P67 RADIOACTIVE thorium-containing (thoriated) lenses

I have just found that my Pentax 67 normal lens from 1972, the Super

Takumar 6x7 105mm f2.4 (Asahi Optical Co.) is thorium-containing and

therefore radioactive. Have a look at this list of thorium-

containing lenses from the 1970s:

<http://www.orau.org/ptp/collection/consumer%

20products/cameralens.htm>

 

 

Interesting enough, the British Ministry of Defence has issued some

guidelines about how to deal with thorium-containing (thoriated)

lenses at: <www.mod.uk/linked_files/dsef/hp/jsp392/pdf/chap47.pdf>.

I have copied them for your info.

 

 

Thoriated Lenses

 

 

4723. There are currently two types of thoriated lens in use. These

are the thorium fluoride coated germanium lens and the homogeneous

thorium oxide lens. The coated lens can present an internal hazard if

the coating is damaged leading to the possibility of ingestium of

throrium. The hazard from the homogeneous lens is principally an

external radiation dose to the eye.

 

 

4724. Equipments containing thorium lenses are also to be marked with

a radiation warning sign unless this is not possible for operational

or other safety reasons.

 

 

4725. In applications where thoriated lenses are placed close to the

eye, they are to be replaced with a non-thoriated substitute where

operationally acceptable or where modification of the equipment is

undertaken, a plain glass shield is to be introduced between the lens

and the eye.

 

 

4726. Spare

 

 

4727. In all locations where equipment containing thoriated lenses

are maintained a clean-up kit is to be readily available. In the

event of breakage or flaking of a lens the same clean up procedure is

to be followed as for broken radioactive valves described in Annex

30A, and disposed of in accordance with paragraphs 4748-53.

 

 

4728. Glass fragments entering the skin are to be removed immediately

(where necessary by the medical officer) and the wound cleaned under

running water. The incident is then to be reported to the medical

officer. The RPA is also to be informed at the earliest opportunity

if it is suspected that any fragments remain within the wound.

 

 

 

From the information on the two websites, I have undertood that

INGESTION OF (radioactive) THORIUM IS A MAYOR DANGER FOR THE

PHOTOGRAPHER. Therefore, as of today, I will always have the lens

with a UV filter and the hood on to make sure that it does not break

or loses some thorium material with a tiny scratch. Probably, I will

also clean it very carefully, wash my hands after cleaning it and

throw to the garbage the cloth.

 

 

However, it is the explanation of the fist website about the

estimation of the doses of radiation received from a photographer

using these lense that has left me with the question about whether

there is danger of radioactive exposure to the body or the eye. (I am

a lawyer and completly ignorant about radiation limits,etc.) Can

anybody help with the following text? My understanding is that the

danger of radiation from the Pentax 67 105/2.4 lens is really minimal

but that there is a extreamly high danger to the eye from using any

thoriated eyepiece in a camera. Can anybody with some scientific

background please tell me if I am wrong?

 

 

 

Dose Estimates

 

 

Perhaps the greatest health concern is the potential for thoriated

glass to be used in an eyepiece. This is not permitted by the

regulations, but it has occurred. If the eye is positioned close to a

thoriated eyepiece, the dose to the eye?s outer tissues can be

substantial. Casarett et al, assuming that an individual used an

eyepiece containing 16% thorium for 20 hours per week, estimated a

dose of 44 rad at a depth of 50 um, and 18 rad at a depth of 60 um.

Given a quality factor of 20, this would equate to 880 rem and 360

rem per year respectively. Similar calculations by McMillan and

Horne were in general agreement with these numbers. One measurement,

as opposed to a theoretical calculation, indicated a dose rate of

approximately 1 mrad/hr at the surface of an eyepiece containing 18%

thorium.

 

 

 

NUREG-1717 estimated that the dose to the operator of a television

camera using thoriated lenses could be as much as 60 mrem per year.

This assumed that three of the camera?s lenses contained 30% by

weight thorium and that the camera man was positioned behind the

camera for 1000 hours per year. Nevertheless, there is no evidence to

suggest that thoriated lenses are commonly used in television cameras.

 

 

 

Measurements have indicated that the exposure rate at a depth of 10

cm in the body of an individual carrying a camera containing 0.36 uCi

of thorium would be approximately 0.01 mrem/hr. Based on this value,

NUREG-1717 calculated that a serious photographer might receive an

annual exposure of 2 mrem. This assumed that the photographer carried

the camera 30 days per year and for 6 hours per day. They also

estimated an exposure of 0.7 mrem per year for an average

photographer. If the camera lens contained the maximum permitted

concentration of thorium (30%), NUREG-1717 estimated that the

aforementioned annual doses could triple.

 

 

 

Finally, FYI I want to add this link to the website of the Health

Physics Society dealing with thorium lense and how to solve the

problem of the colored reddish-brown lenses:

<http://hps.org/publicinformation/ate/q1215.html>

Canon introduced an FD mount Canon Thorium 35mm f2 Chrome Nose in the 70's.<P>The glass is yellow enough that it is considered unusable for color slides.<P>Many knowledgeable Canon B&W shooters feel this is one of the best lenses ever made as it's contrast seems to be better with it's "built in yellow filter".<P>About 10 years ago Roger Hicks wrote an article in Shutterbug magazine about Thorium. I'm sure copies are still around.

Can't answer for the Pentax lenses but out of curiosity I put a radiation monitor up against my Leica thorium glass tonight: Elmar 135 f4 and Elmarit 90 f2.8

There was no detectable emission whatsoever. Background cosmic radiation gives a click every five seconds or so and my luminous watch face sent the meter full scale deflection when held close up. I would not worry over this.

What year/ serial numbers of the 105 used this? I have one from around 1974, and it does look yellow when looking through it. How can you tell?

"Don't worry, be happy now!" :-) I have a half dozen lenses from among the ones listed, of the correct vintage to contain Thorium glass. But none of these carry the radiation caution symbol. I'd think, if there is any danger, that employees of the glass-maker, lens-maker, importer, and dealers would be at hazard. Never heard of any warnings.

 

Worth remembering that we have an on-going nuclear reaction irradiating us every day -- that bright thing up there in the sky. Good comment about the background cosmic rays too, and the Radium on watch faces, not to mention that radioactive elements occur naturally around us. We're used to it, but of course we don't want to get dangerous levels. If the levels of ionizing radiation in the lens glass are low enough not to fog the film for the time film is ordinarily loaded in the camera, then I think there's no health concern either.

 

Scott, if your lens looks yellowish, that's the test. Not a yellow surface reflection though, as that's just the coating. Look through the lens at a white piece of paper, also comparing the paper's color as it appears past the outside of the lens. If by comparison, the paper looks more yellow through the lens than past it, then that's the indication the lens has been affected by self-irradiation as mentioned in a previous post.

Scott as it has been mentioned here it is sure that your lens contains thorium. All the old Super Takumar 6x7 105mm f2.4 contain thorium. As long as you don't break it or scratch it everything should be OK. I am going to keep mine. The only danger with thorium are eyepices because the radiation is too close to the body (the eye is a few milimeters from an eyepiece) and ingestion of thorium. As long as you don't ingest thorium powder there is no real danger with thoriated lenses.

 

 

As for the danger that thorium lenses represent to workers, I guess that being thorium as nuclear fuel, the risk of processing thorium must be similar to processing uranium. If you take precautions you can process uranium, transport it and use it for many applications safely.

 

 

By the way, I have been told that nowadays thorium lenses cannot be manufactured in the EU because they no longer comply with European Law (blessed European Commission & Parliament if it were for some Member States we would eat thorium for dinner).

 

 

I attach a picture from someone showing a thoriated lens.

 

 

Seeing that, as long as you don't ingest thorium, the only danger are throriated eyepieces I wonder if you know of any. I have in mind the Albada finders of the Zeiss Ikon folder cameras for instance. They are known for getting a similar color to the color of thoriated lenses, could it be that they also contain throium?

My lens has a definate yellow tone to it when looking through the viewfinder. I always wondered why that was. If I knew the age of it I wouldnt have bought a lens that old for my 6x7.

Scott. This lenses are fantastic among other reasons because of the great coating made with thorium. For many people these thoriated lenses are the best of their time and much better than many modern lenses. The yellow comes out with the light of the sun or heat. Be careful that the oil in the lens does not go through the wrong places when you put the lens in the light of the sun. A lot of people has reported that after putting the lens in thw window with the British (not Mediterranean) sun, the yellow is gone. Although it seems that heat treatment is faster I assume that it means that you will also have to deal with the internal oil problems of the lens. If choose heat contact the people of the Health Physics Society who are the ones who say that heat is very effective. If you choose heat (disassembling the lens?) let us know the results as I have never seen anybody using the heat treatment yet.

The fact that a radiation (Giger presumably)counter doesn't pickup radioactivity may not ultimately be all that useful. Some decay particles only travel a few mm in air and others like gamma particles will pass right through a giger counter without being detected. For example Tritium cannot be detected by a giger counter even though it is radioactive. I'm afraid I can't tell you what particles thorium breaks down to, I'm sure we have some of those here that can.

If you search the archives, I think you will find an old posting about this very subject. Although I am not a nuclear chemist, a real nuclear chemist from some university wrote about the thorium in the glass, or thorium coatings. I will try to summarize his writing. 1. Thorium is an alpha emitter, that is the nucleus of a helium atom, and is short lived. 2. He wrote the funniest thing "Don't grind the glass up then SNORT IT!", that would coat the small sacks in the lungs with alpha emitters, other than that you should be O.K.

Gee! What's that glowing? Is that a Super Takumar 105 in your pants or are you just happy to see me? :-)

 

I'm sorry. All the exposure to the radio waves has fried my brain! . . . as opposed to all those pithers of beer & fixer fumes!

I think we've all missed something obvious here. If the glass does put out substantial radiation, then it would fog the film in the camera. -BC-

Bill. When it comes to radiation time and distance are very important variables. An experiment by Roger Hicks in his article proved that thoriated lenses do fog the film after some days in DIRECT contact with the lenses. I never had my film foged in my P67 because there are a few centimeters from the radioactive lens and film. However, I don't think I am going to leave film inside the camera for weeks from now on, just for precaution.

 

 

 

Because the issue is distance, the real danger comes from thoriated eyepieces and not lenses. Eyepieces are a just few milimeters from the eye. Lenses are not a direct danger because they are not close to the human body. However if you ingest thorium from your lens time and distance increases. Time: thorium will stay inside your body radiating. Distance: 0 milimeters, it will have direct contact with the tissues of your body. Therefore thoriated lenses are not dangerous at all, unless you ingest the material coating the lens. Thoriated eyepieces are always dangerous.

Frenando-- Wow. Thanks for all the good info. I'm thinking of getting a 6x7 system (been a Pentax 35mm SLR shooter since age ten), and I'll certainly take that thorium coating into account when looking at lenses.

 

As if we didn't have enough to worry about in dealing with deadbeat ad agencies, stressed-out brides, and clients who wonder why we don't do three or four extra days work on a project without charging any extra, now we have to worry about getting dosed by radiation.

Ok, it looks like there's virtually no danger from Thorium-glass lenses unless we smash 'em and let the shards enter our system, or chew on them, etc. And it seems that the larger concern should be with Thorium-glass eyepieces. So, which cameras have been made with such eyepieces, so that we may avoid them?

Doug, you are right. That is exactly the point. While thoriated lenses were legal until recently, the use of thorium in eyepieces both in the USA and in the European Union (Euroatom) became illegal pretty soon. (I do not know about Japan though). However, there are many records that despite the general prohibition some manufactures have used thoriated eyepieces. The links above mention the names of scientific authors who have recorded the existence of radioactive eyepieces that were manufactured violating the prohibition. The British MoD is also sure of their existence among their material, which is why it is asking for their substitution in their guidelines.

 

 

 

My personal view is that since Roger Hicks article in Shutterbug ten years ago, we photographers have been focusing too much on thoriated lenses, which are not really dangerous, and not in the eyepieces, which are the real danger. Therefore, photographers know of many lists of thoriated lenses now, but we have no clue about a list of radioactive eyepieces, which is the list we really need. Also, because so many radioactive eyepieces were manufactured violating the prohibition, I do not think many manufactures will be very happy to publish their immoral records about their old thoriated eyepieces. I guess they fear the damage to their image and potential litigation.

 

 

 

So, which ones? That is the question I am also posing. I have no clue. A few weeks ago I was wondering if the yellow/orange color of the albada viewfinders from the old postwar Zeiss folders might have something to do with this. Has anybody tested them?

first of all, if you place your lens close to your bed, that is a bit dangerous./ since you've got as short as six hours everynight.

<p>Thorium decays through a series of isotopes, some of which are gamma emitters. See http://www.csupomona.edu/~pbsiegel/decaychain/Th232.html for the decay chain. After a little under 9 years from when the thorium was originally purified you'll have a completely repopulated thorium decay chain present. </p>

<p>My Geiger counter responds to radioactive lenses, including Pentax 67 lenses, which should be impossible if they were only emitting alpha particles. The radiation will go right through sheet metal which also rules out beta particles as the cause for this response. It's gamma. On the plus side, with a little distance you can't detect any difference from background radiation. Just keep the lenses away from wherever you spend very much time, like your desk or bed.</p>