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2% Lanthanum electrodes and radioactivity

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2% Lanthanum electrodes and radioactivity

Postby m0mri » Tue Sep 12, 2017 9:11 am

I bought some 2% Lanthanated electrodes recently (the box says Lanthanated and the tips are blue). Out of interest, I tried to measure them with my Gamma Scout Geiger Muller tube and counter. It is not an 'expensive' and accurate scintillator but it can measure Alpha, Beta and Gamma radiation.

Interestingly, it measured around twice background when offered up to the pile of 10 electrodes. I only have a few thoriated electrodes left but I recall that the reading was around the same (around 0.25 uSv/hr). The average background in Brighton, UK is around 0.1 uSv.hr.

Have anyone tested these, is this normal or could there be a chance that the rods were contaminated during manufacture (or mislabeled)?


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Re: 2% Lanthanum electrodes and radioactivity

Postby MarkL » Tue Sep 12, 2017 10:16 am

Neither thoriated nor lanthanated should emit measurable radiation when they're in the form of an electrode because the tungsten absorbs the alpha emissions. It's only when you grind the thoriated and the thorium is released that it becomes a problem. Normal Lanthanum that you dig up is not radioactive, but there are isotopes that are alpha emitters, but again it shouldn't be measurable when in the electrode. The first thing I'd try is measuring the electrodes separately from the packaging they're in to see which one is emitting. Then try wiping the emitter off really well with a damp cloth or mild solvent to be sure you get any dust or foreign material off. I can imagine a place that produces thoriated tungstens has radioactive dust floating all over the place, and it might just be on the packaging.
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Re: 2% Lanthanum electrodes and radioactivity

Postby m0mri » Tue Sep 12, 2017 2:48 pm

Dear Mark,

Thank you for the quick response. Now I am home, I just put some 2% Thoriated tungstens on test and they are reading around 10 times background (around 1uS/hr)!

I did as you suggested and cleaned the tungstens with solvent and measured them separately to their casing (as I did with the Lanthanated ones)

With the ticker on, there is clearly some alpha being read (only with the alpha window open). The measurements should not be taken as accurate doses though as my Gamma Scout is calibrated against Caesium 137.

I have, however, answered my own question by checking the Thoriated ones, the lanthanated do seem to emit some detectable radiation (in the brief time of my test and repeatably by testing background and moving to the tungstens) but the thoriated emit considerably more.

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Re: 2% Lanthanum electrodes and radioactivity

Postby Poland308 » Tue Sep 12, 2017 5:43 pm

Have you ever had an X-ray taken at the dentist or the doctors office? If so then I believe that's more exposure in one dose than you will get from putting a tungsten in your pocket for the rest of your life.
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Re: 2% Lanthanum electrodes and radioactivity

Postby MarkL » Tue Sep 12, 2017 6:35 pm

m0mri wrote:Now I am home, I just put some 2% Thoriated tungstens on test and they are reading around 10 times background (around 1uS/hr)!

Wow, I'm quite surprised at that number. I was thinking maybe they were inadvertently creating a tungsten isotope somewhere in the production process, but that would result in equal readings for both types of electrodes so clearly the rare earth materials are generating the alpha. I'll think about this a bit more.
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Re: 2% Lanthanum electrodes and radioactivity

Postby kiwi2wheels » Tue Sep 12, 2017 6:38 pm

Paranoia over radioactivity from 2% thoriated electrodes can be described as thus ;

" He (she / they) exemplified the the precautionary principle to such a degree that would have prevented evolution."
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Re: 2% Lanthanum electrodes and radioactivity

Postby raticus » Tue Sep 12, 2017 7:22 pm

I'd say if you wave the tungsten back and forth real fast between yourself and someone else standing there in your view and you can see their skeleton, then I'd say you've got an issue with that package of tungstens... Probably would want to toss those and get a new package :D
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Re: 2% Lanthanum electrodes and radioactivity

Postby m0mri » Wed Sep 13, 2017 12:17 am

Thank you and please don't misunderstand, I am not concerned about the level of radiation (certainly not with the little I weld). I have been using thoriated tungsten at home with impunity whilst aware of the 'radiation risk'.

However, as I bought some lanthanated electrodes I thought it might be interesting to compare. I wasn't expecting such a marked difference or for lanthanated to read above background. Previously, I had tried poking the electrode lengthways towards the Geiger Müller tube but it barely read above background. In these tests, I put a number of them on a table and read from the sides of the electrodes which presented a larger surface area to the detector.

Outside the body, I am happy that there is no risk from the alpha radiation emitted; I suspect that an electrode in a pocket wouldn't even irradiate the skin as the weak alpha would be stopped by clothing. If I get a moment, I might see if the dust in the garage has any detectable alpha but I suspect not with my little counter.

If I was worried about my health, I would probably exercise more and eat less but this was merely an interest.


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Re: 2% Lanthanum electrodes and radioactivity

Postby MarkL » Thu Sep 14, 2017 1:45 pm

I asked one of the physicists at work about this, here is his explanation for the observed electrode emissions.
"The lanthanum/thorium in the electrode is not only inside the tungsten but evenly distributed, i.e. there is some on the surface/close to the surface. The alpha particles will knock out electrons and create gammay rays along the chain.
With regards to lanthanum's radioactivity, i would suspect that an isotope of lanthanum is causing the radiation. A quick google shows about 1 permille lanthanum 138 in natural lanthanum, which has a very long lifetime but beta decay. Natural tungsten itself has a 1 permille tungsten 180, a long lived isotope with alpha decay. So, at the microSievert level, those all add up. Radiation from decays in the center of the electrode will be absorbed but at/close to the surface the Geiger counter will pick them up."
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Re: 2% Lanthanum electrodes and radioactivity

Postby Coldman » Thu Sep 14, 2017 3:53 pm

Gasp


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