[Neutron] source of V or V/Nb spheres for calibration; do spherical V cans exist

[mason]

Hi All
Two questions:
1. Does anyone know a supplier(s) for Vanadium spheres of diameter 2, 3, 
4, 5 etc mm. Of course null mixture V/Nb would be even better, as we 
wish to use the spheres to check the uniformity of some large position 
detectors (used for single-crystal, fibre, etc diffration.
Any advice, comments references very welcome, I know atleast 2 labs have 
used V spheres in the past.

2. Has anyone ever seen spherical V cans (wall thickness say 0.5 or 
1mm), diameter in the range roughly 5 to 12 cms, strong enough to stand 
vacuum ?
Because Al gives powder lines that severely interfere with weak 
diffraction patterns, we no longer use/advise our otherwise superb 
spherical Al  cans on our Joule-Thomson 2K cryorefrigerator. And there 
really is not enough room to insert Sollers between sample and detector.
Are there any other materials suitable for vacuum/heat shields  for 
(thermal) neutron cryorefrigerators or furnaces ?

Many thanks
Sax Mason
(Instrument D19 at ILL)

-- 
Sax A. Mason,  Institut Laue-Langevin (6 rue Jules Horowitz)  BP 156, 38042 Grenoble Cedex 9, France
Tel: +33 476 207 067 (office) (d19: ...233, sec: ...226) Fax: +33476 207 648 (or ...483 906)
e- mailto:mason at ill.eu   ill web: http://www.ill.eu/  d19: http://www.ill.eu/YellowBook/D19/help/index.html