Radioactivity of old manual lenses

no-X

I prepared a test of radioactivity on majority of my lenses. Here is the result:

I made measurement for both rear and front elements (1cm distance, if possible). Some results are as expected, but some of them are a bit surprising for me:

S-M-C Macro Takumar 50/4: radioactive... VERY low intensity, but present. I think it uses lanthanum glass.

Super Takumar 35/2.0 V1 / PRO (the big one)... low radioactivity, half than on the later version, which is known to be thoriated... this level of radioactivity could mean utilization of lanthanum glass or very low amount of thorium

S-M-C Takumar 85/1.8: I have never seen this lens in any list of radioactive lenses, but its radioactivity is really evident. It's very untypical, that front side radiates more than the rear one, so the thoriated(?) element is located in front optical group...

Carl Zeiss Jena Biometar 80/2.8 (zebra, P6): next surprise... while the old M42 (alu) version isn't radioactive, the newer one (for medium format cameras) is. Radioactivity level is really low. It could be lanthanum glass or very low amount of thorium...

I made some colored highlights to allow easier orientation... blue = low radioactivity, red = high radioactivity

PaulC · Joined: 23 Dec 2008 Posts: 2318

Hey, cool! I might have a hot lens for my P6.

PS: The stability of your background radiation measurements is very impressive and certainly leaves little room for doubt about the accuracy of your results.

aleksanderpolo · Joined: 24 Jan 2010 Posts: 684

Thank you so much, yeah, my S-M-C Tak is first runnerup! Laughing

Joking aside, do you have experience of how long it takes to "de-yellow" the lens with UV treatment? I have been putting it behind a window glass under the sun for more than two weeks now.

no-X · Posted: Fri Feb 26, 2010 9:35 pm Post subject:

PaulC: I must say, that the results aren't 100% exact (cheap dosimeter, I have no idea, what aspects can impact the measurement etc., accuracy is at best 20nSv/h - very likely lower), but I think, that all colored results really stands for radioactive glass.

I also found informatio, that both thorium and lanthanum glasses were developed in time and it became so pure, that its radioactivity was almost non-existant. It means, that even non-radioactive lenses can be equipped by thorium/lanthanum elemens.

aleksanderpolo: As I remember, I used 11W UV tube and it took about 5 weeks for S-M-C 50/1.4...

Orio · Expire: 2012-12-04

thanks, very interesting !

It looks like all lenses, regardless of brand and model, have radioactivity levels higher than the background.

I wonder where does it come from - the glass? the coating? the barrel?

Another thing I'd be curious to see, is some test on today's autofocus lenses, to compare.

Which brand and model of detector did you use?

Orio · Expire: 2012-12-04

Another thing to consider:

if a normal "clean" lens averages around 180 radioactivity, a bag with 6 lenses (not that uncommon, considering that many of these old lenses are small) becomes a not so reassuring 1080 radioatcivity bag that you may carry all day near your abdomen or your lungs (depending on the type of bag).

Something to think about.

It also means that Carsten with his typical trekking setup of 15 or so lenses goes around with a little nuclear bomb hanging from his shoulders! Shocked

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no-X · Posted: Fri Feb 26, 2010 9:52 pm Post subject:

In fact some lenses slightly lowered the background radioactivity - mainly CCCP models (thick metal parts?).

I used the cheapest one I could get - Radex RD1503.

PaulC · Joined: 23 Dec 2008 Posts: 2318

Ooops! Didn't read the chart properly Embarassed

If we're going to go further we need to determine what kind of radiation you are getting before we start worrying about the cumulative lensing effects of it in Carsten's bag.

peterqd · Expire: 2014-01-04

Orio · Expire: 2012-12-04

No-X have you tried to measure your lens cabinet (assuming that you keep your lenses together in one place) at about say 1 mt distance - which would be the typical walking distance ?

lwsy711 · Joined: 21 Oct 2009 Posts: 230 Location: VA, US

Jiri,
Nice job!
Just want to know what is the distance you put your dosimeter away from the lens.
Thanks,
Wei

Orio · Expire: 2012-12-04

lwsy711 · Joined: 21 Oct 2009 Posts: 230 Location: VA, US

Orio · Expire: 2012-12-04

Sevo · Expire: 2012-12-03

Sevo · Expire: 2012-12-03

peterqd · Expire: 2014-01-04

Attila · Expire: 2025-11-18

Send me guys all dangerous lenses I will sleep with them LOL.

Orio · Expire: 2012-12-04

Sevo · Expire: 2012-12-03

There have been warnings regarding radioactive eyepieces on telescopes and rifle sights. Photographic lenses are harmless in use - for optical reasons, the thoriated element is never the front lens, so that the radioactivity (alpha, which does nor even reach far in air) is well contained. Scrapping them could prove expensive, though, and they aren't made anymore, as workplace safety regulations would be close to those in a nuclear plant.

no-X · Posted: Fri Feb 26, 2010 11:09 pm Post subject:

Sevo: Thanks

other data:

1m distance from my lens cabinet (closer to the place where are 35+50mm lenses): 200 nSv/h

similar measurement in another room: 170 nSv/h

S-M-C Takumar 50/1.4 (distance of rear element + result):

0 cm ~ 1740 nSv/h
5 cm ~ 630 nSv/h
10 cm ~ 420 nSv/h
20 cm ~ 280 nSv/h
40 cm ~ 180 nSv/h (similar level to normal background)

test repeated with rear-cap (plastic) on:

0 cm ~ 1460 nSv/h
5 cm ~ 620 nSv/h
10 cm ~ 310 nSv/h
20 cm ~ 210 nSv/h
40 cm ~ 180 nSv/h (similar level to normal background)

Takumar + both caps + soft lens case + piece of cloth between lens and dosimeter + 10cm distance (to simulate carying the lens in photo-bag): 330 nSv/h

I'm not a physicis, but I think that means, that during a 3-hour trip with Takumar you'll get as much radiation as on 5-hour trip without it(?)

So... if you won't store the Takumar under your bed (or less than 40cm to your body), it shouldn't affect you...

Orio · Expire: 2012-12-04

peterqd · Expire: 2014-01-04

Orio · Expire: 2012-12-04

PaulC · Joined: 23 Dec 2008 Posts: 2318

The effect of radiation isn't cumulative, the chances of it affecting you are.

You're talking about whether a high energy particle happens to knock a bit of your DNA about. If a collision (or miss) doesn't do damage then it doesn't increase the risk of the next collision doing damage. If you walk away from the source before it damages you, then you should be OK.

However, if you increase the number of collisions five-fold then you have five times the chance of getting one that is damaging.

But this also means that the first collision might be the one that does the harm .... or you might get lucky and have n-billion that don't hurt you.

The risk that the first particle might just be the harmful one is the reason there is not a safe level for radiation. It's not the same as a chemical poison where a certain dosage is always harmless and a certain overdose always lethal.