Nikon AI Lenses and Radioactivity

markjwyatt said:

Thorium 232 produces an alpha particle, but the resulting decay product may produce gamma radiation.

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Exactly. And these typically are measured (unless you git a counter with high transparency for alpha-radiation) and this raduiation is harnfull from the outside too.

markjwyatt said:

It is listed, but I am not sure it is correct. A lot of Kodak amateur cameras at that time used radioactive lenses.

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I never ever came across any Ektar lens, thus with Ektar I always think of those Gauss types...

Russia knows about radiation, and they dont mind any rats giving 4 headed babies after they sleep wtih their owners camera lens.

Whats the old adage about lead paint? dont put it in your mouth.

Bronson Dugnutt said:

It's tough to balance the sensor sensitivity required to detect an event and the inherent noise in a long exposure. Too low a sensitivity and particles won't be registered unless lots happen to strike the same photosite. Examining sensor (non?) performance in this way is a fun way to evaluate a digital camera, but ultimately illustrates why film is a better solution for very long exposures.

Here's an extreme crop from a 60s blackout exposure on a V2 w/ Nikkor 35mm f1.4 via FT1. There are a few 'hot' pixels but I don't have any baseline to compare against; the rear element of the lens was the full F flange distance (46.5mm) from a 1" sensor so YMMV.

View attachment 290310 View attachment 290309

(RAW and RAW w/ post noise reduction)

Downright... astronomical.

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I won't talk about the pros and cons of film vs digital for pictorial long exposures - it would be tedious and also off-topic since this is in a film forum. As you allude to, digital sensors run at room temperature have a significant pattern noise due to dark current. For strictly measurement non-pictorial purposes, it is helpful that digital sensors make it easy to subtract dark frames, which is necessary here. That's what the Nikon long exposure NR does, I'm not sure if it also does any noise spike removal (which would be a problem since that's what we are looking for).

Anyway, I tried this with manual dark subtraction (I turned long exposure NR of, and took a few dark frames and subtracted them myself). However, the results are inconclusive. I stuck a Nikon D100 in a changing bag with a test lens and took a pair of 30 sec exposures, then switched the lens, etc. I tried a couple of Nikon lenses, old Yashica and Mamiya M42 lenses, an Olympus 28/3.5, and a Kodak Signet. After subtracting darks, I wasn't able to see any sign of "cosmic ray" radiation hits. The camera did have some bias drift that affected the dark subtraction, and a later model DSLR would likely have lower noise. The real problem is that I don't have any test subjects that are verifiably radioactive lenses. Even the Kodak Signets, which make it onto these lists of thoriated lenses, show no sign of radiation browning, which is said to be common in some Super Takumars.

So I can't tell if this method is any use or not. I don't think the radiation from thoriated lenses is strong enough to be a problem (unless maybe you keep it in your pocket 12 hours a day or put it in your bed), so it's a little academic.

Bezoar said:

Russia knows about radiation, and they dont mind any rats giving 4 headed babies after they sleep wtih their owners camera lens.

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You are quite astray, as none of the soviet consumer lenses contained radioactive glass. Instead the majority known today were american and japanese.

Nitroplait said:

Yeah the reference in your source to is really convincing. I must revise my position.
Anyway; everything is radioactive to some degree. If you are worried, NEVER set foot on a airplane!

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Or live in Aberdeen. That's Aberdeen, Scotland by the way

pentaxuser

reddesert said:

So I can't tell if this method is any use or not. I don't think the radiation from thoriated lenses is strong enough to be a problem (unless maybe you keep it in your pocket 12 hours a day or put it in your bed), so it's a little academic.

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I think bremsstrahlung can be a problem. When the easily stoppable alpha or beta particle hits something heavy, conservation of energy requires it to convert its energy, often to something far more dangerous - a gamma particle/ray. Those are not easily stoppable, and can do some serious damage. If you have bad luck.

I've read that keeping the active object behind acrylic or aluminium can allow the particles to slow down, and reduce this type of radiation.

Would be interesting to hear if there are any physicists on the forum that knows something about bremsstrahlung.

Even with Bremsstrahlung aside, the decay series of Thorium produces both, Alpha and Gamma radiation.

There may be other sources of radiation in ones homes. But the only sources I found going over the stable radiation level inside and outside my home are my lenses.

AgX said:

Even with Bremsstrahlung aside, the decay series of Thorium produces both, Alpha and Gamma radiation.

There may be other sources of radiation in ones homes. But the only sources I found going over the stable radiation level inside and outside my home are my lenses.

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Try a banana.

Of course a banana will cause zero rise. You completely overestimate my/our metering equipment.

markjwyatt said:

Try a banana.

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My bananas have never been radioactive enough to give a reading.

Lenses though have been 60x the background radiation.

bananas

https://en.wikipedia.org/wiki/Banana_equivalent_dose

"One BED [Banana equivalent dose] is often correlated to 10−7 sievert (0.1 μSv); however, in practice, this dose is not cumulative"

OK, my lens was 60 BED then. Equivalent to eating 60 bananas per hour? Doesn't sound very healthy.

FotoD said:

Lenses though have been 60x the background radiation.

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I just took a reading at a radiating Dubble-Gauss lens at hand.
28x basic radiation. at front element
3x basic radiation ar rear element

This at best shows the influx of position the respective element(s). We even cannot deduce that a hot element was at the front.

And with my basic meter I even refrain to make a quantitative statement, though I could.

I asked one of my sons who is a nuclear physicist about the Canon 35mm f2 Thorium lens that I've owned for nearly forty years, he said " it doesn't emit a tenth of the radiation that's allowed annually to workers in the nuclear industry, and as long as you don't sleep with under your pllow dad you will be O.K, anyway at your age I wouldn't worry.

FotoD said:

I think bremsstrahlung can be a problem. When the easily stoppable alpha or beta particle hits something heavy, conservation of energy requires it to convert its energy, often to something far more dangerous - a gamma particle/ray. Those are not easily stoppable, and can do some serious damage. If you have bad luck.

I've read that keeping the active object behind acrylic or aluminium can allow the particles to slow down, and reduce this type of radiation.

Would be interesting to hear if there are any physicists on the forum that knows something about bremsstrahlung.

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I am a physicist, but I am not a health physicist, which is why I keep referring people to the Oak Ridge Museum of Radioactivity page at https://www.orau.org/health-physics.../products-containing-thorium/camera-lens.html , because that page is written by a health physicist with a strong historical interest in these issues. Other websites of interest include https://www.epa.gov/radiation/radionuclide-basics-thorium and https://www.epa.gov/radiation/calculate-your-radiation-dose and the NRC's NUREG-1717 report section 3.19 on the exemption for "Thorium in finished optical lenses": https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1717/index.html

To give a baseline comparison, the Oak Ridge page reports a calculation (from the NRC's NUREG-1717) that a "serious" photographer carrying a camera with a lens containing thorium for 30 days x 6 hours/day, might receive an annual exposure of 2 millirem. (The more extreme example would be a person using a thoriated glass eyepiece for long periods at work, such as a TV cameraman, but thoriated glasses in eyepieces seem to be rare and I doubt there are many TV cameras left from the time when thoriated glass was in use). This includes all the products of the decay chain, betas, gammas and so on. For comparison an ordinary person's annual exposure is of order 100-200 millirem - see the EPA calculator linked above. 2 mrem is the exposure from flying 2000 miles on an airplane.

This is why I keep saying that these lenses ought to be safe but don't store them under or next to your bed. The proximity and duration of exposure matter.

The danger of radiation depends on activity, energy, and proximity. The worst thing is if you swallow or breathe the radioactive element (why eg radon gas is bad). Fortunately in camera lenses the thorium is solidly encased in glass. Thorium mantles for camping lanterns could lead to more exposure, although even there I think the real problem is for the workers who made the mantles.

Thorium has an extremely long half life which is why it is still around. That means its activity is relatively low (decays per second) so even though it emits some betas and gammas, the rate of exposure is small.

Bremsstrahlung ("braking radiation") is the production of X-rays when energetic electrons (betas) are scattered, in this case off atomic nuclei. Heavier elements produce more intense bremsstrahlung, I believe because the heavier nucleus has less recoil and the electron is decelerated more quickly. The wiki page on bremsstrahlung gives the example of phosphorus-32 and the (counter-intuitive) need to shield it with a thick layer of light material rather than a thinner layer of lead. But there are a couple of reasons why this isn't a general concern. First, phosphorus-32 is extremely active: it has a half-life of 14 days (vs thorium-232 at 14 billion years) - the activity of 32P is ~300 tera-Becquerel per millimol (a few tens of milligrams) vs camera lenses measured at ~10 kilo-Becquerel (from NUREG-1717). Second, both betas and X-rays are absorbed/scattered by a reasonable thickness of ordinary materials, perhaps a meter of air for beta rays, solid material for X-rays. Despite Superman, you can't really see through a wall with X-rays. Anyway, I'm pretty sure this effect is minor for thorium and that it is taken into account by actual health physics analyses.

Anyone with a strong interest/concern in the subject should read NUREG-1717 section 3.19 carefully: https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1717/index.html

As with other cases, the high risc is for those making the glass, grinding the glass or being in contact with the grinding waste. The latter can be third persons, in no way related to photography and optics.

AgX said:

As with other cases, the high risc is for those making the glass, grinding the glass or being in contact with the grinding waste. The latter can be third persons, in no way related to photography and optics.

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Probably the biggest risk is to those grinding teh thorium oxide, and/or mixing it into the melt.

Kodak got a problem once their dumped grinding waste was found.

By the time Nikon Ai lenses came out the Japanese health and safety executive had banned the use of radio active materials in lenses several years before in Japan, mainly because of the danger to workers of grinding the lens elements and ingesting the dust, not because of any danger to the public.

markjwyatt said:

Probably the biggest risk is to those grinding teh thorium oxide, and/or mixing it into the melt.

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I read something years back, that the main hazard with Thorium was in the grinding and polishing of the glass in the factory. The fine dust stayed in the air, not exactly the best for those who worked in a lens plant.

Jim B.

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