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Should I be worried about these lenses? Radioactive? Help.


pensacolaphoto

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Michael,

In your opinion, is the Trivision camera of some value ?

Could it be adapted for "standard" photography or is it too specialized for practical use?

I really like this camera, but when I bought it, I wanted to have it modified for portrait photography. I never did.

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Dear Roger,

I think you are right about "Jack" being the correct person.

I will continue my search for more information on how the military made use of the Trivision 3D camera. What type of film was used in the early 40's to require a max aperture of 1.66 and for which applications?

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Don't forget lanthanum, a rare earth metal used in lighting and obviously where the name Lanthar comes from. There are 23 radioactive isotopes of this element in addition to the 25 stable isotopes.

 

Radioactivity is a relative term. Stick your dosimeter under a dental x-ray camera for a second, and compare the reading to what you get off your lens overnight. You will be frightened of the dentist's office the next time you go.

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<p>Attributing the radioactivity to Lanthanum is a common misconception that I discuss in my <a href="http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html">Aero-Ektar webpage</a>.

Only two of the dozens of isotopes of Lanthanum are pertinant: natural Lanthanum is composed of 99.9098% La-139 and 0.0902% La-138 (see La isotopes at <a href="http://ie.lbl.gov/education/parent/La_iso.htm">http://ie.lbl.gov/education/parent/La_iso.htm</a>).

The common isotope La-139 is stable; La-138 is radioactive with a half-life of 100 billion years (100,000,000,000). The trace amounts of La-138 in naturally occuring Lanthanum and its extremely long half-life means that the radioactivity of naturally occuring Lanthanum is extremely low. In comparison, 100% of naturally occuring Thorium is the radioactive isotope Th-232, which has a half-life of 1.4 billion years (<a href="http://ie.lbl.gov/education/parent/Th_iso.htm">http://ie.lbl.gov/education/parent/Th_iso.htm</a>).</p>

 

<p>If you want another element for radioactivity, try Potassium (<a href="http://ie.lbl.gov/education/parent/K_iso.htm">http://ie.lbl.gov/education/parent/K_iso.htm</a>).

Natural Potassium contains 0.0117% of the isotope K-40, which is radioactive with a half-life of 1.3 billion years. But avoiding lenses containing Potassium won't accomplish much since the human body contains 0.4% Potassium by weight (<a href="http://www.daviddarling.info/encyclopedia/E/elbio.html">http://www.daviddarling.info/encyclopedia/E/elbio.html</a>).</p>

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  • 3 weeks later...

Most Geiger counters have a sound-mode in which they make clicks everytime they detect a high-energy radiation. The first step is to turn on the Geiger counter away from the lenses, at least a few meters distance, and get a feel for the rate of clicks from the background radiation. You might want to write down the background reading, if the counter is sensitive enough to give a non-zero reading. Then bring the meter up close to the lens and see if the click rate goes way up. That's the exciting part.

 

For the careful part, I suggest writing down your measurements. Be sure to record what kind of meter you used, the size of the window area of the probe, how far away it was from the lens, what the units on the scale were, which part of the lens was closest, etc. For accuracy, have only one lens near the Geiger counter and keep the others distant. You might want to figure out which portion (front/back/sides) is most radioactive.

 

You might want to see how far you have to move the counter away from the lens until you can't detect an increase above the background late.

Another experiment would be to try various materials as shielding, e.g., thin cardboard, sheet meter, a brick.

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Raid; most of the Radioactive Ektars I have are "hotter" towards then rear. Makes a sketch; and measure the meters readings versus distance. You can make the sketch beforehand; and just record your numbers direcly on a full scale drawing. This is how I have plotted magnetic leakage of devices; and radioactive stuff too. <BR><BR>Check some oddball glasswear too. I found none; a buddy had some. As mentioned above; My 1970's vintage unused Coleman lantern mantels were radioactive; and in the desk right by my computer. My hot lenses were in two rooms away.<BR><BR>The meter I used had a test patch; and a chart that gave the cal factor by year. <BR><BR>I found some of my Kodak Printing Ektars were radioactive; a 113mm Ektar.
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Hi,

Today I picked up an old portable Geiger counter from the Physics dept. at the university where I work. The newer counters were not protabale I was told. Anyways, it is a OCDM CD V-700 Model No. 6 Geiger counter by Anton Electronics Labs. It has a check source built in to calibrate the instrument. It works as it is suppoed to. I was told that this instrument is used to measure Gamma rays but not Beta rays. Dose equivalent: unit is rem and not rad, I was told.

The counter has three settings:1X, 10X, and 100X, allowing readings from 0 to 0.5 mr/hr for 1X

0 to 5 mr/hour for 10X

0 to 50mr/hour for 100X.

It should be noted that the built in material in the Geiger counter reads 0.2mr, so it should be OK for the people using the counter.

Outside the camera room, the reading is about 0. It never is at exactly 0. I measured the smaller lenses, and there was no response from the counter. As I got closer to the "big lens", the counter started to move. The highest dose was measured at 0.5mr when placing the sensor flat against the middle of the camera where the lens elements are. It is at about 0.02mr/hr at 1.5 yards from the camera and about 0.2 mr/hr at 12 inches from the camera. There is no response at 2 yards from the camera.

What do you think guys? Should I donate the camera to science and stay away from it?

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<p>For what it is worth, US regulations allow radiation exposure to members of the public of up to 100 mrem per year. See <a href="http://www.nrc.gov/what-we-do/radiation/sources.html">http://www.nrc.gov/what-we-do/radiation/sources.html</a>, which states towards the bottom: "<i> Above this background level of radiation exposure, the NRC requires that its licensees limit maximum radiation exposure to individual members of the public to 100 mrem (1 mSv) per year, and limit occupational radiation exposure to adults working with radioactive material to 5,000mrem (50 mSv) per year.</i>" The regulation is stated at <a href="http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1301.html">http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1301.html</a>.</p>

 

<p>If you stood with the closest part of your body 1.5 yards from the camera, your peak dose rate would be 0.02 mrem/hour. The regulation probably implicitly assumes a whole body does -- we can overestimte that whole body does by using 0.02 mrem/hour for your entire body and not just the portion that close to the camera. With your measurement and this assumption, you would receive the legal yearly maximum dose (excluding radiation workers and patients) in 100 / 0.02 = 5000 hours. So you have have to spend more than half of each day this close to the camera to reach the 100 mrem limit.</p>

 

<p>Another way would be to estimate your does by how many hours per day you think you might be this close to the camera and compare to the background dose. For example, if you spend 1 hour per day near the camera, your dose per year would be 0.02 mrem/hour X 365 hours = 7 mrem. The typical dose from background sources is about 360 mrem per year (see the first link above), so this example case would represent a 2% increase in your exposure.</p>

 

<p>Of course, the dose rate would be up to 0.5 mrem/hour if you touched the camera, but it isn't realistic to imagine that you would spend much time doing this.</p>

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Michael,

I thank you again for your indepth postings on the issue of radioactive lenses and their potential effect on us. Your calculations have reassured me that "I'm fine". Still, I have decided to donate the camera and three lenses to my university (physics department). They will have the camera on the top floor (away from people most of the time) for potential use as a telescope. No clue how they will do it.

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