Saturday, January 26, 2013
PARIS - Scotch tape is not only see-through, it can also see through, for the product can be used to take X-rays, bemused scientists say.
Peeling tape from a roll of Scotch releases tiny bursts of X-rays that are powerful enough to take images of bones in fingers and hands, researchers have found.
The unusual discovery was made by a University of California at Los Angeles team, intrigued after hearing that Soviet scientists in the 1950s found that sticky tape, when separated at the right speed, released pulses in the X-ray part of the energy spectrum.
Reporting in Thursday's issue of the British-based science journal Nature, the investigators used a motorised peeling machine to unwind a standard roll (25.4 metres in length by 19 mm) of Photo Safe 3M Scotch tape at a speed of three centimetres (1.18 inches) a second.
By placing the machine in a vacuum, they were able to measure X-rays that were enough to take images.
"We didn't believe it. We really didn't think it could be true," co-author Carlos Camara told AFP in a phone interview, referring to the team's initial scepticism.
"We took some pictures of our hands to see the bones and prove that it was possible. We have a whole collection (of pictures)... it is absolutely remarkable."
As to precisely why this phenomenon occurs, Camara admits: "That is a mystery."
The core theory is something called "triboluminescence," which occurs when two contacting surfaces move relative to each other.
As the tape peels, the sticky acrylic adhesive, on the back of the tape, becomes positively charged, while the polyethylene roll becomes negatively charged, according to this hypothesis.
At a reduced atmospheric pressure, the mechanical act of pulling apart the two surfaces causes electric fields to build up that then trigger discharges of energy.
This accelerates electrons on the adhesive to very high speeds and when they whack into the positively-charged tape roll, X-rays result. The pulses last for a billionth of a second, with an intensity of 100 milliwatts.
"It is a discharge process," said Camara. "It is not clear exactly what mechanism is taking place, but electrons are plainly flying from one side to the other at very high speed and when they hit the other side and they stop, X-rays are emitted.
He added that there could one day be a useful outlet to the discovery -- X-ray machines that would be cheaper and safer than conventional machines that require a permanent radioactive source and a highly trained technician for maintenance.
Posted by Jeremy Conrad at 9:40 AM