Uraninite from Piemonte - Sample 2

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Go-Figure
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Uraninite from Piemonte - Sample 2

Post by Go-Figure » 29 Mar 2021, 01:35

Hello there,
Here I am to report on the second Uraninite specimen from Valle Antrona, Piemonte, a northwestern region of Italy. You can read about the first one here https://www.gammaspectacular.com/phpBB3 ... c85b3e0954
I took a while to post this because I’ve been sent some more sample to test so the spectrometer was busy lately, more on this in the next few weeks.

Uraninite, also known as Pitchblende, is the mineral from which Marie Curie isolated Radium. The hot part of this particular sample is the black spot pointed by the red arrow. The sample weights around 30 grams.
01-DSC01317_FC.jpg
As mentioned in the previous post, this second sample is way hotter than the first one, as it was immediately obvious from the Geiger counter response, 28KCPM, not bad.
02-DSC01797R.jpg
That was already a strong indication that the shield wasn’t really going to be needed for this one, and the PDS confirmed it. Half an hour was enough to get 1.8 million counts, 1020 CPS in a room where the background with this device is around 50 CPS.
03-DSC01326R.jpg
Typical Uranium peaks showed in the result (linear and logarithmic).
04-Uraninite 2 - 1800 Secs - LIN - 13-02-21.png
05-Uraninite 2 - 1800 Secs - LOG - 13-02-21.png
Even testing such a hot sample I recorded a 24 hour (unshielded) background. For the second time I calibrated with a Cs137 check source including the weak K40 peak that form from the background. It only takes a few minutes for the Cs137 peak to fully shape using the check source, but I extended the calibration time to give time to the K40 peak to form as well. A third calibration point improves the result at high energy, I used to do that with a first calibration with Cs137 and a second with Th232, which worked fine but doing it like this is more efficient.
06-Background Recalibrated - 24 Hours - Counts x Bin - NO Shield - 0.042 Gauss - 07_08-02-21.png
06-Background Recalibrated - 24 Hours - Counts x Bin - NO Shield - 0.042 Gauss - 07_08-02-21.png (55.79 KiB) Viewed 1716 times
I didn’t expect surprises from the sample, but the result wasn’t exactly as I anticipated, the low energy part of the spectrum in particular is slightly “higher” than it should be.
The X-rays peak from Lead 214 is not far from where it should be and figuring only as a bump is a bit tricky to “locate” exactly, but the expected Th234 peak at 92.58 keV appears to be at 101 keV which is nearly a 10% discrepancy. I even considered the possibility that that peak wasn’t Th234, because in my experience it’s not usually as strong as the 77 keV, while here it’s strong enough to overwhelm it, besides, I couldn’t identify the other Th234 peak at 63 keV. In the end I couldn’t find a credible candidate for such a prominent peak from an Uranium ore, but I am open minded about it in case anyone has any suggestion about it.

I have to say this slight calibration issue at low energies reflects also in the first Uranium 235 peak, which is here at 150 keV instead of 143 keV, and in the Uranium 235 + Radium 226 peak which is supposed to be at 186 keV, but it’s around 190 keV here.
Lead 214 peak at 242 keV is almost exactly where it’s supposed to be. So it could be a calibration issue peaking around 90-100 keV and getting smaller going “north”. The strange thing is that nothing like that emerged in the background.

The rest is pretty straightforward.
07-Uraninite 2 Valle Antrona - ID - 3 Hours - RC BG Subtraction - Counts x Bin - NO Shield - 0.042 Clean - 08-02-21.png
08-Uraninite 2 Valle Antrona - ID - 3 Hours - RC BG Subtraction - Energy x Bin - NO Shield - 0.042 Clean - 08-02-21.png
Quantitative analysis: 1500 CPS from the sample versus 259 CPS from the background, as usual the percentage difference is significantly smaller than the one emerging from the PDS, mainly because the portable device allows to put the sample closer to the crystal.
09-Spectrum Analysis-001.jpg
More Uranium ores to come as soon as I have time to put together a report.

Until next time.

Massimo

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Sesselmann
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Re: Uraninite from Piemonte - Sample 2

Post by Sesselmann » 31 Mar 2021, 21:48

Massimo,

I always enjoy reading your reports, so professional. Your spectra are also perfectly smooth, I guess this is because you are subtracting a very long 24 hour background spectrum.

Thanks for sharing.

Steven

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Go-Figure
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Re: Uraninite from Piemonte - Sample 2

Post by Go-Figure » 05 Apr 2021, 06:46

Sesselmann wrote:
31 Mar 2021, 21:48
Massimo,

I always enjoy reading your reports, so professional. Your spectra are also perfectly smooth, I guess this is because you are subtracting a very long 24 hour background spectrum.

Thanks for sharing.

Steven
Yeah, I remember when doing a 6 hour measurement during the weekend felt like a very long affair, I used to stay there almost all the time as the accumulation was in progress.
Then I've learnt that, once calibrated, your instrument works more than fine without me around :)

Massimo

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