Juan Escobar
Juan V. Escobar

UC MEXUS-CONACYT Doctoral Fellow Juan Escobar joined the UCLA Department of Physics and Astronomy to study the science of interacting surfaces, specifically exploring the mechanisms that release radiant energy-light produced by the breaking of asymmetrical bonds in a crystal when the material is scratched, crushed, or rubbed.

An article by Escobar, his adviser, and lab colleagues, published in the October issue of Nature, has attracted a great deal of attention from scientists all over the world. The article, “Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape,” 1 explains that ordinary, commercial adhesive tape, unwound in a vacuum, can generate strong enough X-rays to reproduce clear images of the bones in the fingers. While the underlying science is highly sophisticated for anyone but fellow scientists, the concept was easy to translate into everyday language. Escobar, his adviser Seth Putterman, and two postdoctoral researchers suddenly found themselves in demand among print and electronic media reporters from all over the world.

escobar_finger_ X_ray

According to Escobar, the basic science involved in the production of X-rays under these conditions is not new. More than 60 years ago, Russian scientist J. W. Obreimoff found evidence that the mica group of minerals could emit X-rays when split in a vacuum. Obreimoff's colleagues performed other sets of experiments in 1953 and in 1989 showing that adhesives also would emit X-rays when peeled in vacuum.

When a former postdoctoral researcher working in Putterman's lab found that mercury emits light as it slides in glass, Escobar and his colleagues dug into the literature for other such phenomena and discovered Obreimoff's work. In response, they repeated the experiment and found that peeling tape, at a pace of about three centimeters per second, not only emitted sporadic X-rays, but was sufficient to create an image. They were astounded by the X-ray's intensity and duration. As Putterman told the Associated Press, "We're marveling at Mother Nature."

Escobar and his colleagues have measured the energy using an X-ray detector and confirmed that the energy and the length of the flashes go beyond anything previously recorded. According to Escobar, this technology could easily be adapted as a cheaper, portable X-ray machine for use outside of medical facilities, and in developing countries where electricity is expensive. The phenomenon could provide the foundation for simple medical devices using bursts of radiation to destroy tumors. There is also a possibility of detecting such X-ray emissions from composite materials in airplanes and automobiles as they fatigue, which usually give no hint of wear before breaking.

For the moment, Escobar is focusing on his dissertation, "The role of electrostatics in friction and adhesion," which deals with the very issues exposed by the adhesive tape experiments. Following completion of his degree, he hopes to get back to exploring the implications of these initial discoveries. He and his colleagues in Putterman's lab will try to build an X-ray generator that brings two pieces of tape together and separates them at accelerated rates with a piezoelectric device, which would result in a new, controllable source of radiation that they might be able to miniaturize. In the meantime, UCLA has taken steps to protect the device that may hold the key to many possible future developments, and has filed patent applications on the device.

A video demonstrating the process is available on YouTube http://www.youtube.com/watch?v=r63e5y3Z3R8.

Juan Escobar can be reached at 310-592-9434 or escobar@physics.ucla.edu

1 “Correlation between nanosecond X-ray flashes and stick–slip friction in peeling tape,” Nature, 23 October, 2008, by Carlos G. Camara, Juan V. Escobar, Jonathan R. Hird & Seth J. Putterman