[ RadSafe ] Question on Am/Cm fractionation

[Arvic Harms]

Please delete if you are not interested in alpha spectrometry (and Am and Cm)


Dear all,

The chemical properties of curium and americium (as trivalent cations) are generally thought to be very similar. 

However, some results in the latest NPL Environmental Radioactivity Proficiency Test Exercise 2007 (http://www.npl.co.uk/server.php?show=ConWebDoc.2309) suggest a partial fractionation of Am and Cm with standard methods of analysis. All participants used Am-243 as the yield tracer for both Am-241 and Cm-244 and while practically all Am-241 results agreed with the NPL values, about a third of the Cm-244 results showed a large negative bias. 

Could this be result of a Am/Cm fractionation during electrodeposition? 

I have posted this question on another discussion list a few days ago and I am thankful for the following helpful replies:

1. We do not see a negative bias for curium-244 vs. americium-241

2. In the Procorad intercomparisons it has been clearly shown that Cm does not follow Americium well when using extraction chromatography. Unless a "correction factor" is applied Cm can be underestimated by up to 30% using these resins.

3. Why pick on the electrodeposition step? I would think it's more likely due to some participants using a lanthanide separation step, and others not.  This is an ion-exchange or extraction chromatography separation, commonly using thiocyanate, or sometimes HCl in alcohol.

Do you have any (other) ideas why Cm and Am should behave differently (or similar)? The details submitted by the participants of the NPL PTE 2007 did not suggest any trend (ion-exchange vs. extraction chromatography and electrodeposition vs. lanthanide microprecipitation).

Kind regards,

Arvic Harms
National Physical Laboratory
Teddington
UK

-------------------------------------------------------------------
This e-mail and any attachments may contain confidential and/or
privileged material; it is for the intended addressee(s) only.
If you are not a named addressee, you must not use, retain or
disclose such information.

NPL Management Ltd cannot guarantee that the e-mail or any
attachments are free from viruses.

NPL Management Ltd. Registered in England and Wales. No: 2937881
Registered Office: Serco House, 16 Bartley Wood Business Park,
                   Hook, Hampshire, United Kingdom  RG27 9UY
-------------------------------------------------------------------