Why does unexposed film get fogged with age?

[2F/2F]

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.

 

[alanrockwood]

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.

 

[Photo Engineer]

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

 

[Nicholas Lindan]

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.

 

[Photo Engineer]

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

 

[alan doyle]

http://www.undergroundvaults.com/offerings/itemsstored/microfilmstorage.html
these saltmines do not look like they suffer from flooding.
so would you say in the last 30 years kodak has never stored unexposed hie or hir material in a saltmine...

 

[Photo Engineer]

Alan;

Please re-read my previous posts.

The vaults you refer to (and that I mentioned earlier) store records and contain PROCESSED films! They don't normally store raw stock in salt mines. As for flooding, the specific referenced salt mines in a post by Ray Rogers was a mine that had flooded within the last 20 years and was not used for this type of storage for just that reason. Among other things, the salt mines are too warm for raw stock storage.

PE

 

[alanrockwood]

Alan;

... 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...

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

PE

PE,

I knew that film has been used as a particle detector. That is why I asked the question about tracks and spots. It didn't make sense to me that cosmic rays are a major source normal age-related fogging. Otherwise I expect there would have been a lot of comments about the structure of the fog by users of old film, i.e. observation of tracks and spots in enlargements made from old film.

However, I did not know that emulsions were sometimes cast as blocks and microtomed as a method to find tracks. This is very interesting, but back to my original topic of tracks and spots on film, I am glad you have confirmed of my hypothesis about cosmic rays producing tracks and spots.

Picking up on your comment about emulsion blocks, I did a google search and found an interesting abstract on the topic: http://www.springerlink.com/content/l7800x1333168336/

On the topic of cosmic rays, at one time there was a cosmic ray observatory in the Utah desert known as the "flies eye". As I understand it this was basically an array of photomultiplier tubes, each pointing in a different direction toward the sky. When a cosmic ray passed overhead it would produce a light track in the sky. This was detected by the photomultiplier tubes, and the output of the array was made selective for cosmic ray tracks by looking at time-coincidences in several of the photomultiplier tubes.

Interestingly (to me at least, if not to anyone else) when I was a post doc at the University of Utah back in the early-to-mid 1980s I picked up an old surplus photomultiplier tube that was alleged to have come from the flies eye project. I carried it around for years in my various moves around the country. I may still have it, being the pack rat that I am, but I don't recall seeing it in any of my last moves, so I probably discarded it in one of my moves.

Concerning the comment by Nicholas that the fogging might be from secondary radiation (x-rays, or one might also mention gamma rays) caused by cosmic rays, this is a possibility, and I agree that this form of radiation would probably not produce tracks and spots because it is not as highly ionizing as charged-particle radiation. It would therefore not likely generate a strong track or spot in the film. What I am not sure about is whether the primary effect on stored film would be from electromagnetic radiation (x-rays or gamma rays) or from particles. Cosmic ray showers contain both.

 

[Photo Engineer]

Alan;

AFAIK, Konishiroku in Japan supplied the largest cast emulsion blocks and most of them went to a Canadian high altitude program that used baloon lofted blocks of emulsion. The processing and microtoming were done either at Konica labs in Hachioji or at one of the Tokyo universities.

They also had a fly eye setup which I visited in the 60s. It occupied a huge area in one building of the university, but I have forgotten which one.

You cannot equate x-ray, gamma and beta sensitivity in emulsions due to the energy difference. In fact, emulsions are sensitive to x-ray but not enough for practical use as they just fog and special fluorescent plates must be used to "focus" the energy into a usable image rather than a plain blur. At very high (damaging) levels of x-ray, then you do get sharp imaging.

As for Nicholas' comments about fogging from secondary radiation, this is undoubtedly a much bigger source of unwanted energy than direct impacts by the primary cosmic rays. But, the ones that do get through do leave tracks.

Incidentally, one impact was so energetic and of such a nature that it was believed to be a monopole. I never heard what came of that suspected incident.

PE

 

[Kirk Keyes]

PE - I hear that Orgone Energy is a major source of fogging in Super-XX film. ;^)

 

[Sal Santamaura]

...The vaults you refer to (and that I mentioned earlier) store records and contain PROCESSED films! They don't normally store raw stock in salt mines...Among other things, the salt mines are too warm for raw stock storage...

Ron, although fear of how high it must be has so far prevented me from contacting them for a price, Underground Vaults & Storage also offers refrigerated storage

http://www.undergroundvaults.com/offerings/securestoragefacilities/refrigeratedstorage.cfm

in a limestone mine 150 feet below the surface of Kansas City. While promoted for safe keeping of processed movie films, I don't see why it couldn't solve the cosmic radiation problem with long-term storage of higher speed raw stock.

I've recently "discovered" the beauty of sheet 320 TXP. Since Kodak supplies it sealed (under controlled humidity conditions) in a laminated envelope, why would there be any problem storing a lifetime supply (for someone of my advanced years ) in this Underground Vaults & Storage facility? The important question is: how effective would 150 feet of limestone be at retarding cosmic ray fogging? I've asked one of my Physics PhD friends to research that, but he ran into lots of dead ends. Seems to be a really specialized field that only someone with Kodak connections has a chance of effectively probing.

I realize that, if Kodak ever does stop film production, Tri-X will likely be the last emulsion to go. However, given Kodak's superb record of providing early notification about such discontinuations, it would be nice to know what the real prospects for long-term, relatively fog-free storage might be.

Thanks in advance for anything you can "dig up."

 

[Photo Engineer]

Sal;

The site you refer to offers almost perfect conditions. The humidity is a bit low, but otherwise it looks good. IDK about the cost but remember that Kodak has a rotating stock and therefore limited but large storage lockers at a fixed temperature and humidity. Storage at 40 deg F is just about ideal, but I think that 50% RH is better than lower values. Final coating conditioning is usually 75F 50% and chilling is done later for long term storage.

PE

 

[Sal Santamaura]

...The site you refer to offers almost perfect conditions. The humidity is a bit low, but otherwise it looks good. IDK about the cost but remember that Kodak has a rotating stock and therefore limited but large storage lockers at a fixed temperature and humidity. Storage at 40 deg F is just about ideal, but I think that 50% RH is better than lower values. Final coating conditioning is usually 75F 50% and chilling is done later for long term storage...

Thanks for that. I'd already concluded the same thing from a temp/RH perspective. The real question is cosmic radiation and how storage in this location would retard its fogging effect on 320TXP. If there's anything you can find out (at your convenience) concerning that aspect, I'd very much appreciate the information.

 

[Photo Engineer]

Heat death is more significant than radiation under most conditions.

PE

 

[stealthman_1]

I'm going to guess 2F/2F was a Navy ELT.
1/10th thickness is a term that relates to what thickness of a material is required to reduce a specific type of radiation to 1/10th the unshielded level. I'm straining my wine soaked brain here..., but IIRC, and that's a big if...for gamma rays, lead = 2 inches, steel = 4 inches and water = 12 inches, hence 2Fs comments about the economics of water. I have no idea the 1/10 thickness of limestone, but I'll bet it's not great, though 150 feet of it might offset its poor performance. If your local aquarium rents out space, your best bet would be a water tight container with liquid nitrogen refrigeration to -192 degrees F, suspended equidistant from all sides...Good luck with that.

 

[tony lockerbie]

Apparently the world is ending in 2012, so no point in getting film that is dated more than that!

 

[Sal Santamaura]

Heat death is more significant than radiation under most conditions.

PE

Understood, but attempting to keep 320TXP relatively unfogged for perhaps 30 years isn't "most conditions."

The real answer may be, as you implied above, that Kodak doesn't know either since it has had no reason to find out. If that's the case, I guess our best hope is crossing fingers that the product continues to be produced in coming decades.

 

[Kirk Keyes]

Heat death is more significant than radiation under most conditions.

Given this, perhaps you guys should think of getting a big liquid nitrogen dewer and start getting liquid nitrogen deliveries twice a week. Just remember to not drop the rolls while the film is still cold or it will shatter.

 

[2F/2F]

I'm going to guess 2F/2F was a Navy ELT.

Ah, YES! Tenth thickness is the exact term that I was trying to reach for in the depths of my irradiated mind...Thank you! No way in hell I can remember *every* bit of the crap that was shoved into our pea brains...though I could probably still draw fairly reasonable diagrams of the plants.

...and YES, those tenth thicknesses for gammas do ring a bell. I am almost certain that you are correct.

 

[BradS]

Apparently the world is ending in 2012, so no point in getting film that is dated more than that!

but, time runs out (or rolls over) in 2038.

 

[clayne]

but, time runs out (or rolls over) in 2038.

Everything before the 70s won't matter at that point - bring on the unsigned!

 

[Murray Kelly]

Is there any relationship to solar flares, which are non-existent at the moment (the cycle being next to dead at presently). What will happen over the next 5 years as the next cycle grows to maximum?
Murray

 

[Photo Engineer]

In the words of Tom Lehrer "we will all go together when we go!" I guess.



PE

 

[wogster]

but, time runs out (or rolls over) in 2038.

You would think after spending billions of dollars to fix the Y2K problem that they would now be dealing with 2038.

For those that do not know, many computer systems (including Windows) use the Unix date format, which counts the number of seconds since 12:00:00 AM January 1, 1970 as a signed 32bit integer which has a maximum of 2,147,483,647 values which means it runs out of values on January 19,2038 at 03:14:07 when the next value becomes -2,147,483,648 and computes to a date sometime in 1901.

The advantage to this system is it allows a date and time to be stored in 4 bytes, nice and compact, and it's easy to manipulate dates and times.

The problem is nearly every piece of computerized equipment that uses dates makes use of this, so everything from military satellites to iPods can be affected. Something like 99.999999999999999999999999% of all dates stored and used on the Internet are stored that way. Some software is now starting to be designed to use larger dates, commonly 64 bits wide, which allows a period in the past longer then the assumed age of the universe using the same methodology.

To be sensible you could allow for a finer granularity on time, for example the millisecond, and still cover a period of 58 million years.

Another possible solution is a sliding Epoch, for example if you advance the Epoch by 50 years, to 2020, you lose the ability to store dates prior to 1951, but gaining the ability to store dates to 2088. Because some future dates can be now stored, the problem needs to be dealt with within the next 10 years or so. Software using a sliding Epoch can use an extra small Epoch field, for example a single 1 byte unsigned field being the Epoch year less 1900 would allow a maximum date year of 2,223.

I suspect that a variety of solutions will end up being used.

 

[clayne]

Another possible solution is a sliding Epoch, for example if you advance the Epoch by 50 years, to 2020, you lose the ability to store dates prior to 1951, but gaining the ability to store dates to 2088. Because some future dates can be now stored, the problem needs to be dealt with within the next 10 years or so. Software using a sliding Epoch can use an extra small Epoch field, for example a single 1 byte unsigned field being the Epoch year less 1900 would allow a maximum date year of 2,223.

I suspect that a variety of solutions will end up being used.

I doubt it. We'll easily be using an uint64_t by the time we hit 2038. Y2038 is such a non-issue made into something seemingly important. There's also a huge difference in lead-time for this "problem" vs. Y2K and it won't even be a blip of any significance when 2038 rolls around.