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Re: Thoraited Tungsten Rods

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 03:58 PM 4/17/2007, Tesla list wrote:

Original poster: William Beaty <billb@xxxxxxxxxx>

On Sun, 15 Apr 2007, Tesla list wrote:

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
> >Original poster: William Beaty <billb@xxxxxxxxxx>
> >But is this a common myth?
>
> No, it's not a myth.. the thorium emits particles which ionize (a
> very few) air molecules near the electrode.

Yes, but you're offering reasoning, not research papers or experiment.
I'm suspicious that perhaps the reasoning is flawed, and the radioactivity
actually has insignificant effect.  I'd want to see an experiment which
says who's right.
OK.. they're 2% thorium, as I recall. What's the specific activity of thorium (i.e. how many Ci per gram)? 
1 uCi = 27,000 disintegrations/sec, as I recall.
In order to reliably trigger an arc, we might need a guarantee of one stray electron in, say, 0.1 millisecond somewhere in the gap, so, to a first order, if there's 1 uCi of thorium in the rod (or at least near the end), then you're in the right ballpark.
I can't recall how hot the Co60 source we use for spark gap stabilization is at work. I'll check. 



> >    Do non-radioactive materials work almost as
> >well when put in tungsten?
>
> yes from the incandescence standpoint, no from the ionizing radiation
> to stabilize the arc standpoint

Says who?  And why do they say so?  The role of radioactivity sounds
reasonable, but that doesn't make it true.
Well.. you can be SURE that if it's not radioactive that there's no contribution from radioactive stabilization. 


  Theory does not determine
experimental results, instead you have to perform the actual experiment to
see if the theoretical arguments are supported. In other words, if we
could remove the radioactivity, would a welder actually see a noticable
difference?  (Don't say yes unless you've tried it.)  Or if we could
remove the thorium element but provide the same radioactivity, would a
welder see a noticable difference... and if there is a difference in both
cases, is one of them much larger?
I suspect that there are even more confounding factors you haven't identified. Thorium and Lanthanum, while similar, are different, both in work function, thermal properties, incandescence, and all that. It would be quite difficult to set up a series of experiments.
What I suspect is that the thorium was added first and provided a better result than pure tungsten (based on the addition of thoria to things like lantern mantles, etc.) Thorium probably because it's cheaper than Lanthanum, or historically more common. When people started to ask questions about radioactivity, they looked in the periodic table and said, Ah, I wonder if Lanthanum will work just as well.