My latest sample is Tyuyamunite from Vanadium Queen Mine, San Juan County, Utah.
Natural Uranium is strong with this one….well, not as strong as the Autunite crystal I posted last week but still fun to test.
Version 1 had about 1.5 cm equivalent of lead, plus roughly 1 mm of copper and 5 mm of plastic and gave the reduced background you see below, -75% counts, but with a very prominent fluorescence peak at 77 keV.
- Background - CPS - 12 Hours - Counts x Bin - Shield V1 - 0.045 Gauss - 21-09-19.png (7.99 KiB) Viewed 4023 times
You can see the improvement is pretty obvious, the 77 keV peak is reduced from 0.376 CPS to 0.297 CPS. We have to consider a 77 keV peak from Pb214 would have been there anyway, as the most prominent peak in the background spectrum in terms of counts, likely around 0.26-0.27 CPS at the center of the peak even with zero fluorescence, therefore according to my estimation 4 mm of Pewter reduced fluorescence from Lead by roughly 70%.
In terms of absolute counts it had no effect, actually I had 4 CPS more than last time from the background, probably I wasn’t as good as then at assembling the shield, but it’s a tiny difference in the end, I think I can do better next time as far as this is concerned, but I will still need some more lead sooner or later.
- Background - CPS - 12 Hours - Counts x Bin - Shield V1 - 0.042 Gauss+CPS - 29-09-19.png (9.72 KiB) Viewed 4023 times
The sample gave a respectable 33K CPM at the Geiger counter, I was a bit surprised to see that figure reduced by less than 10% once the Tyuyaminite was back inside its plastic bag, where it’s going to rest for a while. When it was out of the bag I was carefull not to touch it with the probe, which wasn't a problem with the bag in between, so probably I managed to get the Geiger closer and that reduced the difference between the two figures.
According to the PDS the dose from the sample basically at contact is 0.66 µSv/h.
Another indication that fluorescence has been consistently reduced is the fact the peak at 77 keV (to which Lead 214 in the sample also contributed) is not the most prominent of the spectrum.
The rest is pretty much expected. Just like last time Bi214’s peak at 2204.21 keV was there too, but I didn't include it for the sake of a better visualisation of the rest.
Quantitative analysis shows a more than decent 802 CPS from the sample. In comparing the exposure figure to the dose from the PDS 100G measurement take into account you cannot get the sample as close to the crystal as you can do with portable units such as the PDS, therefore the difference appears justified, net of the inevitable margin of error.
Next week I won’t probably have any new sample to test, but I have something on the way, and also a new detector which will join the team shortly.
Have a nice weekend folks.
Massimo
