Hi Gerry,
we use the "recipe" given in Nelson and Dettman (2001, RCM 15, p.2301).
This is a 50:50 mix of -100mesh and -325mesh chromium powder (Alfa
Aesar Items #:10147 and #10148).
I mixed the two powders in a 1l glass bottle on a pulley block. Works
fine.
On top and bottom of the reactor make sure to fill in app. 1cm of
pure 100mesh powder (see ref given above).

> Does size matter?

Always. :-) 
Finnigan recomended the -100mesh, but the reactor is "used" after
250-300 injections. The mix mentioned above is good for more than
3000 injections due to the larger surface.
My reactor is now near the end and injects no. 3211
right know.

greetings,
Robert 


-- 
Dr. Robert van Geldern
Leibniz Institute for Applied Geosciences (GGA)
S3: Geochronology and Isotopehydrology
Stilleweg 2, 30655 Hannover, Germany
phone: +49-(0)511-643-2313 (office), -2539 (lab)
fax: +49-(0)511-643-3665
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