Hello there,
Today I am reporting on a test I’ve done last week on a sample of Davidite from South Australia. The sample weight is roughly 160 grams and as you can see it’s really beautiful.
My Ranger got some 17000-17500 CPM from it which is not that impressive compared with other Uranium ores I tested. By contrast the gamma activity was pretty high, from a 2000 seconds MCA data acquisition with my PDS I got an average of 1432 CPS and a dose at contact of 4.42 µSv/h.
Another thing I noticed was that putting the sample into the plastic bag the read on the Geiger counter was still about 16000-16500 CPM. The difference between the read with and without plastic bag is generally alpha radiation which therefore is lower than expected in this case. It could be a matter of geometry given that the sample is bigger than the average uranium ore I usually test, so maybe a lower percentage of alphas made it to the pancake probe.
The PDS spectrum gave me all the expected peaks from Uranium albeit the X-Rays peak from Pb214 is usually more prominent in terms of counts compared with the others. Here the “fingers” of Uranium have all a similar number of counts.
I usually get 4-5 times more counts from the 2’’x2’’ NaI(Tl) than from the PDS which made likely that the sample was going to saturate my sound card capacity.
For this measurement I didn’t use any shielding, the sample was hot enough that a simple background subtraction sufficed. Doing so I was sure to get rid of any chance, however small, of fluorescence making its way in the final spectrum.
So here’s the final spectrum, both in counts per bin and energy per bin.
No real surprise. The spectrum confirms that the Pb214 X-Rays peak is less prominent than usual. You can see that there appears to be something else close to it. It looks like a Th234 peak at 92 keV, but I didn’t put a label there because when you see the 92 keV peak from Th234 you would expect to see the 63 keV peak as well and there’s no sign of it, not even a gaussian correlation.
As mentioned above I expected the sample to saturate my sound card capacity so I didn’t try too hard to find the best possible geometry to maximise counts. Therefore the quantitative analysis is not very much significant for this one.
In summary, nice sample, expected peaks but still a thing or two to scratch your head on and even something left unresolved. So, even if it’s just another Uranium ore there’s always something to learn.
Until next time.
Massimo
