Radioactive lenses - yikes!

[Worker 11811]

Thorium only emits alpha particles. Right?

I imagine that if you account for the amount of time the average person spends in proximity to a thorium coated lens, one would be in more danger from getting a sunburn.

[benjiboy]

Thorium only emits alpha particles. Right?

I imagine that if you account for the amount of time the average person spends in proximity to a thorium coated lens, one would be in more danger from getting a sunburn.

The lenses weren't coated with Thorium,Thorium Dioxide was part of the glass recipe to make it low dispersion.

[Gerald C Koch]

Thorium only emits alpha particles. Right?

Yes and no. The most abundant isotope ²³²Th decays mainly by alpha emmision but also by spontaneous fission and very rarely emission of two beta particles. The daughter isotopes must also be considered. The principal isotope of thorium decays as follows;

²³²Th -> ²²⁸Ra -> ²²⁸Ac -> ...

Both of the first two daughters decay by beta emission. There may be a gamma emitter in the chain. If you are interested you may trace the decay chain which ultimately results in a stable lead isotope.

[Yashinoff]

Isn't anybody worried about the fact that lenses are made of glass? And glass can shatter? Scary stuff to be holding up near your eyes! Yikes!

[mopar_guy]

Problem solved:

http://www.drct.com/dss/lead/leadwear.html

[PentaxBronica]

Thank you. The people who built the original sarcophagus over the exploded Chernobyl power plant were in real danger, not the photographers who like to think more about the small amount of radioactivity of their lenses instead of what to put in front of them.

I watched a documentary recently which interviewed one of the official photographers who covered the cleanup. He went out on the roof with one of the teams shovelling debris back into the reactor building (they wore lead-lined protective clothing and were only allowed out for a few seconds - it was pretty much a case of one shovel load over the edge, then run for it). When he came to develop his film he noticed that it had marks at the bottom of the frame, caused by the radioactive wreckage he'd been walking amidst.

Given that these lenses don't appear to fog film I wouldn't worry unduly. The natural background radiation in some areas will be higher.

[tomfoo13ry]

Isn't anybody worried about the fact that lenses are made of glass? And glass can shatter? Scary stuff to be holding up near your eyes! Yikes!

Which is why I'm currently developing a lens that uses Jell-O instead of glass...radioactive Jell-O but Jell-O nonetheless.

[LarryP]

great Tom. just remember to make some in lemon orange and strawberry so we have built in contrast filters.

[Worker 11811]

The lenses weren't coated with Thorium,Thorium Dioxide was part of the glass recipe to make it low dispersion.

I thought the lenses were coated with some thorium compound to improve their optical qualities but it makes more sense the way you say it.
Thorium is IN the glass, not ON the glass... Got it!

Yes and no. The most abundant isotope ²³²Th decays mainly by alpha emission but also by spontaneous fission and very rarely emission of two beta particles. The daughter isotopes must also be considered. The principal isotope of thorium decays as follows;

²³²Th -> ²²⁸Ra -> ²²⁸Ac -> ...

Both of the first two daughters decay by beta emission. There may be a gamma emitter in the chain. If you are interested you may trace the decay chain which ultimately results in a stable lead isotope.

This is good to know.
The reason I understood things to be the way I said is because xenon lamps and carbon rods are often doped with thorium and/or other rare earth elements to improve their spectral emission characteristics.
The electrodes inside a high pressure xenon lamp are made from sintered tungsten that has a small percentage of thorium mixed in or coated on. I forget which.
Regardless, I was led to believe that as long as you don't eat them or carry them around in your pocket, moderate amounts of thorium-treated (thoriated?) materials are mostly harmless and that you stand more chance of contracting cancer from a sunburn than you do from (conscientiously handled) thorium.

Anyhow, it's good to know more about thorium and, now, I have something new to go read about.

[Newt_on_Swings]

I understand the decay of the radioactive elements in the lenses eventually turns them yellow. What I dont get is how putting the lens in bright sunlight or a UV lamp for a few days, eventually clears it up. Does anyone have an answer to that?