Samples and sample cans
Samples vary so much, and in so many respects, that what follows is necessarily incomplete but hopefully still useful. These remarks generally apply to powder samples and liquids. Single crystals are another story.
The DCS beam is 100 mm high and its intensity is essentially uniform as a function of height. The width of the beam depends on the resolution mode. In low resolution mode the width is 30 mm. In medium resolution mode it is 15 mm. The beam intensity falls with increasing horizontal distance from the beam center line. Ideally the sample should be about as tall as the beam and its geometry should be cylindrical or annular. Tall and thin is better than short and fat. In some cases a flat plate (or some other geometry) may be preferable, or the only practical solution.
Note that if you are using the NCNR's Oxford Instruments 12 Tesla vertical magnet dilution refrigerator the available height is restricted. Consult with your local contact if you plan to use this equipment.
We have several sizes of cylindrical sample cans and annular sample cans:
Annular Cans Height 100 mm Outer Can Inside Diameter 20 mm Annular Thickness (t) (see below) 0.10, 0.40 and 0.75 mm
Cylindrical Cans Height 84 and 114 mm Diameter 13 and 18 mm
One of the DCS Annular Cans,
note that the lid holds in place
One of the DCS Cylindrical Cans
Annular Can Thickness As is seen in the picture, the DCS annular cans are formed by an inner and an outer can. The annular thickness is the difference between the inner and the outer can radius.
For additional information speak to your local contact.
It is important to minimize scattering by materials other than the sample itself and those parts of the sample container that are necessarily in the beam. Depending on the sample environment and on personal preference, samples may be masked with cadmium, Gd2O3 paint, boron nitride or some other neutron-absorbing material. Alternatively, or in addition, users generally mask the incident beam.
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Last modified 25-March-2003 by website owner: NCNR (attn: John Copley)