RE: U-234 content of uranium

["Bradshaw, Keith" <Keith.Bradshaw@nnc.co.uk>]

> -----Original Message-----
> From:	Udo Gerstmann [SMTP:gerstmann@gsf.de]
> Subject:	U-234 content of uranium
> 
> Radsafer,
> 
> who knows how to calculate the amount of U-234 in uranium (with
> arbitrary enrichment factors)?
> 
> Thank you very much!
> 
> 
	I found this to be a far from easy problem, particularly if you have
the requirement for the sum of atom%'s to be exactly 100%.  According to one
reference, the 234U enrichment factor is something like 1.2 times the 235U
factor, so that's one angle of attack on the problem.

	Another is based on the following:

	Rucker TL and Johnson jr. CM (1998) "Relationship between isotopic
uranium activities and total uranium at various uranium enrichments",
Journal of Radioanalytical and Nuclear Chemistry vol 235 (1-2) 47-52.

	This gives some empirical equations for calculating ratios from
various measurements.  One such is:

	234U/235U act ratio = 27.18+0.3004(238U/235U act ratio) +
0.00143(238U/235U act ratio)^2

	You can of course modify this to atom% if you know the decay
constants.

	Rucker and Johnson don't give any uncertainties on the fitted lines.
Also much the work is done by weight%, not atom%, which further complicates
things.  If you try and do a complete isotopic composition using their
relationships, you can't quite get it all to total 100%, which shows that
they cannot be that accurate.  If you get this article, make sure you take
the equations from the figures, not the text, as there are several misprints
there.

	In any case, the relationships are very dependent on the design of
the cascade, whether re-cycled uranium was used as feed, or whether the
uranium you are measuring is actually a mixture of different enrichments.
Also I suspect their data applies only to gaseous diffusion enrichment.  I'm
not at all sure what happens in gas centrifugation.  Since the separation
factor is a LINEAR function of atomic mass in this case (rather than inverse
square (?) for gas diffusion), the enrichment of 234U may be even greater.
Perhaps someone out there can put us straight on that one.

	Personal thoughts only

	Regards

	keith.bradshaw@nnc.co.uk

	END








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