Thursday, October 23, 2008
Powerful x-rays made from sticky tape
Peeling ordinary sticky tape can generate bursts of X-rays intense enough to produce an image of the bones in your fingers.
Seth Putterman and colleagues from the University of California, Los Angeles used a motor to unwind a roll of sticky tape and recorded the electromagnetic emissions. Ripping the tape from its roll at 3 centimetres per second generated X-ray bursts of 15 kiloelectronvolts – each lasting one-billionth of a second, and containing over a million photons.
Putterman admits he is not sure exactly what is going on. "My attitude is to marvel at the phenomenon – all we are doing is peeling tape, and nature sets up a process that gives you nanosecond X-ray bursts."
Exactly what drives this process is still a mystery, but it is well known that if two surfaces rub over one another, one becomes positively charged and one negatively charged.
In this case, the sticky adhesive becomes positive, and the polyethylene roll negative. This charge difference builds up until an electron jumps from the adhesive to the roll, with enough energy to produce X-rays when it hits the tape.
The strength of the X-rays means that they could be a useful source for X-ray photography.
Sticky tape fusion
Putterman has even loftier ambitions. "The energy in the X-rays is enough to generate nuclear fusion, if it is given to the molecules rather than the electrons," he says. "It's a matter of engineering design, not physics."
Tom Todd, chief engineer of UKAEA Culham Division says, "It is true that the emitted X-ray energies are broadly representative of the electron energies – and that, if you could produce copious quantities of deuterium and tritium [the heavy hydrogen atoms needed for fusion] ions at around 15 keV, in sufficiently high density, they would produce fusion reactions."
However, it is unlikely that all these conditions will be met at the same time, so any power produced from the fused nuclei would be tiny, compared to the power required to unwind the sticky tape.
"It's not unphysical, just uneconomical by a great many orders of magnitude," concludes Todd.
Journal reference: Nature, DOI: 10.1038/nature07378