Peeling a roll of ordinary sticky tape can generate 100 milliwatt pulses of X-rays, enough to capture a human finger on X-ray film, according to a new study by UCLA scientists. They claim to have found the cheapest way to produce X-rays of that scale.
"At some point we were a little bit scared," says Juan Escobar, a member of the research team. But he and his co-workers soon realized that the X-rays were only emitted when the kit was used in a vacuum [Nature News].
Their kit consisted of a vacuum-enclosed machine, reminiscent of a video casette player, that peeled a roll of Photo Safe 3M Scotch tape at a rate of 3 cm per second.
Rapid pulses of X-rays, each about a billionth of a second long, emerged from very close to where the tape was coming off the roll. That's where electrons jumped from the roll to the sticky underside of the tape that was being pulled away, a journey of about two-thousandths of an inch, Escobar said. When those electrons struck the sticky side they slowed down, and that slowing made them emit X-rays [AP]. This type of energy release is known as triboluminescence
— the same principle behind the fun trick of crunching on Wint-O-Green Live Savers to produce blue sparks.Although the idea of peeling tape to emit X-rays was first suggested by Russian scientists in the 1950s, the new study, which made the cover of Nature [subscription required], comes as a shock to many in the field.
"You wouldn't have thought that so much of the mechanical energy would come out as X-rays," says Ken Suslick, an expert in mechanoluminescence.... "The adhesive on the tape is an amorphous liquid, not crystalline. What's causing the transfer of charge, of electrons or protons, what the accepting and donor groups are — these things are much less clear" [Nature News].
The researchers themselves are not exactly clear on the details of the phenomenon, but they say they are confident there is room for improvement; other types of tape may increase the X-ray yield by magnitudes of tens or hundreds. They are already filing a patent for their device, which could be developed into inexpensive hand-operated X-ray machines. Co-author Carlos Camara sums it up: "Just peeling tape is the quickest, cheapest way to provide X-rays... It's X-rays for everyone"
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