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04-17-2016, 03:24 PM - 1 Like   #16
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Do not eat the lens!

04-19-2016, 11:40 PM   #17
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QuoteOriginally posted by Digitalis Quote
That is because it is never found in its pure elemental form. It is always mixed in with other minerals, radioactive decay products and isotopes.

Alpha particles: yes, they can be stopped by air alone. Beta particles, you will need something denser than air to stop those. Gamma particles, you need Lead bricks to effectively shield yourself from them.

Count rate does not universally equate to dose rate, and there is no simple universal conversion factor. Any conversions are instrument-specific. So your statement is basically useless, Luminox watches can set off scintillometers too you know. And people have those strapped to their wrists for years.
What the army says...

More or less this says an eyepiece of thoriated glass will give you 10% of the alpha radiation it is capable of generating. And the lens in front of the camera body then, none by inference.

However the jury appears to be out so to speak. not much authoritative info about real exposures due to use of lenses other than anecdotal stuff.

Radioactive lenses

This looks like a fair study..

"From the gamma spectra, it is clear that most camera objectives and the camera
houses rarely give higher intensities than 115% of the background radiation. Since
a simple Geiger meter was used to assist the choosing of which objectives to
measure more precisely, no objectives were chosen that gave off little or no
radiation. Thereby, the increase in activity - however slight - observed on all
measurements was expected."

"Here, is the radiation weighting factor which is equal to 1 for electrons.
Therefore, 2.77 μGy absorbed dose translates to 2.77 μSv equivalent dose. From
this, it is seen that the contribution to the annual maximum radiation dose to the
eye’s lens from this camera lens is 0.2 ‰.This is indeed a contribution, but a very
insignificant one. This amount of usage of the Carl Zeiss Tessar lens is therefore
deemed non hazardous in terms of beta radiation."

"In this case, the whole body is irradiated, meaning that the tissue weighting factor,
, is equal to 1. is given using the same calculation as in formula (9) with
. This gives an effective dose from gamma radiation from the Carl Zeiss
Tessar lens on the whole body of the photographer of 0.17 μSv. This, compared to
the standards set by the Swedish Radiation Protection Authority, is only 0.17‰ of
the maximum allowed dose."

-- my two ill educated cents in this scientific question is that given the most stringent standards the thoriated lense of the type in question do not pose a hazard..

-- if one desires perfect safety then don't come out of one's lead lined, air filtered cave until civilization is over (u might have a decent chance of surviving that long), and forage for food at night, using ir goggles and blowing your air horn to scare off what nocturnal predators that have survived.
04-29-2016, 03:46 AM   #18
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Again, I'm not afraid of any radioactive lens
And really want to have yellowed one.
I think one X-ray scan of chest will be 10 times more that having such Takumar for 50 years.
04-30-2016, 04:38 PM   #19
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UV light will discolor discolored lenses.. so to speak.. in other words clarify them.. how fast, how efficiently.. subject to trial.. UV lamps can be had in mineral prospecting stores etc...


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