Thorium glass - how bad is it?

[MNS]

Greetings,

I came across a video on YouTube on Fuji Fujinon 55mm f2.2 Lens radioactivity and I have a copy of the lens which in the test has the strongest reading from a Geiger counter.

I'm pretty shocked as the lens elements don't look yellow and I was unaware of Thorium glass being in this lens.



In the video my lens version gives a reading of 11266 to 11315 CPM. Looking online it says anything above 10,000 CPM typically indicating significant exposure. 😱

Should avoid handling too much or just not worry about it?



M.

​

 

[titrisol]

How bad meaning?
Thorium glass was amazing optically!

Most of the radiation is harmless, and I dont see than lens here

https://camera-wiki.org/wiki/Radioactive_lenses

 

[valdas]

If you don’t seep with this lens under your pillow and don’t hold it close to you for hours each day - nothing to worry about. That is my coclusion after reading various articles on this subjec written by science people.

 

[MNS]

Think that list is not complete.

Camerapedia - Radioactive lenses

As far as I can now tell as long as I don't hold the lens to my eye or lower parts of my anatomy it shouldn't too much of an issue.

 

[willie_901]

It's not bad.

Thorium-232 (the only naturally occurring isotope) emits alpha particles during decay. Since alpha particles are large, they rapidly dissipate energy when passing through gases, liquids and solids. In air, alpha particles cannot penetrate more than 3 cm. In solids their penetration is thousands of time less.

Normal lens usage is not risky. Just keep it in a case or on the camera. Your largest exposure should be during cleaning the lens elements. It turns out ingesting alpha particles while breathing is unhealthy since the radiation is concentrated in a small volume of tissue. I wouldn't put the front or rear of the lens closer than 10 CM to my face during cleaning.

Alpha decay is low radiation energy process. A piece of paper can block alpha radiation. When the lens is on the camera, the camera body blocks the radiation, as does the lens body. Off the camera a rear lens cap will block alpha particles. The glass in a UV filter will block radiation from the front of a front lens element as will a lens cap. When the lens in a case the expose will be low.

Thorium decays to Radium-228. Radium-228's half-life is less than 6 years.

It turns out it's possible to calculate the ratio of Th:Ra isotopes during radioactive decay. Fortunately 1 gram of Th-232 produces 4 x 10^-7 grams of Radium-228.

Normal lens usage is not risky. Just keep it in a case as much as possible.

Your largest exposure should be during cleaning the lens elements. It turns out ingesting alpha particles while breathing is unhealthy since the radiation concentrated in a small volume of tissue during radioactive decay. I wouldn't put the front or rear of the lens closer than 10 cm to my face during cleaning.

I wouldn't use the lens without a clear, high-quality UV filter. A front lens caps reduces inhalation risk in the rare event that shatters the front lens element. It would be unhealthy to breathe in glass-dust debris.

 

[valdas]

 

[MNS]

Funny enough @valdas I've just watched Simon's utak series on the subject.

 

[MNS]

The only reason this all come about was because I was think of using this camera (I've never used the Fujica before, I pick it up for next to nothing some years ago) and was curious about the Fujinon 55mm lens and the images it's capable of producing.

Having seen the video (listed above) then finding it on the Camerapedia - Radioactive lenses list as well, I was a tad shocked. I always thought it was older lenses effected and many of them the glass has a yellow tint. I'm obviously misinformed and didn't realise how many lenses even into the 1970s use this glass and lanthanum.

Now with further reading I now understand the reasons and benefits of using Thorium in optics regarding lens design and refractive index.

Thankfully, I'm pretty certain it's the only radioactive lens I own and in my late father's little collection.



So, I will be using the Fujica but from a distance. With arms out stretched in front of me, wearing a hi-vis jacket and radiation warning stickers stuck all over the camera

...health and safety you know! 😂

 

[boojum]

OK, let's cut to the chase. If that Thorium radiation were serious it would probably fog the film. Has this happened?

 

[MNS]

OK, let's cut to the chase. If that Thorium radiation were serious it would probably fog the film. Has this happened?

That was the other point that puzzled me. Although, I think it might be interesting using a changing bag to place a Thorium lens onto a small film strip and develop it to see if there's is any effect.

 

[Muggins]

The only reason this all come about was because I was think of using this camera (I've never used the Fujica before, I pick it up for next to nothing some years ago) and was curious about the Fujinon 55mm lens and the images it's capable of producing.

Having seen the video (listed above) then finding it on the Camerapedia - Radioactive lenses list as well, I was a tad shocked. I always thought it was older lenses effected and many of them the glass has a yellow tint. I'm obviously misinformed and didn't realise how many lenses even into the 1970s use this glass and lanthanum.

Now with further reading I now understand the reasons and benefits of using Thorium in optics regarding lens design and refractive index.

Thankfully, I'm pretty certain it's the only radioactive lens I own and in my late father's little collection.

View attachment 4877343

So, I will be using the Fujica but from a distance. With arms out stretched in front of me, wearing a hi-vis jacket and radiation warning stickers stuck all over the camera

...health and safety you know! 😂

A small collection, but beautifully presented! And some very nice cameras too.

 

[p.giannakis]

Most lens manufacturers used thoriated elements to correct optical aberrations. They are not dangerous unless you break the glass and thorium is inhaled or digested. Some isotopes emit gamma radiation but levels are low. You cannot put too much thorium dioxide in the optical mix as instead of optical glass you get ceramic, so radiation is relatively small.

The Pancolars are probably the worst of the bunch - instead of one thoriated element (usually placed at the end of the lens) they used 4. The front element of the pancolar is as close as it gets to radioactive element.



There are some large format lenses made by Ross which are not safe to use. These are very rare though.

👉 Do you want to know what is more dangerous? Thoriated eyepieces.

Yes, you read it well. If you have a Canon FX, a Nikkormat FTn, a Pentax SV, a Yashica Electro and others , the eyepiece just next to your eye might be thoriated. Thorium is in small amounts in those eyepiece but still there and your eye ball is the next thing near it. I wouldn't worry much about them though.

External eyepieces are the real danger - Kodak offered eyepieces with 30% thorium in them - for sure there is some sort of eye cancer hidding there. I think Nikon did the same for the F. If you get an external finder and is yellow - don't use it.

 

[Freakscene]

That was the other point that puzzled me. Although, I think it might be interesting using a changing bag to place a Thorium lens onto a small film strip and develop it to see if there's is any effect.

Somewhere I have a photo ‘exposed’ by putting a Pentax 50mm f1.4 Super Takumar with a thorium element on top of the film sheet for a few days in a darkroom and then developed. I think I needed to use Royal-X Pan to get it to work, showing that there is hardly any meaningful radiation. I had to work out which element was radioactive to know what end to point at the film. Even the thorium eyepieces are not really that dangerous unless you grind them up and swallow or breathe them in.

Marty (radiation safety officer at several workplaces over a few decades)

 

[p.giannakis]

I always thought it was older lenses effected and many of them the glass has a yellow tint.

That is correct in most cases but not always. Just because a lens is radioactive, it doesn't mean that it will yellow. It needs to be exposed to light for a significant time to yellow.

Sounds counterintuitive as sunlight cures the yellowing but it is not. If a lens receives enough sunlight to trigger yellowing but not enough to cure it (Like in most cases), then it will continue to yellow until is exposed to enough UV to tip the balance towards clearing again.

My view is that your lens saw very little use, always had a cap on and was stored inside a case, therefore never received enough UV light to trigger a significant yellowing process.

Edit:
Or the previous owner cleared it.

 

[MNS]

My view is that your lens saw very little use, always had a cap on and was stored inside a case, therefore never received enough UV light to trigger a significant yellowing process.

I will agree with that. When I purchased the Fujica was in it's semi hard case with it's original lens cap. Once opened it become pretty obvious the camera had little use through it's life. There was little or no dust through the viewfinder or the 55mm lens. Other than that, there was the usual seal degradation and the common Fujinon lens problem of a cracked plastic focusing ring.

I was charged the extortionate sum of £2.00 ($2.69) for the camera from a house clearance store back in 2009.

 

[joe bosak]

I bought a geiger counter after I found about about this a few years ago. My finding was that 80mm Biometar and a 50mm Flektagon were significantly radioactive, producing at least 10x background radiation in a plume still detectably very high several feet away and through the leather case, lens caps, layers of tinfoil and a plastic box. That seemed more like gamma radiation to me, presumably from decay products. I think it was from the fronts rather than rears of the lenses, but either way: in a domestic setting, it made me think you need to be careful about where you store them.

 

[p.giannakis]

I bought a geiger counter after I found about about this a few years ago. My finding was that 80mm Biometar and a 50mm Flektagon were significantly radioactive, producing at least 10x background radiation in a plume still detectably very high several feet away and through the leather case, lens caps, layers of tinfoil and a plastic box. That seemed more like gamma radiation to me, presumably from decay products. I think it was from the fronts rather than rears of the lenses, but either way: in a domestic setting, it made me think you need to be careful about where you store them.

Yes, health and safety was not a priority in East Germany at that time. A friend of mine who used to work in Heriot-Watt University in Edinburgh, in the physics department, measured both my takumar 50f/1.4 and 55f/1.8 and said it was low and no cause for worry. East German lenses might be a different case though.

 

[MNS]

Yes, health and safety was not a priority in East Germany at that time.

...only personal health and safety regarding arrest by the Stasi I should imagine. 😆

 

[santino]

I think that night vision devices were much worse. Regarding lenses and hazardous radiation, It is a never ending story full of speculations. Truth is that most lenses can be used safely. Who knows what emits potentially dangerous radiation in your household? I personally don‘t have a Geiger counter…

 

[titrisol]

OK, let's cut to the chase. If that Thorium radiation were serious it would probably fog the film. Has this happened?

not really
please see the radiation articles by Gerjan van Oosten and
the study by KTH (sweden) : https://www.diva-portal.org/smash/get/diva2:652338/FULLTEXT01.pdf
and the US Army: https://www.irpa.net/irpa3/cdrom/VOL.3B/W3B_13.PDF

Glass browns under radiation, as observed by the U of Chicago lab in the 1940s (where Fermi experimented) and can be cured with intense light or UV as shon in this study: Effects of ionizing radiation on selected optical materials: An overview (Technical Report) | OSTI.GOV