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  1. #21

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    Quote Originally Posted by Photo Engineer View Post
    It may have been a cave.
    PE
    More Tongue in Cheek?

    Tell us about Batavia.
    Be free of all deception, Be safe from bodily harm
    Love without exception, Be a saint in any form
    (Patti Smith)

  2. #22

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    Quote Originally Posted by wiltw View Post
    Kodak had an article about accumulation of cosmic rays. Cosmic rays penetrate freezers, so while freezing might slow color shift in films, it will not do much to slow accumulation of cosmic radiation.

    Cosmic rays are resultant from our own sun and other stars. Cosmic rays originate outside our solar system. They consist of ionizing particles such as electrons, and atomic nuclei and non-ionizing particles such as gamma rays (photons), and neutrinos. Nuclei from every element and nearly every isotope are found.
    The most common of these are hydrogen (protons), and helium nuclei. Those nuclei formed in stars, such as carbon through iron, are the next most abundant.

    As for lead, I just found this description in a NASA publication about the methods used to shield a detector from cosmic rays,
    "Passive shielding is used to stop low-energy cosmic rays before they hit the CZT detectors. EXIST uses layered sheets of lead (Pb), tin (Sn) and copper (Cu). This layered approach is called "Graded-Z" shielding, which refers to the order and atomic number (Z) of those metals (Z equals 82 for lead, 50 for tin, and 29 for copper). Materials with larger Z have greater stopping power, and lead is used for the outermost layer. When a low-energy cosmic ray hits the lead it will be absorbed and ionize a lead atom which then emits an X-ray at the "characteristic energy" of lead, 88 keV, in a random direction. Lead does not absorb its own X-rays very well, so to prevent any of those X-rays from getting through the shielding, a layer of tin comes next. After absorbing the 88-keV X-ray, the tin may then emit a 29-keV X-ray. A layer of copper comes last. The few copper X-rays that reach the CZT detector are too low in energy (9 keV) to cause a problem. "

    So simple lead alone is insufficient, as it is necessary to shield from the secondary radiation byproducts that result from the cosmic rays striking the lead, too!
    Rubbish -it's the Lepracauns
    Mark Layne
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  3. #23
    Europan's Avatar
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    Ahm, heavy water, deuterium oxide, not natural water

  4. #24
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    Quote Originally Posted by Ray Rogers View Post
    More Tongue in Cheek?

    Tell us about Batavia.
    Ray;

    There are salt mines in this area, but are sometimes subject to flooding. There are caves out west used for storage. Kodak, to my knowledge, has used both at one time or another, but not for product storage.

    PE

  5. #25
    cmacd123's Avatar
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    heavy water is radioactive anyway.

  6. #26
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    When heavy water is used, it is as primary coolant and a neutron moderator, not as a radiation shield...and no, heavy water is not radioactive...though it is difficult to obtain in any worthwhile quantity, and completely unnecessary for shielding. Some plants use various forms of heavy water, but not the three I know, for various reasons (one reason simply being lack of necessity).

    Whether it is laced with other materials or not, or heavy water or not, water is not only one of the best radiation shields, but gives the highest linear attenuation coefficient ("squiggle") per dollar (by far!), and is readily available, harmless to us all, and presents zero problems in the way of disposal issues.

    The three plants I know obviously use the Rx vessel as the primary shield. No way to avoid that in any plant design. The secondary shield is a huge tank of water in all three designs, and it is plain-ol' water, for various reasons. It has a lower squiggle than metals, so is the widest layer of shielding. This is surrounded by a tertiary shield that is lead in all three cases. This cuts radiation inside the normally serviceable area of the Rx compartment to levels that are technically survivable even at operation...although atmospheric conditions in the compartment would not permit this, nor would Rx compartment entry procedures. Even so, the inner walls of the Rx compartment are lead lined. There are also small lead glass viewing windows (thick lead-impregnated glass that has a yellow tint).

    (Off topic, but FWIW, the primary source of exposure for plant operators is NOT radiation emanating directly from the Rx core. As I mentioned, this radiation is for all intents and purposes totally effectively (and fairly easily) shielded. It is radiation from beta decay of Co-60 (and subsequent gamma decay of the resultant Ni-60) carried out of the core by the primary coolant and lodged in low points of the primary system. Co-59 is found in valve seats and other wear areas of the plant, including, of course, the Nicor from which the primary plant is almost entirely constructed. As this wears, it is moved along by the primary coolant into the Rx core, where it can be blasted into Co-60. This Co-60 then finds itself settling in low areas or areas where stagnant pockets of coolant are prone to occur, and waiting to release a beta to stabilize. Unfortunately, by their nature, these areas are the areas that most often require service by humans. That is when the vast bulk of human exposure from nuclear plants actually occurs. On the plus side, if you have to get irradiated, betas aren't the worst possible thing by which to be irradiated. Unfortunately, the Ni-60 left over after the beta decay stabilizes by emitting gammas!)

    So, back to my idea...We would need to know the average types and doses of film-fogging radiation that film receives here on Earth, and I am sure that an effective shield could be designed when our beloved fast films are discontinued.
    Last edited by 2F/2F; 06-13-2009 at 03:24 AM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  7. #27

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    If cosmic rays are a significant cause of fogging it should be in the form of tracks (for rays traveling approximately parallel to the gel) or spots (for rays traveling approximately perpendicular to the gel.) Does old film show these kinds of structures in the fogging, or is it a uniform fogging? If it is uniform then cosmic rays are probably not a good explanation of the fogging.
    Last edited by alanrockwood; 06-13-2009 at 12:49 AM. Click to view previous post history. Reason: corrected punctuation error

  8. #28
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    Alan;

    Primary degradation is heat but yes, film does show rays and spots under close analysis. In fact, thick sheets of film are cast and used for this purpose by many agencies around the world. The film is exposed and then after suitable exposure and development as a thick "block" it is microtomed into thin wafers that are examined for such tracks.

    Nuclear explosion debris and cosmic rays can be individually accounted for using this method.

    I thought you knew this as a physicist / physical chemist.

    PE

  9. #29
    Nicholas Lindan's Avatar
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    Quote Originally Posted by alanrockwood View Post
    If cosmic rays are a significant cause of fogging it should be in the form of tracks [?]
    As I understand it the cosmic ray initiates a shower of secondary particles as soon as it hits the atmosphere. The initial ray is long gone by the time it gets here, or so we hope. A high-power "ray" packs the punch of a 100 mph baseball - quite a bit of energy for an atomic particle. If it hit the film directly it would be a very prominent 'track' - actually a hole, if it were to be a track then the ray would have to be coplanar with the film; the classic 'track' is a photograph of a particle's trajectory in a cloud chamber.

    What hits the film is likely a shower of soft x-rays. Over the years the radiation comes from all directions and fogs the film uniformly.

    Kodak stores it's stockpile of TMZ3200 deep in a salt mine.
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  10. #30
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    Kodak does not stockpile TMZ3200 in a salt mine.

    As for radiation sensitive emulsions, Kodak, Ilford and Fuji make a variety of liquid emulsions for sale that are used to either track the nuclear shower from above, or are made to just fog based on the background radiation level at any given time or place.

    Radiation sensitivity is not equated or equatable to visible light sensitivity in a direct linear fashion. Although higher speed films are more radiation sensitive, this is not a simple function of film speed. In some cases the level of heavy metal addenda, there for a variety of reassons, can alter sensitivity to quite an extent.

    PE

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