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05-24-2016, 08:39 PM   #16
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QuoteOriginally posted by Digitalis Quote
Nice thought, but an LED is unlikely to output anywhere near enough UV on its own for this purpose. You would be better off getting a dedicated UV globe.
I have de-yellowed a bunch of them now with a simple LED lamp. I was skeptical also, but it works. And not only does it work, but it works fast. (24 hours is usually plenty.) I jam the lamp practically right into the lens (with foil on the other side to reflect back). This ability to really get the light just where you want it probably accounts for its ability to outperform a dedicated UV bulb that is less directional. Anyway, whatever the reason, it does the job...

05-24-2016, 08:51 PM   #17
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The LEDS in these lights are (in all probability) cheap GaN/InGaN LEDs - which have a peak emission in the UV spectrum - A dedicated monochromatic UV light source will be more efficient. UV leds would be great for this approach.


QuoteOriginally posted by dcshooter Quote
you still clinging to your completely wrong assertion that it is the balsam that yellows and not the glass?
I have been awaiting for you to give hard evidence of this. Until you do find compelling evidence that elevates your concept beyond a mere theory: my opinion stands. Molecular chains in polymers require less energy to break, do you not agree? The data I have been able to find on this phenomena is limited to crystal structures, not amorphous glass structures from what I have been able to find. The amounts of energy to deform the molecular bond of a material in its glass state is tremendous. You DO know they vitrify high level nuclear waste in glass do you? If there was even a suggestion that emitted radiation itself could cause a breakdown of the material that is used to contain it is troubling indeed.
06-02-2016, 08:46 AM   #18
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Separated doublet


Edge of doublet showing thoriated glass (right) and non-thoriated glass (left)



And a top view where you can see the yellowing effect on the image of the kimwipe below.

As an added bonus, I'll even put the yellowed under a Jansjo lamp (yes, I own one) for a couple of days and show you how effectively it deyellows this lens.
06-03-2016, 11:01 AM   #19
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What has me shocked is that no one has done this demonstration before.

06-03-2016, 04:08 PM   #20
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That's odd, because I'm sure I've seen this sort of thing done somewhere, whether here or mflenses.com or YouTube, but SOMEONE pulled a thoriated lens apart and even de-yellowed HALF the thoriated element (or the group; I don't think he separated the elements) to show it was the glass.
06-03-2016, 09:15 PM   #21
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If de yellowing really improves the sharpness of supertak, I'm in. Found my old OttLite lamp, spent 5 minutes to secure the lens. Hope it will work.
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06-04-2016, 06:42 AM   #22
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QuoteOriginally posted by Digitalis Quote
The LEDS in these lights are (in all probability) cheap GaN/InGaN LEDs - which have a peak emission in the UV spectrum - A dedicated monochromatic UV light source will be more efficient. UV leds would be great for this approach.




I have been awaiting for you to give hard evidence of this. Until you do find compelling evidence that elevates your concept beyond a mere theory: my opinion stands. Molecular chains in polymers require less energy to break, do you not agree? The data I have been able to find on this phenomena is limited to crystal structures, not amorphous glass structures from what I have been able to find. The amounts of energy to deform the molecular bond of a material in its glass state is tremendous. You DO know they vitrify high level nuclear waste in glass do you? If there was even a suggestion that emitted radiation itself could cause a breakdown of the material that is used to contain it is troubling indeed.
I suspect it is the gamma emission which causes the yellowing. Gamma rays are easily powerful enough to have an effect on any chemical bonds - regardless of the material.
06-04-2016, 07:55 AM   #23
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Yup, mild gamma emission from daughter isotopes in the Th228 decay series. The halflife of this isotope is less than 2 years, so in a 40 year old lens, you are looking at only approximately 5% of the Th228 remaining.

QuoteOriginally posted by HoustonBob Quote
I suspect it is the gamma emission which causes the yellowing. Gamma rays are easily powerful enough to have an effect on any chemical bonds - regardless of the material.


06-04-2016, 10:10 AM   #24
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QuoteOriginally posted by dcshooter Quote
Mild gamma emission from daughter isotopes in the Th228 decay series. The halflife of this isotope is less than 2 years
1.9116 years to be exact, however TH228 is an Alpha emitter.

QuoteOriginally posted by HoustonBob Quote
I suspect it is the gamma emission which causes the yellowing. Gamma rays are easily powerful enough to have an effect on any chemical bonds - regardless of the material.
Indeed Gamma rays are strong enough to do this, there is a problem: TH228 and its daughter radioisotopes are alpha/beta particle emitters.

Sources:

http://www.ld-didactic.de/software/524221en/Content/Appendix/Th232Series.htm
https://ehs.ucsd.edu/rad/radionuclide/Th-228.pdf
Table of Isotopes decay data
https://groups.nscl.msu.edu/hira/pdf/alpha_source_cal.pdf
http://www.nucleide.org/DDEP_WG/Nuclides/Th-228_com.pdf
http://www.radiochemistry.org/periodictable/gamma_spectra/pdf/th228.pdf
The radioactive series of thorium-232
http://gonuke.org/ComprehensiveTeachingToolkits/Radiation%20Protection/ChSCC...cay-series.pdf

Last edited by Digitalis; 06-04-2016 at 10:17 AM.
06-04-2016, 10:52 AM   #25
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QuoteOriginally posted by Digitalis Quote
Indeed Gamma rays are strong enough to do this, there is a problem: TH228 and its daughter radioisotopes are alpha/beta particle emitters.
I believe you are incorrect. The gamma-induced creation of "color centers" in thoriated lenses is well established* as is gamma emission from the thorium 232/thorium 228 decay sequences.

http://gonuke.org/ComprehensiveTeachingToolkits/Radiation%20Protection/ChSCC...cay-series.pdf

...specifically, figure 3...the gamma emissions are energetic release and not nuclear decay products.

In addition, the most commonly referenced survey of radioactive lenses was done using both a Geiger counter and a gamma-specific scintillation probe.

https://www.flickr.com/photos/s58y/6802092736

As for the efficacy of the IKEA JANSJÖ series desk lamp, the proof of the pudding is in the eating. I have used my JANSJÖ to clear both my Auto Rikenon 55/1.4 and ST 55/1.8. I am with you in regards to doubts about UV output from those lamps. That being said there are online sources that indicate high intensity light of a broader spectrum may be capable of dislodging valence electrons in some glass to disrupt the color centers.


Steve

* To broaden a little further, it is not just optical glass. There is an entire industry dedicated to coloring plain and doped glass with gamma radiation.

Last edited by stevebrot; 06-04-2016 at 03:02 PM.
06-04-2016, 11:48 AM   #26
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Was about to respond in a similar vein to Steve, but he seems to have beaten me to it. Anyway, it seems you have a profound misunderstanding of the way radiological decay works. Just because something decays in an alpha or beta decay mode does not mean that it does not emit gamma radiation. Alpha and Beta decay are the processes by which isotopes transmute into other elements through the emissions of particles (proton/neutron in alpha and electron/positron in beta). Gamma decay results from excited state electrons returning to a ground state and as a result releasing a high energy photon, with the isotopic number and element remaining the same, and frequently occurs after an Alpha or Beta decay.

Some amount of gamma emission occurs at after each decay in the TH228 decay chain. As you can see in the chart below, the daughter isotopes of Th228 are all comparatively very short-lived and more radioactive:


As a result, they are going through several decays in quick succession and releasing substantially more gamma radiation per given unit of time than the initial TH228 decay, with a half-life of 1.9y does.

Incidentally, the primary thorium isotope in the Thorium oxide salts used in the glass is Th232, which has a very long half life of 1.40 × 10^10 year (i.e. it is quite mildly radioactive) so those who point to the decay sequence of 232 rather than the naturally co-occurring 228 as the culprit for yellowing are doubtlessly mistaken.

Bottom line: once again, you don't understand what it is that you are talking about.

Last edited by dcshooter; 06-04-2016 at 04:29 PM.
06-04-2016, 03:00 PM   #27
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QuoteOriginally posted by dcshooter Quote
Incidentally, the primary thorium isotope in the Thorium oxide salts used in the glass is Th232, which has a very long half life of 1.40 × 1010 year (i.e. it is incredibly mildly radioactive) so those who point to the decay sequence of 232 rather than the naturally co-occurring 228 as the culprit for yellowing are doubtlessly mistaken.
This is technically true, though in practice both Th232 and Th228 would have been present in the original "dope" along with a full complement of daughter products from both isotopes. Some participation from Ac228 (very hot stuff) in gamma emission cannot be ruled out.


Steve

* Th232 decays to Th228 via Ra228 and Ac228...

Last edited by stevebrot; 06-04-2016 at 03:15 PM.
06-04-2016, 03:14 PM   #28
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QuoteOriginally posted by monochrome Quote
What has me shocked is that no one has done this demonstration before.
QuoteOriginally posted by pathdoc Quote
That's odd, because I'm sure I've seen this sort of thing done somewhere, whether here or mflenses.com or YouTube, but SOMEONE pulled a thoriated lens apart and even de-yellowed HALF the thoriated element (or the group; I don't think he separated the elements) to show it was the glass.
That would be PF user @glasbak who posted his results...

Radioactive Pentax Takumar lenses.


Steve
06-04-2016, 04:05 PM   #29
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QuoteOriginally posted by stevebrot Quote
That would be PF user @glasbak who posted his results...
Yep, that's the one I remember.
06-04-2016, 04:37 PM   #30
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Yeah, I suppose you are right, inasmuch as a portion of the TH228 is itself a daughter product of Th232 decay. Either way, the point of gamma emissions at multiple steps along the way holds true.


QuoteOriginally posted by stevebrot Quote
This is technically true, though in practice both Th232 and Th228 would have been present in the original "dope" along with a full complement of daughter products from both isotopes. Some participation from Ac228 (very hot stuff) in gamma emission cannot be ruled out.


Steve

* Th232 decays to Th228 via Ra228 and Ac228...
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