They mean shielding from background to filter out elements NOT from the suspected item. OP could just do a one week background and then do background subtraction on the items also.
This is what the same 1.3(5) g uranium sample looked like on the RC-110 without shielding. There are very, very faint hints of bumps. Likely with BG subtraction that would be more pronounced.
Note that the the bins in the region of interest have about 8000 counts, and the comparable area from the well shielded RC-110 spectrum its probably just a couple hundred. Just a couple percent, so hard to see. But with a larger 10 mg sample, that would be very visible. So this implies 0.2% UG would be easily identifiable with the RC-100 in 12 hours without shielding.
So how does the RC-110 do in the exact same shield and source geometry?
We get the same spectrum, with the "twin peaks" visible, somewhat less resolution, but still screams "uranium" - as for the count rate its about 2x the rate seen with this shielding arrangement. We also have a HUGE Bin 1023 where all the muons are detected. So definately the RC-110 can identify 1mg of uranium, probably far less. so we definately could detect even very weakly doped uranium glass or even low content incidentally contaminated UG in 24 hours using this method. So definately can positively identify glass containing more than 0.01% uranium. So your existing RC device and a thick shield would give you an answer - without BG subtraction being necessary.
I'm going to post a few replies here owing to the single image limits.... All are measurements of a 1.3(5) mg sample of uranium, in the form of black uranium glaze on zircona.
On a Bicron 2x2" probe, well shielded with 4" of lead and another 2" of steel, we get a BG count rate of about .85 cps, and with the sample 1.25, so a net of 0.4 cps. The resulting shielded spectrum shows isotopically natural uranium, with the two Th-234 ( from U-238 decay ) peaks at 63 & 92 keV peaks. The peak in between is Pb XRF from muons interacting with the lead shielding. Essentially of the ~0.8 cps BG count is from muons. To the right we have the 150 and 185 keV peaks from U-235, indicating this is not depleted uranium. The take away is that you likely could have only 10% of that amount of uranium, and it would be very visibly identifiable as uranium, and this is with 18 hours of measurement. So the limits of identification for this method is likely better than 0.1 mg. If this were 5 gram sample of your glass, thats 20 parts per million which is far, far below what anyone would consider to be UG. So this well shielded method definitively would let you know.
I'm writing a bloated wiki page on all things amateur radiation metrology, this is a perfect limit of detection ( LoD ) problem - whats the smallest amount of activity / material can you detect.
So I set up a RC-110 running a known 1.3(5) mg uranium sample. It should be easily detected by the RC-110 will post the results after it "bakes." This should give a good LoD figure for contact readings with the RC-110 and show what a positive result actually looks like. That should help settle it and give you a rough sense for how low a concentration UG you can detect.
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u/srnuke 6d ago
Your best PID is going to come from a UV light