I have no experience with U nitrate, but lots with U acetate, which in many 
ways is rather similar. Aqueous UA when stored refrigerated (and therefore 
mostly in the dark, because it also deteriorates in light), is useable for one 
month. Made up in alcohol, at best its good for one week.
If the aqueous solution is much over a month old or was frequently left out on 
the bench, then a fine precipitate is visible in TEM, at that point clearly the 
material loses its activity.
Cheers
Jim Darley
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On Thursday, March 01, 2001 2:34 AM, Mary Bryhan 
[SMTP:mbryhan@northernhealth.org] wrote:
> Hi...  need help with a discussion in our lab... I had always thought that in
> a Snook's Retic the 1%  uranyl nitrate sol. was supposed to be fresh each
> time, but we could use it for about 2 weeks with great success.  I couldn't
> find any references so any help would be appreciated.
>
> Mary Bryhan HT (ASCP)
> Northern Michigan Hospital
> Petoskey, Michigan
>