Radiocron

[HuubL]

A couple of years ago we had a short thread here about the radioactive Summicron. Someone there mentioned that the alpha radiation coming of an early version Summicron is no more than you get in a concrete building, but in my opinion it is considerable.

I decided to measure it with a GM counter in our lab. This link has a couple of pictures that speak for themselves.

1. background radiation: 2 cps
2. 3 cm from the front glass: 70 cps
3. on top of the front glass: 300 cps
4 & 5. the lead container I keep my lens in 🙂

As a molecular biology scientist I'm used to work with radioactive tracers, and counts like this make me pretty cautious when handling them.

 

[raydm6]

Yikes! 😱

 

[mfogiel]

So, to make this useful: for how many days would I need to keep this lens on top of my head to risk health issues?

 

[Mr_Flibble]

300 CPS is 18000cpm = 150 microSievert per hour

6 milliSievert = Average Annual Dose.

it would take 40 hours.

750 milliSievert = Radiation Sickness Dose

That would take 5000 hours. (208+ Days)

3000 milliSievert = Radiation Poisoning Dose

That would take 20000 hours (833+ Days)

Of course the chances of getting cancer increase significantly too.

 

[mfogiel]

Hmm, considering that HCB shot with THIS LENS ONLY most of his life, and he died at 96 either he was shooting through a lead shield ( hypothesis not confirmed by his rich archives), or in practical use this radioactivity is irrelevant.

 

[Mr_Flibble]

The camera would've shielded his body 😉

 

[michaelphoto]

If it really was so bad, would't it have ruined the film?

 

[ABrosig]

According to the folks at Oak Ridge lab https://orise.orau.gov/reacts/guide/alpha.htm, Alpha radiation (1) can not penetrate the skin, and (2) materials emitting alpha radiation can be very harmful only if ingested, inhaled or absorbed through an open wound.

I, personally, wouldn't worry about it.

 

[Rob-F]

According to the folks at Oak Ridge lab https://orise.orau.gov/reacts/guide/alpha.htm, Alpha radiation (1) can not penetrate the skin, and (2) materials emitting alpha radiation can be very harmful only if ingested, inhaled or absorbed through an open wound.

I, personally, wouldn't worry about it.

In my early 20' I worked for an AEC contractor (EG&G) at the nuclear facility in Nevada. I learned that alpha can only travel 2.5 inches from the source. Of course, when we handle or shoot with our radioactive Summicrons, we may be that close, or close enough not to argue the difference. When the camera is held up to the eye, for instance. On the other hand, there are seven glass elements and the camera body acting as a shield. I guess I don't worry about it either. I'll go with the HCB theory.

 

[x-ray]

Huubl I have a degree in microbiology and chemistry too but have always worked as a pj and commercial photographer. I worked it Oak Ridge National Lab (ORNL) in 74 & 75. In the 50's I grew up in Oak Ridge and my father was a nuclear designer / engineer.

One of my commercial clients for the past 25 years is Oak Ridge Associated Universities. Dr Paul Frame at ORAU has a museum, unfortunately not open to the public, of radioactive items from the late 1800's through the 70's. I know Paul through business and have photographed him on several occasions. He's quite proud of his collection and showed me many of the items in it. In that collection is a radioactive Pentax lens. His comment to me was that it contained low levels of Thorium but was of no concern.

I haven't seen Paul for a while but think he's still at ORAU. I'd suggest emailing or even calling him if you have concerns as he's quite a nice person and would be happy to give your information. The U.S. government has a public information office in Oak Ridge TN and can send information as well. You migh also contact someone in the physics department at your local university or even a radiologist or radiation oncologist.

From my knowledge and experience if there was significant radiation your film would be fogged over time especially 400 and 1600 ISO. Have you ever heard of fogged film from these lenses.

Look up alpha radiation. Alpha only travels a few centimeters and is absorbed / stopped by air. A sheet of printer paper will stop it as well and doesn't penetrate skin to any degree. Alpha is of most concern if ingested or inhaled. Particles emitting alpha in the lungs or bone can be very dangerous over time. In the case of lenses I certainly would not worry unless you inhale one or swallow it. ;-D

By the way old radium dial watches emitted alpha and gamma. I have one from the 1940's that's quite radioactive. I wore it to one of my shoots for a company that manufactures items from depleted uranium and had them check it for level. Even through the metal back it was very "hot" but of no danger. I can tell you from trying this it will expose 400 ISO film over night if placed in contact with it. I did a test by putting my film in a black plastic film bag and the watch on it. The gamma decay was high enough in 24 hours to make an image on the film.

Dont worry.

 

[HuubL]

Thanks x-ray,
I'm know that alpha emission travels only short distances through air and can effectively be stopped by a thin layer of denser material. That's indeed the reason why with a lens on a camera it won't effect the film. However, I was surprised to see that such a lens counts a lot, In any case when compared to the beta radiation that we normally use in probes in our experiments. In this case low emission like 50-100 cps results in exposed x-ray film to such levels that it leaves totally black areas on the film within a couple of hours. Of course, beta radiation travels much farther trough air or materials, but still, I was amazed by the severely clicking counter.

BTW, anybody noticed the missing screws in the LTM mount. There is a replacement screw, but that doesn't fit well. If you know of a source for such screws, please let me know.

 

[Saganich]

The alphas will not escape the glass. This is a natural thorium impurity in the lanthanum sourced for the glass. I ran a spectrum on an MCA and it is perfect match to natural thorium. Same as lantern mantel. As such the radiation consists of Thorium 231 mostly low energy conversion electrons, beta and gamma; not much dose rate. Most of the dose rate comes from the lead daughter Pb212 with a nice 238keV gamma. When mounted on the Leica the brass is enough shielding to attenuate a little over 90% of the Pb gamma. The dose rate on the front is about 6 to 8 mrem/hr on mine and drops to background at 20cm. The dose to the shooter is negligible. I keep mine in a 2mm lead lines stainless steel box since it's near my film stash and I don't typically leave it too long on a loaded camera.