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["Les Slaback, Health Physics" <SLABACK@micf.nist.gov>]

I will forward you query to the Radioactivity group for a response.
My suspicion is that they did not use a formal I-gamma, but that
it was related directly to several standards we have that are called
the Herningschmidt stds, which are themselves enclosed in glass.

We were just recently looking at the paperwork for these.  The original
certificates are signed by Curie, et al.

Because of the fragility of the blackened glass these stds have been
'retired', but are being kept for historical value.
I would presume that if yours are vintage 1947 with almost a gram of radium
that they would be worse than ours.  'Handle with care' would be an
understatement.

I send this to the whole group since this might be of general interest.

SLABACK@MICF.NIST.GOV
   ...a little risk, like a bit of spice, adds flavor to life