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The very underestimated problem of RADIOACTIVE lenses


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  • 2 months later...

OK for all you knowledgable people and know it all's and others who work in radiology and others that think they know it all, take a look at this.

Tuck it under your bed, wrap it in tinfoil. put it in a box?

P.S  The cornea of your eye is extra sensitive to radiation on this level, forget what you recieve having an X-ray or a flight to Bangkok.



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  • 3 years later...

Hello Folks, 

Just thought I'd spice up the talk and point out that although Thorium is only an alpha emitter, its "daughter" products are beta emitters, which require a bit more shielding than paper. 


So, when 232 Thorium decays, releases an alpha, and becomes 228 Radium (HL 5.7 years), which throws off an electron (-beta particle) to 228 Actinium. That lasts just over 6 hours and throws another -beta particle to a lighter version Thorium--228 Thorium (HL 1.9 yr). Next, you loose another alpha and create 224 Radium in 3.5 days, which you create something a bit nasty, 220 Radon (HL 55 seconds) then another alpha particle and 216 Polonium (HL .14 sec). Losing another alpha, you come to 212 Lead (HL 10.6 hr). Throwing another -b particle, you come to 212 Bismuth (HL 60 min), where the decay takes two different paths. 64% of the time--it throws a -b particle and you get 212 Polonium (HL 3 * 10^-7 seconds) and immediately heads to 208 Lead. 36% Lose an a particle and head to Thallium for ~3 minutes and then throw off another -b particle becoming 208 Lead, which is stable. This liberates 42 MeV per completed decay chain for one atom of Thorium. This is happening constantly. 

It's admittedly not a monster amount of MeV, however, it doesn't happen one at a time. The main problem is likely the discoloration of the Thorium doped lens element. I just don't like the idea that this wasn't revealed to us till later. I've seen stories of newer lenses still being doped with Thorium (something I'm planning on working on) well past the early 70's. 

Take this info for what you will. Just remember Thorium is not just an alpha emitter. 



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  • 11 months later...
On 4/26/2014 at 12:13 PM, Junior said:

It's one of my first posts here but not the funniest I guess…
I'm not especially talking about a magic C-lens in particular here but about a very underestimated question: radioactive lenses!
One of my friends is a fireman captain and introduced me yesterday to one of his colleagues specialized in technological risks and chemical dangers (at Poissy, France : they're known to have very great equipments.) We made 3 different tests on all my Russian lenses which are all OK excepted the Mamiya Sekor 55mm f1.4 (M42).
Here are the results:
From 5 to 10 µSV per hour (by direct touch), and 1720 shocks per second.
Element involved is Thorium 232.
They told I really shouldn't keep it. Work with it more than one hour is dangerous. It must be gifted to specialized services and absolutely not be destroyed! Or thrashed! The most dangerous exposure isn't even radiations but dusts to inhalate or ingerate (when a lens gets old it disaggregates - it's something you can't always clearly see).
I'm lucky cause until today I kept it in my basement.
So, say it please to your friends and all potential Mamiya/Takumar users that you know via websites etc, it's a strong matter of health.

i sent you a MP.

if you are willing to discuss those topics.

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