Uranium Ore from Wittichen

[GigaBecquerel]

Hello there!

Last time I visited the Atomkeller in Haigerloch here in germany I also collected a few hot rocks from Wittichen, an area with many silver mines closeby.
It was a pretty spontanious trip, so I had no proper blacklight with me and looked for the stones just with a plastic scintillator on my ludlum, going by count rate. I guess this is why I mostly got Ra containing ore, and none containing "pure" U.

Yesterday a friend of mine was looking for a check source for his geiger counter, so I selected a stone with ~1 µSv/h and took a spectrum to confirm it actually contained U, that was important to him.
Here's the result of a over night measurement, done with a 2x2" NaI well detector, but with the sample not in the well because it's too big.

U235.PNG (67.42 KiB) Viewed 13761 times

Bi214.PNG (69.07 KiB) Viewed 13761 times

You can nicely see the "radium hand", a few U peaks and how the efficiency drops off with energy.
I am surprised how little drift I got, I calibrated the detector a few days ago and in the mean time the outside temperature dropped by 10 k, but it still seems to be perfect!

Lukas

[Geoff]

No natural ore will be pure uranium, except maybe andersonite freshly precipitated from uranyl rich mine runoff.

[GigaBecquerel]

Maybe pure wasn the right word, I meant stones with a higher U / Ra ratio.
The ²³⁵U peak is quite small compared to the ²²⁶Ra one, and some stones didn't even show the peak at all!

While looking for some data to compare the isotopic ratio I found this presentation, might be interesting for some here:
https://www.osti.gov/servlets/purl/1525592

[Sparky]

I find this thread interesting.

Regarding disequilibrium, a friend loaned me a piece of Liebigite (see his mindat link below). My spectrum of it showed vey little of the decay chain below Pa234m. In this it resembled Fiestaware more than any U mineral I have ever looked at. In the attached spectrum, I misidentified the peak at 186 as Ra226, when it is almost certainly U235, because none of Radium's daughters are present. Giga's OSTI presentation discusses the interference between Ra226 and U235 at 186 (page 32). I have often wondered how much of this peak is from Ra226 and how much from U235. Now I know.

https://www.mindat.org/gallery-51285.ht ... ter+Search

[Peter-1]

hello Lucas,
nice to see a new member from Bavaria. My question about the stone. Can you find such stones in the wild in this area, or do you have to search for them? I have a fairly pure U sample as UO2. A black powder. It does not show any decay products yet. A soil sample from Gottow from the old research institute is also good.

Peter

[GigaBecquerel]

Sparky,
I'm glad the presentation helped you!
A sample like yours is what I'd consider "pure" uranium.

Peter,
I got the stone from this exact pile of rubble:
https://www.google.com/maps/place/48%C2 ... d8.3414951

The normal ground there isn't too hot, but basically every artificial pile you can find is active.
That's the only place I found natural uranium so far, there's a warm spot near my house, but it's all just Radium.
I have not looked much for ores in the nature, but I plan to do more!

Lukas

[Sparky]

"but it's all just Radium"

Lukas, as the Presentation explains (p30), Natural Uranium in equilibrium with progeny (ore) has a spectrum that very much resembles Radium. I think if you found a mineral with a Radium spectrum, it probably has Uranium also. Ra226 only has a 1500 year half life. Without U238, the mineral would run out of Ra226 in a few hundred thousand years. In Geologic terms, very quickly.

Attached is a spectrum of a Radium watch hand superimposed on that a of Mosasaur Tooth. You can see the indications of Uranium at 63.6 keV and 92.6 kev (Th234) as explained on page 32, but most of the two Spectrums are identical. The tooth is probably better at showing this difference on the low energy end than most mineral specimens because the U is right at the surface in the enamel of the tooth and there is less self-shielding. By the way, these teeth are cheap and come from Morocco.

[iRad]

I lost one of my teeth... has anyone seen it?

[Sparky]

Very funny Tom. Your just jealous of my cool tooth. Actually it does resemble candy corn a bit.

[GigaBecquerel]

Sparky,

I know how decay chains work and what an equilibrium is.
But minerals never grow undisturbed and have perfect equilibrium. Decay products have different chemical properties, and can be washed out by weather.
All I'm saying is that when I was looking for those stones I went for pure gamma activity, which led me to find stones with a high Ra content.
I put them all on my spectrometer and looked for the U235 peaks at 109 and 143 keV, as that's an easy way to identify if there's any U at all in there and a few didn't show those peaks at all. And yes, they're small enough to make self shielding negliable.
I'll happily provide the spectra next time I cool my HPGe down.