In an unexpected finding that could have applications in medicine and elsewhere, UCLA researchers have found that unspooling a simple roll of Scotch tape produces X-rays -- enough to produce clear images of their fingers.
The discovery could eventually lead to, among other things, compact X-ray sources that could be used for treating cancer, according to a study published Thursday in the journal Nature.
Although the researchers suspected that the process might produce X-rays, they were astounded by their intensity and duration, said Seth Putterman, a UCLA physicist and lead author of the study. "We're marveling at Mother Nature."
The phenomenon is known as triboluminescence and is similar to what causes sparks of light to be emitted when one bites on wintergreen-flavored LifeSavers in the dark. The process is not entirely understood but may involve, in part, a separation of charges during the rubbing of two materials together or the separation of the tape.
When the charges reunite, light -- and X-rays -- can be produced, just like in a lightning strike.
To study the phenomenon, Putterman's students Carlos G. Camara, Juan V. Escobar and Jonathan R. Hird constructed a device that would unspool the tape at a steady rate of about 1.3 inches per second.
When they placed it in a vacuum and turned it on, they measured emitted light and X-rays.
What was surprising was that the X-rays were not produced continuously, but were emitted in nanosecond bursts containing about 1 million X-ray photons apiece, the equivalent of about a tenth of a milliwatt of energy. That was enough energy to produce an X-ray image in a second, compared with about a third of a second required for a dental X-ray, Putterman said.
"We're getting flashes," he said. "How do you concentrate the energy? How does it come out as flashes? The mathematical equations are going to be very interesting."
The team's next effort will be to try to build an X-ray generator that brings two pieces of tape together and separates them at, say, 1,000 times per second with a piezoelectric device. "We would have a new, controllable source of radiation, and have to look at the possibility it could be miniaturized," he said.
Putterman also envisions nuclear fusion. If the constituents of the adhesive were deuterated -- hydrogen atoms replaced with deuterium -- it might yield fusion neutrons, although there would be no net energy increase.
He noted that there is no danger in using Scotch tape. Without a vacuum, air molecules intercept the X-rays, rendering them harmless.