My first Mystery Source (Ra226)

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Joined: 04 May 2019, 22:24

Re: My first Mystery Source (Ra226)

Post by Go-Figure » 17 May 2020, 20:04

Hi Mike.
A mistery source is always a lot of fun!

Looking at the spectrum, Ra226 is definitely there. Problem is Ra226 gamma spectrum only differs from U238 for the two Th234 at 63 keV and 92 keV and it's very easy to miss them. I tested a few uranium ores where those two peaks were completely buried in the Pb214 x-ray 77-78 keV peak.

Last year I tested a "Radium Clock" and you can see the spectrum matches yours pretty well download/file.php?id=1265&mode=view

On the other hand I see the 77-78 keV peak and it seems to me it tends to get a bit "wide" at both sides and that could be an indication that Th234 is there as well, albeit in disguise, in which case it would be U238 that we are looking at. Something similar happened with the last sample I tested, an Autunite from Nevada viewtopic.php?f=5&t=795

Mike S
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Joined: 25 Apr 2020, 10:24

Re: My first Mystery Source (Ra226)

Post by Mike S » 18 May 2020, 00:49


Good points. When I ran the sample the first time, I assumed all of the "lead peak" was from my shield. I know better now, but at the time I used the software feature (name escapes me early in the morning) to suppress that peak so the others were more visible. That process distorted the peak and added little horns. That's what I remember anyway.

From a practical standpoint, Ra226 seems like a more likely check source than U238/U235. It also seems like a lot of activity for a uranium source, but I'm new to this, so my intuition isn't calibrated.

I haven't gone back and done any additional tests on this sample since I've been distracted by other samples and equipment upgrades and repairs.

I like the spectra you've done. I especially like your attention to detail and the way you document them clearly and completely.

Mike S.
Mike Sullivan
Central Coast of California, USA

Posts: 29
Joined: 01 Dec 2019, 13:58

Re: My first Mystery Source (Ra226)

Post by Sparky » 21 May 2020, 01:42

I have had a closer look at the region between the Th234 peak at 63 and 92 keV with my Moroccan Mosasaur Tooth. This tooth always presents better details in this region than my other U minerals. I believe the tooth does better here because it is relatively weak and does not produce a lot of backscatter noise. The Uranium also appears to be concentrated on the surface. The lower energy lines are better represented here than in a rock that has more self-shielding.
I overlaid a Bauer (think Fiestaware) Natural Uranium spectrum on top of the Tooth’s spectrum. This gave me three lines in the region to confirm proper linearization: the two for Thorium and a Ka1 lead florescence line at 75 KeV from lead in the glaze. Incidentally this overlay clearly shows the difference between recently separated Uranium and Uranium in equilibrium with progeny.

I think that the main peak with the tooth at 77 KeV may be a composite peak of the following kA1 x-rays:
Lead 74.96 keV
Bismuth 77.10 keV
Polonium 79.30 keV

These x-rays are all listed in G. Gilmore’s Appendix C.1 as associated with isotopes in the U238 decay chain.
The tooth also builds a small, bumpy “shelf” on the right side between 85-90 keV. The Thorium peak , which I previously thought was on this “shelf”, is actually just a change in slope further out on the skirt of the general feature. I think this bumpy ”shelf” is the kB1 x-rays of these same elements:

Lead 84.92 keV
Bismuth 87.34 keV
Polonium 89.81 keV

That is my theory, anyway. The paper, linked below, has a HPGe detail of this same region in Fig. 1. It is even more complicated than I have outlined. Unfortunately, they do not identify the peaks in the detail.

I just wanted to correct my previous post identifying that horn poking out right side of the skirt of the general feature as being Th234 at 92. I now think it is probably from Polonium x-rays at 90 keV. ... _05003.pdf
Mosasaur Tooth in shield.png
M Tooth and Bauer2.png
Michael Loughlin

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