Mildly to weakly radioactive samples

[D.]

Hi All,

Question: Would something like Coltan ore, damage detectors or hardware inside an EPMA (JEOL)? The BED is pretty close to the sample ofcourse.

Interwebs says following for coltan: Bq g(-1) are 10.75 +/- 5.11 for (238)U, 7.06 +/- 3.39 for (226)Ra, 1.75 +/- 0.85 for (232)Th, and 1.63 +/- 0.52 for (40)K.

Thanks,
Deon.

[Nicholas Ritchie]

A Bq is a very small unit - a decay per second.  Most of the decay particles will be alphas of around 5 MeV.  Most will be absorbed within the sample assuming it is gram sized (the alpha path length is 10s of microns).  If the sample is microscopic in size (milligrams or less) then the number of actual decays will be tiny (<< 1/s).  The occasional alpha will escape the sample.  The very occasional alpha may strike a detector and is likely to do some very localized damage.
I've worked with samples that while very small are much more radioactive for years without incident.  I suppose it is possible that an alpha could punch a hole through an ultra-thin EDS window.  I haven't had it happen.  Similarly, an alpha could degrade a solid state backscatter but it would be very localized and wouldn't be noticeable.
In short, I don't worry about it with my instrument and haven't noticed an issue in 20+ years.

[D.]

A Bq is a very small unit - a decay per second.  Most of the decay particles will be alphas of around 5 MeV.  Most will be absorbed within the sample assuming it is gram sized (the alpha path length is 10s of microns).  If the sample is microscopic in size (milligrams or less) then the number of actual decays will be tiny (<< 1/s).  The occasional alpha will escape the sample.  The very occasional alpha may strike a detector and is likely to do some very localized damage.
I've worked with samples that while very small are much more radioactive for years without incident.  I suppose it is possible that an alpha could punch a hole through an ultra-thin EDS window.  I haven't had it happen.  Similarly, an alpha could degrade a solid state backscatter but it would be very localized and wouldn't be noticeable.
In short, I don't worry about it with my instrument and haven't noticed an issue in 20+ years.

Great, thank you Nicholas, I appreciate your insight.

[Mike Matthews]

RA can damage SDD detectors but at the levels you're quoting I agree with Nicholas that it shouldn't be a problem. If you do decide to go ahead I'd check for any measurable dead time and/or spectrum on you EDS with no electron beam. If you see anything different to without the sample you may be doing some detector damage.

[D.]

RA can damage SDD detectors but at the levels you're quoting I agree with Nicholas that it shouldn't be a problem. If you do decide to go ahead I'd check for any measurable dead time and/or spectrum on you EDS with no electron beam. If you see anything different to without the sample you may be doing some detector damage.

That's a good suggestion, thanks. (Unfortunately I don't have EDS on the probe...so that particular problem goes away).