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Sampling Pm
Promethium does not have any stable isotopes. It is very difficult to obtain a Promethium sample because of its short half-life (see and availability.
The only common way is to get a sample of the luminous paint. This material is no longer produced, so if you get such a sample, it was most probably produced in the 1970's (in nuclear reactors) and most of the material has already decayed into Sm-147 by now. Even if it would be possible to obtain a fresh material, having a pure sample of this isotope in a quantity visible by human eye would be very difficult due to the high level of radioactivity. One gram of Pm-147 would emit about 0.33 Watts of decay heat.

Probably the best sample of this material has been obtained by Max Whitby of The RGB Company. There's a story about this at Theodore Gray's site over here:

Here's a photo of the paint from RGB applied to a watch hand:
You may be interested to watch this video that shows us testing our stock of Pm-147 luminous paint samples to confirm that they are (slightly) radioactive:

Our Pm paint was obtained in 2009 from a specialist Swiss company that formerly supplied luminous hands to watch manufacturers. This company in turn had sourced it from Japan. The batch we obtained was the last of their stock. It cannot be replaced and we have very little left. We do have a limited number of samples available in the form of the paint applied to watch hands. These are only very slightly radioactive, not detectably above background if you measure outside the vial in which we ship the sample.

If one makes the conservative assumption that paint on the hand originally contained 1ng of Pm-147, and that it has now undergone 15 half-lives of decay (since the Pm-147 was created in a Japanese reactor probably in the 1970s), then there will still be ~ 6 x 10^23 x 10^-9 /147 x 2^-15 which is > 10^8 atoms of Pm in the sample.

That's quite a lot or hardly any depending on your point of view!

Dr Max Whitby
RGB Research Ltd

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