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  1. #1

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    Keeping film longer with lead?

    A recent thread in the large format forum asked what would happen if the two big manufacturers of color film (Fuji and Kodak) both stopped producing film. The general theme running through the answers seemed to be "don't worry about the sky falling" and "stock up while you can".

    This has led me to think about options for stacking up. Refrigeration slows down the deterioration of the emulsion (I'm guessing that this occurs because chemical reactions slow down under lower temperatures) but film still gets fogged over time, and I remember reading in a Kodak data sheet that this occurs as a result of stray radiation hitting the emulsion. So, the question is: has anyone tried storing film long-term inside, say, lead bags of the sort sold to protect film from x-ray machines? It seems you could keep film fresh much longer by freezing it inside a lead box or one of these types of bags.

    If you've tried this or you have a good reason to think it won't work, please let me know.

    Thanks,
    Melchi
    Melchi M. Michel

  2. #2
    David A. Goldfarb's Avatar
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    I don't think it will help much. Cosmic rays, which fog film over a long period of time, pass through the Earth.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
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  3. #3

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    My feezer shelves are groaning under the weight as it is. Lead boxes would crush it :-)

    David.

  4. #4

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    Quote Originally Posted by Woolliscroft
    My feezer shelves are groaning under the weight as it is. Lead boxes would crush it :-)

    David.
    Well, it seems polyethylene (as in Mylar) might also be effective. http://science.nasa.gov/headlines/y2...spaceships.htm
    This might be a more managable solution.
    Melchi M. Michel

  5. #5

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    The only cosmic ray component that passes through the Earth is neutrinos. But you don't have to worry about them fogging your film because they also pass through your film.

    The radiation environment in space is very different than on the surface of the Earth. The primary cosmic rays contain energetic charged particles such as protons and heavier nuclei. These are hard to stop with shielding without producing additional radiation, hence the idea of polyethylene for a Mars mission. These primary particles never reach the surface of the Earth because of the Earth's magnetic field and atmosphere (otherwise we would be dead or have a very high rate of cancer). Plastic is not a good shielding material for the secondary cosmic rays at ground level, nor for the radiation from natural radioactive isotopes.

    Lead is a good shielding material. But it is expensive. More of a cheaper material might be more cost effective. The film shield bags are rather thin -- they are designed to block low-energy x-rays. Thicker lead or some other material like thicker steel might work better.

    I remember reading that for long-term storage of film, Kodak uses an old salt mine. The most penetrating cosmic ray component (ignoring the neutrinos, which are so weakly interacting that they don't matter) are the muons. It takes tens of meters of material to block muons, so a mine is a good approach -- obviously out-of-scope for putting in your freezer. But not any mine will do -- granite or similar rocks are likely to contain uranium or thorium, and so will contribute a background radioactivity.

    So, yes, shielding will probably help extend the lifetime of frozen film against fogging, but I don't know whether the lead bags sold to shield film from airport x-ray machines are thick enough to make much difference.

  6. #6

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    You not only have cosmic rays but also background radiation which comes from the soil. Years ago when I was doing research we used a double layer of lead bricks to reduce background radiation. A lead brick is about the same size as an ordinary clay brick. In other words, you would need a lot of lead to do any good.

    Fortunately, most of the fog comes from heat and is reduced by freezing.



 

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