Many people wonder if wrapping items in aluminum foil can conceal them in an xray. This is a common question, as xrays are frequently used for security screening at airports, government buildings, and other facilities. The principle behind xrays allows them to see through certain materials, but not all. Understanding how xrays work and the properties of aluminum foil can shed light on whether foil can effectively hide items from x-ray detection.
How do x-rays work?
X-rays are a type of electromagnetic radiation, like light waves or radio waves. However, x-rays have much shorter wavelengths and higher frequencies than other types of electromagnetic waves. When x-rays hit matter, some of the waves get absorbed, while others pass through. This allows x-rays to penetrate many materials to create images of what’s inside.
The key to x-ray imaging is that different materials absorb x-rays at different rates. Dense materials like metal absorb a lot of x-rays, so they show up as lighter on the final image. Materials like air allow most x-rays to pass through, so air will look dark on an x-ray. The contrast between dense and less dense zones is what creates detailed x-ray images.
X-ray absorption
The level of x-ray absorption depends on a material’s density and atomic composition. Denser materials absorb more x-rays because they contain more molecules per unit volume to interact with the radiation. Materials made of elements with higher atomic numbers also absorb more strongly, because atoms with larger nuclei present a bigger target.
Lead is very effective at absorbing x-rays due to its high density and high atomic number. That’s why lead aprons and shields are used to limit x-ray exposure. Air has low density and low atomic numbers, so it allows most x-rays to pass through unimpeded. Materials like plastic and ceramic fall somewhere in between. They absorb x-rays to a moderate degree and show up as various shades of gray on x-ray images.
Properties of aluminum foil
Aluminum foil is thin sheet metal made from aluminum. It has a density of about 2.7 g/cm3, which is much lower than high density metals like lead and iron. But aluminum still has a higher density than most plastics, meaning it will absorb x-rays more than many common materials.
Aluminum also has a moderately high atomic number (13) compared to lighter elements. While not as x-ray opaque as lead, aluminum still absorbs a fair portion of x-ray radiation. This is why aluminum plates are sometimes used as protective barriers for x-ray machines.
The thickness of the aluminum foil also plays a role. Standard household foil is quite thin, on the order of 0.2 mm. Thicker specialty aluminum sheets would absorb even more x-rays. But in general, household foil is not extremely dense or thick relative to many other metals.
Does foil block x-rays?
Aluminum foil does partially block x-rays, but it does not block them entirely. The exact amount of x-ray absorption depends on the energy (frequency) of the x-ray beam as well as the thickness of the foil.
Higher frequency x-rays, like those used for medical/dental imaging, are mostly absorbed by aluminum foil. However, the lower energy x-rays used in airport security screening can partially penetrate through foil.
One study exposed sheets of household aluminum foil to low-energy x-ray beams and measured how much radiation passed through. For standard kitchen foil about 0.2 mm thick, about half of the incident x-rays were able to pass through the foil. For reference, plastic packaging absorbed only 10% of these x-rays while lead sheeting absorbed over 99%.
So a single sheet of aluminum foil blocks about half of lower frequency security x-rays. Multiple sheets would absorb more of the radiation, but some x-rays would still get through. The foil may obscure the shapes of items wrapped inside, however airport x-ray machines also use sophisticated imaging software to identify concealed items.
Why foil doesn’t block all x-rays
There are a few reasons why aluminum foil doesn’t completely block security x-rays:
- Low density – While aluminum has a decent density, it is still much less dense than lead which is very x-ray opaque.
- Moderate thickness – Standard kitchen foil is less than a millimeter thick. More layers would absorb more x-rays, but a single sheet is quite thin.
- Low x-ray energy – Airport scanners use lower frequency x-rays that can partially penetrate metals compared to medical x-rays.
All these factors combined allow some of the x-ray waves to pass through foil. Although the foil may obscure shapes to some degree, it does not conceal items completely.
Does hiding items in foil fool airport x-ray machines?
It is very difficult to fool airport x-ray machines by hiding contraband in aluminum foil. While foil does absorb some x-rays, modern security scanners have advanced imaging capabilities and can still detect concealed items.
There are a few reasons foil is ineffective at hiding prohibited items:
Sophisticated imaging software
Airport x-ray machines don’t just take single static pictures. They use multi-view imaging with automated threat detection programs that can digitally reconstruct 3D images of bags and highlight anomalies. This sophisticated software can identify disguised items based on subtle shadows and discrepancies in the images.
Dual x-ray energies
Some advanced scanners use two different x-ray energies simultaneously. Low energy x-rays image soft materials well while high energy x-rays better penetrate metals and foil. Combining the two images allows computers to find concealed items that neither beam would detect on its own.
Advanced algorithms
Security scanning computers use complex algorithms to automatically analyze images and determine potential threats. Even if a human eye can’t discern a hidden item in the x-ray, computer analysis of the data may pick up clues like variations in density and shape to flag suspicious items.
Operator inspection
Even with automated detection, x-ray operators also visually inspect the scans on their monitors and can spot irregularities or foil-wrapped items. They may flag suspicious bags for manual searches if the x-ray images look obscured.
Examples where foil failed to conceal items
There are many real world examples where people attempted to hide prohibited items in aluminum foil but were caught by airport x-ray screening:
Guns and ammunition
Guns wrapped in foil show up distinctly on x-rays due to their recognizable shape and density. Bullets and shells are also easy to detect. Foil disguises may obscure the outlines but the distinctive metal items shine through.
Explosives
Items like dynamite sticks have been hidden in foil lined luggage only to be thwarted by eagle-eyed operators or automated detection programs. Explosives can be identified even in foil due to their unique density signatures.
Drugs
Smugglers have tried concealing illegal drugs by wrapping them in aluminum foil. But illegal narcotics and paraphernalia can still be recognized on scans based on their morphology and material properties.
Currency
Wads of paper money wrapped in foil are sometimes spotted if the blocky outlines or sheet edges give them away under x-ray. Large amounts of undeclared cash trigger scrutiny as well.
Jewelry/precious metals
High density metals like gold and silver jewelry are obvious on x-rays even through foil shielding due to their brightness and shape. Coins and bullion can also be spotted.
Better ways to beat airport x-rays
Rather than relying on aluminum foil, there are better ways to reliably beat airport x-rays:
Organic materials
Radiographically “quiet” materials that resemble organic tissues on scans can better disguise items against automated threat detection programs. Liquids like water also absorb x-rays comparably to the human body.
Careful concealment
Shaping prohibited items to mimic everyday objects that routinely pass screening can outwit x-ray operators. Disguising contraband to look like food or electronics in scans fools humans more easily than foil.
Teeny tiny amounts
Large weapons and items are obvious, but minuscule components evade even sophisticated detectors. Microdots of narcotics on paper, tiny detonators, embedded electronics, and microscopic toxins slip past.
Body cavities
X-rays and scans can’t penetrate into the body itself (without highly invasive searches). So swallowed balloons of drugs or small items hidden in body orifices avoid detection, but pose serious health risks.
Conclusion
In summary, aluminum foil does block some x-rays due to its density and thickness. But household foil does not completely stop airport security x-rays which can still penetrate foil and identify hidden contraband. Sophisticated imaging software and dual energy x-rays allow modern scanners to find concealed items even with foil shielding. While foil may obscure shapes to the naked eye, automated threat detection programs are not so easily fooled. Clever concealment designs or body cavity hiding can defeat security x-rays more reliably than aluminum foil. So next time you’re trying to sneak your sandwich through a TSA checkpoint, leave the foil at home!