A medium-resolution double-crystal small-angle neutron scattering (DIXIE) instrument has been completed and is in the initial testing phase. This instrument uses two spherically bent silicon crystals as monochromator and analyzer. The bent crystals coarsen the resolution while dramatically improving the peak intensity. The curvature of these crystals has the added benefit of focusing the beam spatially, which allows the use of small samples. In its current geometry, the Q-resolution is 0.0008Å-1. A Q of 0.001Å-1 corresponds to structures greater than 6000Å in size. The resolution and degree of spatial focusing can be varied, although not continuously, with the choice of analyzer reflection, curvature of the crystals and monochromator-analyzer distance. The DIXIE is equipped with motion controllers, computer and GPIB interface and all the accoutrements necessary to perform experiments on materials of interest. Currently, a commercial instrument control package, Labview, is used to run the machine. This proposal is not intended to build a new machine. The fully functional machine already exists. Experiments cannot, however, be run remotely at the present time.
The DIXIE is a good choice because it small and there is no need or
chance for the remote user to move large pieces of shielding. Any runaway
motions caused in the testing phases have very little potential for
irrevocable damage. Another reason for the choice of instrument is that
it has not yet developed a large user base and interruptions to its
operations will not impact the existing user program adversely. At the
same time, small-angle scattering is a very popular technique and SANS
instruments that are in operation are heavily oversubscribed. Hence, when
the project is completed, the potential number of researchers that will
welcome the opportunity to visit the virtual laboratory will be
substantial. Lastly, data files produced by the DIXIE are relatively
small and will not need very much effort to archive and distribute
effectively.