Autunite from Nevada
Posted: 11 May 2020, 05:25
Hello there!
It’s been a while since my last post, but I used the lockdown here in Italy, which ended this past week (albeit the emergency is far from over), to record a very long Trinitite spectrum which I am going to write about in the coming days, there’s still one thing I need to check before posting it.
That’s an easier one, an Autunite sample. It’s pretty small, I can’t tell you the exact weight because it’s fixed to its little box, but it must be less than 5 grams.
It’s small but beautiful, and of course it glows under UV light, which is always a plus.
While the GS 2’’x2’’ was busy with Trinitite in a 28 days measurement (first a 7 days background, then 14 days with the sample, and finally more 7 days background) I first tested the sample with my Ranger and then with the PDS.
The Ranger gave me a respectable 3000 CPM.
The PDS told me the amount of gamma radiation from the sample was pretty low, my background is around 0.10 µSv/h and highest read I got at contact was 0.16-0.17 µSv/h, background included.
Over a 9 hour time the average was 0.14 µSv/h (always including background). In the spectrum from the PDS you cannot really tell the Autunite contribution from the background because peaks are the same, what you can see is that it makes all of them a bit more “bumpy”.
All this happened on April 4, and then I had to wait until last Friday, May 8 for the next step. Since I just finished accumulating the background for the Trinitite measurement I decided to use that as a background for this measurement as well. Calibration was several weeks old and some thermal drift was inevitable but as you can see below it held pretty well, it’s a bit off only at high energies.
I wanted this to be a shielded measurement because I will repeat it with no shield in order to see the difference and understand how much the XRF from the shielding is contributing to the 77 keV peak.
As usual I first recorded a 24 hours background. My shielding was basically the same as I my last experiments, 5 mm of plastic, 1 mm of copper, 4 mm of pewter and 13-15 mm of lead. My shield improvement has been postponed for obvious reasons.
So here’s the background spectrum accumulated in two distinct 7 day sessions for a total of two weeks. My shielded background was 61 CPS, one of my best result with this setup.
And here’s the result. Accumulation time with the sample was 40 hours.
The sample gave me roughly 43 CPS on average, which should be good enough to repeat the measurement with no shield and a simple background subtraction. Nothing strange for an uranium ore, the 77 keV peak is the highest in terms of counts, and this is often the case regardless, but it remains to be seen how much the fluorescence from shielding contributed to it.
Peaks from U235 are well visible, while those from Th234 are a bit overshadowed by the 77 keV peak, but still clearly there (and the gaussian correlations are unmistakable).
The K40 peak is a bit off, but again, the calibration for this measurement was done about a month ago, so I wouldn’t complain! And there’s more to say about that, but that’s for the next post.
Last, probably the most interesting peak of the spectrum is that at 46 keV which is clearly Pb210, it must be only the second or third time that I “catch it” in one of my spectra, so I was happy it showed up!
A few more bumps are visible at lower energies but for now I decided to leave them unlabeled.
Quantitative analysis summarizes what’s above.
In the end it was just another uranium ore, but there’s always something interesting to look for and this one in particular will have another close encounter with my scintillator in the coming days!
Hope you are all well.
Until next time.
Massimo
It’s been a while since my last post, but I used the lockdown here in Italy, which ended this past week (albeit the emergency is far from over), to record a very long Trinitite spectrum which I am going to write about in the coming days, there’s still one thing I need to check before posting it.
That’s an easier one, an Autunite sample. It’s pretty small, I can’t tell you the exact weight because it’s fixed to its little box, but it must be less than 5 grams.
It’s small but beautiful, and of course it glows under UV light, which is always a plus.
The Ranger gave me a respectable 3000 CPM.
Over a 9 hour time the average was 0.14 µSv/h (always including background). In the spectrum from the PDS you cannot really tell the Autunite contribution from the background because peaks are the same, what you can see is that it makes all of them a bit more “bumpy”.
I wanted this to be a shielded measurement because I will repeat it with no shield in order to see the difference and understand how much the XRF from the shielding is contributing to the 77 keV peak.
As usual I first recorded a 24 hours background. My shielding was basically the same as I my last experiments, 5 mm of plastic, 1 mm of copper, 4 mm of pewter and 13-15 mm of lead. My shield improvement has been postponed for obvious reasons.
- 08 - Background - 336 Hours - Counts x Bin - Shield V2-1 - 0.036 Gauss - 31-03_07-04+01-05_8-05-20.png (20.49 KiB) Viewed 8740 times
Peaks from U235 are well visible, while those from Th234 are a bit overshadowed by the 77 keV peak, but still clearly there (and the gaussian correlations are unmistakable).
The K40 peak is a bit off, but again, the calibration for this measurement was done about a month ago, so I wouldn’t complain! And there’s more to say about that, but that’s for the next post.
Last, probably the most interesting peak of the spectrum is that at 46 keV which is clearly Pb210, it must be only the second or third time that I “catch it” in one of my spectra, so I was happy it showed up!
A few more bumps are visible at lower energies but for now I decided to leave them unlabeled.
Quantitative analysis summarizes what’s above.
Hope you are all well.
Until next time.
Massimo