Radiation fog damage to different ISO films from airport X-ray and CT security baggage machines and protection with X-ray shielding bags

1. Traditional X-ray machine vs. new Computed Tomography (CT) scanner

Undeveloped silver halide film is essentially a highly sensitive ionizing radiation recording medium that also has actinic reactions to X-rays and gamma rays other than visible light:

1. Traditional plane X-ray baggage machine (Cabin X-Ray):

• The irradiation dose is low (usually less than 1 microsievert/shot), and the cumulative damage to low-speed films of ISO 400 and below is weak in a single or even 2-3 passes.
• Produces irreversible slight ash lift and grain coarsening on ISO 800, ISO 1600, ISO 3200 (e.g. Kodak T-Max P3200, Ilford Delta 3200) and film rolls Cinestill 800T.

2. New 3D computed tomography machines (CT Scanners, such as Smiths Detection/Analogic):

• Appearance features: The entrance is mostly in the shape of a round drum, so there is no need to take out the laptop and liquids in the suitcase.
• Destructive power: The machine uses a high-energy X-ray tube that rotates 360 degrees to emit multi-angle cone-shaped high-intensity radiation to the luggage and calculate three-dimensional voxels. Even low-sensitivity film at ISO 100 will be permanently and fatally damaged after just one pass through a CT scanner.

2. Typical visual characteristics of film damaged by radiation

Damaged film develops physical damage that cannot be repaired through toning:

1. Sinusoidal Banding: There are wavy or diagonal intertwined gray fog bands with uneven density and soft edges across the film, which are completely consistent with the physical circle of the film wound in the cassette.
2. The dark parts are dead white (the fog value D-min soars): The originally transparent film base turns into a thick grayish green fog, causing the contrast in the dark parts to be completely lost during digital inversion or optical amplification, and the black turns into turbid and messy gray noise.
3. Severe color cast in color negative film: The three different silver halide emulsion layers of the color negative have different sensitivity rates to X-rays, resulting in the separation of the magenta and green channels, making the highlights appear red and the shadows appear green, making it impossible to pass color balance correction.

3. Actual measurement and usage limitations of lead foil protective bag (Lead Pouch)

1. Lead bag protection effectiveness: Lead bags (such as Domke Film Guard) can shield traditional low-dose X-rays.
2. Fatal Paradox under CT Machine:

• When security personnel see a completely opaque rectangular shadow of a pitch black lead bag on the CT screen, security procedures state that they must "see through the contents."
• The CT scanning system will automatically and intelligently increase the tube voltage and radiation dose for high-power local penetration focusing, or the security inspector will send the package back for repeated high-energy irradiation, which will intensify the radiation damage to the internal film.
• Conclusion: The lead bag is only suitable for traditional X-ray machines to prevent cumulative exposure; when encountering a CT scanner, it must be removed and applied for manual inspection.

4. Standardized practical procedures for applying for manual hand check (Hand Check) at global airports

1. Preparation before departure:

• Before traveling, remove all undeveloped films from their carton packaging and plastic tubes, and place them neatly into a completely transparent Ziploc Bag.
• Try not to load rolls in the camera body in advance; if there are rolls in the camera body, security inspection usually requires the camera to be passed through the camera, making it difficult to manually inspect the camera body alone.

2. Four-step communication skills at security checkpoints (bilingual in Chinese and English):

• Step 1 (take the initiative before entering the conveyor belt): Take the initiative to hold the transparent film bag in your hand, do not put it at the bottom of the luggage frame.
• Step 2 (polite statement to the security personnel):
• Chinese: "Hello, this is a high-sensitivity photographic undeveloped film. It is very sensitive to X-rays and CT scans. It will be completely scrapped when exposed to radiation. Can you please help with manual hand inspection (Hand Inspection)?"
• English: "Hello, I have unprocessed high-speed photographic film in this bag. It is extremely sensitive to X-rays and CT scanners. Could you please do a manual hand check for these?"
• Step 3 (cooperating with explosive trace detection ETD): The security inspector usually wipes both ends of the film cassette and the surface of the ziplock bag with test paper, and then puts it into an ion mobility chromatograph (ETD) to detect explosive residue, which takes about 30-60 seconds.
• Step 4 (strictly prohibited in checked luggage): Never put undeveloped film in checked luggage! The radiation intensity of airport check-in baggage security inspection machines is dozens of times that of carry-on security inspection machines. A single check-in will inevitably lead to the destruction of all films.

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