X-ray and Film Fogging

f16sunshine

f16sunshine

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I'm arranging to have some IR film posted from Germany and the question came up again about x-ray damage. A question that comes up all the time I know.
After flipping through dozens of google pages with a few different queries I have no answer to the following....

Why does an X-ray scan at 10nm fog a film that is sensitive between 400nm-680nm?
 
As obvious as it sounds, surely it must depend on the scanner... whether it be airport luggage/carry-on/shipping/land shipping/lorry scanner/ etc etc im sure they all must vary in their xray output.

just as an aside, i see 2 out of 80 rolls a day on average at the lab i work in that have x-ray damage, from countries all over the world.

varying iso's from 100-3200 ive seen all damaged with sine-wave style xray markings, then only 800 and above from fog/enhanced grain issues, of course this is hardly a scientific survey!
 
Silver halides are sensitive from the lower frequency of their sensitization up, without any (practical) limit (see e.g. http://www.cdags.org/dagforum/topic.php?id=138 for a Daguerrotype plate spectrum, i.e. a pure silver iodide deposit on a silver plate). There is some drop in the UV band which is soon caught up, and from then on sensitivity increases proportionally to the energy up to the point where wave lengths get near sub-molecular scale (where the probability of hitting into and interacting with a molecule decreases). By the X-ray range, sensitivity actually is at fairly low levels (X-rays mostly manage to get past even dense substrates like steel), so that dedicated X-ray film has to employ some x-ray luminescent intensifier layer or sandwiched sheet - but if a X-ray photon hits, there is no doubt it will expose the crystal.

Film has additional banding in ranges where the substrate (gelatin or base material) is opaque, and there may be some odd luminescence phenomena that create a few further zigzags, but essentially, there is no "between", only a "from".
 
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The sensitivity of the film extends further into the shorter wavelengths. That's why you can use Quartz glass to do UV photography with regular film.
 
Thank you all for your responses.

I see that my thinking was blocked. The range of sensitivity I'm used to looking at in charts is only in the area of visible light for humans. So in reality, the emulsion is sensitive much lower than the 400nm we can see. Thus, the potential for fogging.... so simple.
 
f16sunshine said:
The range of sensitivity I'm used to looking at in charts is only in the area of visible light for humans.
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And that which common lenses are transparent to - most types of glass used in common lenses are opaque to most of the UV range (and beyond), so that film manufacturers usually do not bother to specify the UV response except for technical films likely to be used with dedicated UV lenses (made from fluorite or special glasses).
 
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Peter Wijninga said:
Germany, probably OK but not so in dozens of other countries... 'it fogs because x-ray machines are not maintained'.
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It is primarily the question of maintenance that Peter refers to that causes me to not allow my film to be x-rayed. I also know there is an effect from just one pass although it may not be noticeable to most but the effect is cumulative. I do not wish to keep track of how many times each roll has been through the x-ray machine.

I am now 16 for 16 in avoiding x-ray in Cuba where it is mandated. My average time there to convince them to allow me to pass without x-ray of my film is about 15 minutes. Longest is just over an hour.

But everyone should feel free to allow their film to pass through the x-ray if that is their choice. It is just not mine.
 
X-Ray machines for hold luggage are very different to those for hand luggage. The former will fog your film; the latter should not unless it is high speed film or very many passes.

I have probably had a hundred scans on film over the last five years years and not seen ill effects.

Regarding nimcod's observations, I would level a bet that the vast majority, if not all, went through hold baggage scanners.

I have had 400 speed films, Neopan 1600 etc scanned 8,9 times or so and all fine. I have had D3200 scanned at least once and fine. Sure I try to avoid scans where possible, but sometimes it isn't possible. Dubai airport staff can range from helpful to utter shi**s, but that's because they don't know anything about their own equipment and care about your film less than they care about their own professionalism. I have had to capitulate and scan the film, but thankfully it has all been OK so far.

My personal method is to calculate how many passes I expect. As long as it is less than the threshold of 6 passes or so, I ask for a hand search and if I don't get one within about ten mins I go through the scanner. this tends to mean that I only get 2-3 scans of my film these days. I'm just not interested in fighting beyond this because it does not seem to matter.

As for poor maintenance leading fogging, I have heard this is an urban legend and that machines can only really output within a certain tolerance no matter how well or badly they are serviced. Make sense I suppose. Your 100 hp car does not suddenly put of 600 hp because it did not get a filter change!
 
Turtle said:
....................... As for poor maintenance leading fogging, I have heard this is an urban legend and that machines can only really output within a certain tolerance no matter how well or badly they are serviced. Make sense I suppose. Your 100 hp car does not suddenly put of 600 hp because it did not get a filter change!
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My situation may be unique but I am avoiding x-ray in a country where about 1/3 of the cars have engines different from the original manufacturer. If I could be convinced that the x-ray tube in the scanner was identical to the one originally installed by the manufacturer, I would not be so concerned.

Again, if you feel comfortable having your film x-rayed, that is fine with me. When I spend two weeks of time and significant expense to travel specifically to photograph, I simply want to take no chances.
 
Sure, thats understandable and my images are equally valuable to me, but the below is not typical of international airports around much of the world (although I daresay some come close). As you say, it is a personal choice, but that's a separate matter to the evidence out there regarding carry on scanners and fogging of film. I too try to avoid the scanners, but I also have seen no firm evidence of fogging (with a few scans) aside from when people put film in their hold luggage.

I'd be surprised if you could pop the guts of a hold baggage scanner into a carry rapidscan or the like - I'd expect the components to be a bit more specialised than that - but I could be wrong.

FWIW I have had film scanned plenty of times in Afghanistan with the worst looking, most beaten (and likely least maintained) machines I have ever seen and never a problem. Maintenance? I don't think so! That money gets embezzled long before it goes anywhere near a maintenance program.

I agree, however, that scans are always best avoided.

Bob Michaels said:
My situation may be unique but I am avoiding x-ray in a country where about 1/3 of the cars have engines different from the original manufacturer. If I could be convinced that the x-ray tube in the scanner was identical to the one originally installed by the manufacturer, I would not be so concerned.

Again, if you feel comfortable having your film x-rayed, that is fine with me. When I spend two weeks of time and significant expense to travel specifically to photograph, I simply want to take no chances.
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The risk carry-on scanners pose to film has diminished, and the risks involved in hand inspection are growing. Personally I rather scan the film and be done with it than risk that the (usually not film-aware, and often generally dim) inspectors open film loaded cameras or magazines or proceed to unroll all my exposed film.
 
Went on one trip through the middle east where my 3200 asa film must have been xrayed 15 - 20 times, no problems at all.

That would lend me to think that the internet has played a large role in this myth.
 
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