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04-25-2019, 10:59 AM   #46
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regarding the banana K-40 makes up 0.012% of potassium atoms.

Th-232 makes up 99.98% of Thorium atoms, and all Thorium isotopes are radioactive.

04-25-2019, 11:20 AM   #47
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QuoteOriginally posted by mccririck Quote
regarding the banana K-40 makes up 0.012% of potassium atoms.

Th-232 makes up 99.98% of Thorium atoms, and all Thorium isotopes are radioactive.
Which should tell you that potassium is more radioactive than thorium since eating 1 banana was stated as being as bad, radiation exposure wise, as using a lens with thorium glass for an hour. Neither are very hot given that potassium 40 has a half life of around 1.2 billion years while thorium has a half life of about 14 billion years and the longer the half life the lower the emissions over a given time. I would guess that the damage from radiation is greater from the banana as it is taken internally and decays exclusively through beta decay while the thorium from the lens is mostly alpha decays and is external and blocked by lots of stuff.
04-25-2019, 11:45 AM   #48
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QuoteOriginally posted by MossyRocks Quote
Which should tell you that potassium is more radioactive than thorium since eating 1 banana was stated as being as bad, radiation exposure wise, as using a lens with thorium glass for an hour. Neither are very hot given that potassium 40 has a half life of around 1.2 billion years while thorium has a half life of about 14 billion years and the longer the half life the lower the emissions over a given time. I would guess that the damage from radiation is greater from the banana as it is taken internally and decays exclusively through beta decay while the thorium from the lens is mostly alpha decays and is external and blocked by lots of stuff.
I'm not convinced. Hold a geyger counter next to a pealed banana and then at the front or rear of a radioactive lens.

Thoriated glass - Wikipedia


- Thoriated glass can contain up to 30% Thorium by mass.


- average banana peeled weighs 116g. Of that 334mg is Potassium. 0.334/116 x 100 = 0.29%

So there is 100 times more Thorium in the glass than Potassium in a banana, and nearly 10,000 times more radioactive isotopes in Thorium than Potassium.


As well as that there are several beta decays in the Thorium decay series:

04-25-2019, 01:50 PM   #49
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QuoteOriginally posted by mccririck Quote
I'm not convinced. Hold a geyger counter next to a pealed banana and then at the front or rear of a radioactive lens.

Thoriated glass - Wikipedia


- Thoriated glass can contain up to 30% Thorium by mass.


- average banana peeled weighs 116g. Of that 334mg is Potassium. 0.334/116 x 100 = 0.29%

So there is 100 times more Thorium in the glass than Potassium in a banana, and nearly 10,000 times more radioactive isotopes in Thorium than Potassium.


As well as that there are several beta decays in the Thorium decay series:
The difference is from the effects of ingesting a radioactive chemical versus exposure to a radioactive object at a distance. With the banana, 100% of that radioactivity is deposited inside your cells where it can wreak the greatest damage. With the lens, most of the radiation is emitted pointing away from the body, is absorbed by other materials between the disintegrating thorium atom and the body, or emitted when you body is not near the lens. Time, shielding, and distance means that very little of the lens' radiation gets into you.

04-25-2019, 01:56 PM   #50
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QuoteOriginally posted by photoptimist Quote
The difference is from the effects of ingesting a radioactive chemical versus exposure to a radioactive object at a distance. With the banana, 100% of that radioactivity is deposited inside your cells where it can wreak the greatest damage. With the lens, most of the radiation is emitted pointing away from the body, is absorbed by other materials between the disintegrating thorium atom and the body, or emitted when you body is not near the lens. Time, shielding, and distance means that very little of the lens' radiation gets into you.
Well, as I've pointed out, beta radiation is present in the Thorium decay, and it goes through skin. If you watch the angry photographer video on youtube with the highly radioactive Kodak lens, it goes through his hand, and through some copper sheeting. Try doing that with a banana. There is far less radioactivity in a banana for the reasons I have already stated.
04-25-2019, 02:30 PM - 1 Like   #51
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I think you are getting a bit confused. It isn't 30% thorium it is 30% thorium dioxide. Also it isn't the total lens weight but the weight of the radioactive element or elements and even there the only one you need to be concerned about is the outer most one as all the alpha particles will all be stopped from the any elements not on the outside (remember an alpha particle is huge in this context) and most if not all of the beta particles will also be blocked from any radioactive inner elements. The other interesting thing is that a radioactive element like thorium is actually a pretty good blocker of radiation as it has that nice dense big nucleus that has a higher probability of stopping those awful gamma and x rays but most of those will still escape the lens and most of those that go your direction will go through you like you weren't there too.

So if we assume that the rear radioactive element weights in at 10 grams, seems like a reasonable good guess considering that the 50mm Super Takumar f/1.4 weighs in at 230g, that means that 3 grams of that is thorium dioxide. Of that 3 grams of thorium dioxide .41 grams are oxygen and 2.59 are thorium. Now since we want to know how many radioactive atoms there are we need to convert things to moles using their atomic weight which is also the weight in grams of 1 mole of that element. This would give us about .011 moles of thorium or about 6.624x10^21 atoms of thorium. In your banana there would be about .0001 moles of radioactive potassium, or 6.022x10^19 atoms. So that 10 gram rear radioactive element has about 100 times more radioactive atoms in it than that banana does, not the 10,000 times you claim but those radioactive atoms in the rear lens element do weigh a lot more but that doesn't really matter. While we are dealing with 2 orders of magnitude difference in the numbers of radioactive atoms half life still plays an important role, and in this case that potassium 40 (a half life of 1.2 billion years) in the banana is over 10x (an order of magnitude) as active as the thorium (a half life of 14 billion years). So I would expect the lens to register about 10 times the number of emissions over the same period of times as the banana, but the lens will mostly be alpha emissions and they will all be outside of your person while the banana will all be beta emissions and if you eat it will all be internal where they can do the most damage.

So I stand by my assertion that the radiation from eating a banana is likely more damaging than the radiation from a camera lens with thorium glass.
04-25-2019, 03:06 PM   #52
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QuoteOriginally posted by mccririck Quote
Well, as I've pointed out, beta radiation is present in the Thorium decay, and it goes through skin. If you watch the angry photographer video on youtube with the highly radioactive Kodak lens, it goes through his hand, and through some copper sheeting. Try doing that with a banana. There is far less radioactivity in a banana for the reasons I have already stated.
That may be true but the calculations for radiation dosage (as calculated in Sieverts) compensates for that.

Ironically, if the radiation is making it through your hand, it actually means it's doing less damage to your flesh because it means that the particles are coming out the other side with much of their energy intact.

P.S. The potassium in bananas (and other things) is a beta and gamma emitter.
04-25-2019, 03:26 PM   #53
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QuoteOriginally posted by photoptimist Quote
P.S. The potassium in bananas (and other things) is a beta and gamma emitter.
P.S. the Thorium decay in lenses is an alpha, beta and gamma emitter. (Yes there is some gamma too, in the same way as potassium. And the Thorium decay series is longer than potassium - there are more steps.

As for the person who commented that it is Thorium dioxide used in lenses. Well that makes only a small difference to the calculation since the atomic weight of Thorium is 232 and the atomic weight of oxygen is only 16.

04-25-2019, 03:47 PM   #54
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QuoteOriginally posted by mccririck Quote
P.S. the Thorium decay in lenses is an alpha, beta and gamma emitter. (Yes there is some gamma too, in the same way as potassium. And the Thorium decay series is longer than potassium - there are more steps.

As for the person who commented that it is Thorium dioxide used in lenses. Well that makes only a small difference to the calculation since the atomic weight of Thorium is 232 and the atomic weight of oxygen is only 16.
The decay chain of Thorium (and it's 10 daughter products) does not make as big an impact on the risk as does the ingestion of the banana. Radiation emitted inside your body does more damage than radiation emitted outside at a distance.
04-25-2019, 04:29 PM   #55
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QuoteOriginally posted by photoptimist Quote
The decay chain of Thorium (and it's 10 daughter products) does not make as big an impact on the risk as does the ingestion of the banana. Radiation emitted inside your body does more damage than radiation emitted outside at a distance.
Pretty strong statement. Define "distance".

BTW...ingestion of the banana has net ZERO impact.


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04-25-2019, 04:49 PM   #56
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QuoteOriginally posted by stevebrot Quote
Pretty strong statement. Define "distance".

BTW...ingestion of the banana has net ZERO impact.


Steve
"Distance" would be the physical distance between the disintegrating nucleus and living tissue. For the case of the ingested banana it is zero because the potassium is absorbed into the body. No matter which direction the emitted potassium-40 radiation flies, it hits living tissue. For the case of the lens, it's some number of centimeters during lens use and probably meters during storage. Most of the radiation from the thorium or daughter products flies off harmlessly away from the photographer and much of the radiation that flies toward the photographer must pass through the rest fo the lens, shutter, sensor, circuit board, back panel, and then dead skin to get to living tissue.
04-25-2019, 05:51 PM - 1 Like   #57
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QuoteOriginally posted by photoptimist Quote
For the case of the ingested banana it is zero because the potassium is absorbed into the body. No matter which direction the emitted potassium-40 radiation flies, it hits living tissue.
The banana is a red herring. Eating it neither increases nor decreases the risk of tissue damage due to radiation. In fact, total abstinence from bananas will not change things either.

Distance with regards to gamma is important because it is simply extremely short wavelength light (EM radiation) and obeys the inverse square law. Gamma penetrates flesh quite easily and has potential to change matter that it passes through. The color change of our lens glass is probably the most accessible example of what thorium in that concentration can do. In theory, similar mischief might be done to genetic material much the same as with UV light. Without actually doing measurements with a scintillation detector, it is hard to say how much gamma is absorbed by passage through the back of the camera or whether the remnants are energetic enough to be a risk to the lens' user.

I am only noting these things because they illustrate that concern about the thorium-doped glass is not silly or particularly irrational any more than concern about dental and other x-rays are silly or irrational. What we can say with some certainty runs like this:
  • No obvious pattern of disease has been noted within the ranks of prominent photographers who regularly used the more strongly radioactive Ektar lenses
  • While thoriated lenses will fog photographic film, it takes a fairly long period of time, even with the film in close proximity
  • A more common source of radioactive thorium exposure familiar to many of us who went camping in our youth are the silk mantles used for gas lights and lanterns. Don't breath or eat the broken mantle dust! Now they tell me...
This short list as well as a few other points has led me to treat my "hot" lenses much the same as I do a UV lamp. Unless there is a clear reason to do so, I avoid basking in its rays. I also avoid lingering in the crawlspace under my house...radon...


Steve

Last edited by stevebrot; 04-25-2019 at 05:57 PM.
04-25-2019, 06:22 PM - 1 Like   #58
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QuoteOriginally posted by stevebrot Quote
The banana is a red herring. Eating it neither increases nor decreases the risk of tissue damage due to radiation. In fact, total abstinence from bananas will not change things either.

Distance with regards to gamma is important because it is simply extremely short wavelength light (EM radiation) and obeys the inverse square law. Gamma penetrates flesh quite easily and has potential to change matter that it passes through. The color change of our lens glass is probably the most accessible example of what thorium in that concentration can do. In theory, similar mischief might be done to genetic material much the same as with UV light. Without actually doing measurements with a scintillation detector, it is hard to say how much gamma is absorbed by passage through the back of the camera or whether the remnants are energetic enough to be a risk to the lens' user.

I am only noting these things because they illustrate that concern about the thorium-doped glass is not silly or particularly irrational any more than concern about dental and other x-rays are silly or irrational. What we can say with some certainty runs like this:
  • No obvious pattern of disease has been noted within the ranks of prominent photographers who regularly used the more strongly radioactive Ektar lenses
  • While thoriated lenses will fog photographic film, it takes a fairly long period of time, even with the film in close proximity
  • A more common source of radioactive thorium exposure familiar to many of us who went camping in our youth are the silk mantles used for gas lights and lanterns. Don't breath or eat the broken mantle dust! Now they tell me...
This short list as well as a few other points has led me to treat my "hot" lenses much the same as I do a UV lamp. Unless there is a clear reason to do so, I avoid basking in its rays. I also avoid lingering in the crawlspace under my house...radon...


Steve
As I said before, it is wise to be worry about voluntary exposure to radiation whether it is a dental x-ray, flight across the country, granite countertops, visits to or living at higher altitude, or using an old Takumar lens. Each of these comes with some risk from radiation and the wise person attempts to quantify it to make an informed choice. What is foolish is to over-estimate the risk to the detriment of other things in life (e.g., flying is a great way to get to photographic opportunities or dental x-rays help prevent more serious problems).

The banana example merely serves to show the ubiquity of radiation in the natural world and provides a convenient measuring stick for exposure doses. If the amount of radiation associated with the potassium in one banana is not a concern (and the human body continuously stores about 500 bananas of potassium), then another source of exposure equivalent to one banana isn't a significant worry, either, but the exposure might become a concern if it is multiplied a 1000X (e.g., eating a Takumar lens).

Last edited by photoptimist; 04-25-2019 at 06:34 PM.
04-25-2019, 08:14 PM   #59
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QuoteOriginally posted by mccririck Quote
I guess the important thing is not to look into the lens close up. Don't hold it up to your eye and stare into it!

Has anyone measure the radiation from the front of the lens, from the rear, from the sides, and then from the rear when it is attached to a camera? It would be interesting to see the differences.
Here's a scientific study that explains how small the level of radiation from an average thoriated lens is: http://www.diva-portal.org/smash/get/diva2:652338/FULLTEXT01.pdf

This topic has, of course, been beaten to death in this forum over the years. See, for instance:
Radioaktiv Lenses - PentaxForums.com
Or; throium glass lenses - PentaxForums.com


If you were to spend a thousand hours per year looking through your camera lens (that's 2.73 hours per day, every day of the year, or, 19.23 hours per week) you would be exposed to a total of 0.2 mSv/yr. That is the equivalent of about 5 or 6 intercontinental flights a year or 2 chest x-rays. One CT-scan is 20mSv, so you'd have to look through your lens for 10,000 hours (There's 8,760 hours in a year) to get the equivalent exposure as to one CT-scan.

Your normal background radiation exposure, in the USA, averages 6.24 mSv per year. If you use your lens for 24 minutes every day, your annual exposure would increase by about 0.5%.
Put another way: If you have granite benches in your kitchen, your annual exposure will be somewhere between 0.005 to 0.18 mSv depending on the type of granite, if you spend 4 hours a day in the Kitchen. It could be argued that going outside and taking photos will be safer for you than spending time in your kitchen.
04-26-2019, 03:49 AM   #60
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I'm not saying it is extremely dangerous. I was taking issue with some of the statements you made which were not really true.
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