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Standards Which Should Be Developed For EPMA Next

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--- Quote from: crystalgrower on August 02, 2018, 01:10:33 PM ---I suggested a material which is already made to see if any improvements are needed.  I understand that it is not ideal.  But it will make a useful first trial.  I just cannot assess it myself. One of the two layers is certainly free of Pb and U. The other is from Petaca  NM which has been dated and assayed before.  There is also some f the "clean" CePO4 to test separately for absence of U and Pb.

--- End quote ---

Hi CG,
I appreciate that.  Thanks.

The thing is, in order to test our zero measurements we need a synthetic monazite that has the all the elements that Mike mentioned and in the ranges that he mentioned.  Basically a zoned synthetic monazite that we *know* does not contain *any* Pb or U. 

This will allow us to test the absolute accuracy of the background positions for off-peak interferences and also test the absolute accuracy of the interference corrections for on-peak interferences.   Unfortunately a pure CePO4 doesn't really test either of those issues. And in the case of the natural composition seed crystal, knowing that the natural monazite core been analyzed previously doesn't help us either, because we can only truly trust a value of "absolute" zero (or at least a value less than the best possible EPMA sensitivity). 

As Mike said when I discussed this with him a few days ago, this sort of accuracy test is a very different way of approaching trace element standards and therefore requires a very different type of standard material than we traditionally utilize for EPMA trace element measurements.

If you want to call me some time please feel free and I can probably explain it better by skype or phone.

Mike Jercinovic:
Right, the CePO4 is certainly not that good a material for the blank test, but is, of course excellent as a primary standard (same with all the REE phosphates).  We also have a piece of the Petaca NM monazite, which is both heterogeneous compositionally as well as having lots of inclusions...  looks a lot like some of the other large pegmatite monazites from northern NM (like the Wards, Elk Mt. monazite).  Not a super useful one for us compared to some of the cleaner ones from Brazil (Minas Gerais).  Natural monazite is very useful as a secondary reference material.  For the blank testing, a synthetic monazite with at least LREEs, Th, and Y is certainly most useful.  As John says, heterogeneity is fine (even preferable), or at least of range of Th/LREE.

This is exactly the kind of detailed info that I need.  I need to use the pure CePO4 as seeds.  You can ignore its presence. 

So to confirm:  I should start with a layer of pure La-Ce-Nd-Y mix (free of U and Pb) and then add Th+Ca.  Do you care if the Ce+3 goes to Ce+4 in that Th layer? (means slightly higher Ca). 

Extra base mix can be run by XRF to show traces present. 

Mike Jercinovic:
Yes, awesome.  The Ce+3 to Ce+4 should not matter.  Only a few wt.% Y at most.  I don't think the structure will accommodate a much larger amount anyway and still stay monoclinic.


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