-detector system). Development work will be pursued in this direction by participants P1, P2, P3, P6 and O3 with the aim to add a polarisation analysis option on a selected list of instruments.

Here are the main objectives:

• Development of high-quality valve-sealed cells for SEOP to permit comparisons of various gas compositions in an identical environment,
  
• Work on the preparation of 3He cells with the help of O1 and O2 for improving the wall relaxation time, the neutron transmission, and reducing the diffuse scattering. P1/Tyrex filling station will be made available to NSF–JRA participants for testing new cells (materials, coatings, valves, etc.),
  
• Design study, construction and neutron tests of large 3He containers to be used on three-axis spectrometers, diffuse scattering diffractometers and time-of-flight instruments.