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Two physicists, one of them American and one Soviet, have developed
a revolutionary technology for focusing X-rays which could have spectacular
applications in medicine, computer chip manufacture, materials analysis
and astronomy.

The new ‘lens’ is actually a bundle of up to several million hollow
glass capillary tubes that guide the X-rays and focus them to a converging
beam or parallel beams. The technique is the result of 20 years of collaboration
between Walter Gibson of the State University of New York at Albany, and
Muradin Kumakhov of the Kurchatov Institute of Atomic Energy in Moscow.
The two have formed a partnership to continue research and have also created
a company to commercialise the lens.

X-rays, like visible light, scatter as they leave their source, and
lose intensity as they get farther away from the source. Å®ÉúСÊÓƵs have
long known, says Gibson, that X-rays can be reflected off solid, smooth
surfaces if they strike them at a very low angle. An X-ray can thus be guided
down a hollow glass tube. But Kumakhov, Gibson says, was the first to suggest
shrinking the size of the capillaries – from 0.2 millimetres to 70 nanometres
– and bundling them together to produce beams.

The ‘Kumakhov lens’, as Gibson has dubbed the device, can focus extremely
high densities of X-rays onto small spots. Gibson predicts that this will
make it possible for radiologists to direct radiation precisely onto tumours,
while avoiding healthy tissue. The new lenses have already ‘achieved spot
sizes as small as 30 micrometres, with X-ray intensities in the spot up
to 10 000 times as high as can be obtained without the lens’, Gibson says.

Tightly focused beams of X-rays may also change the chip-making business.
All present-day chips are made using optical lithography, in which visible
light is beamed onto silicon through holes in masks. Since X-rays have a
much shorter wavelength than light, they are theoretically capable of creating
much smaller features on chips. X-ray lithography could pack many more circuits
on each silicon wafer, meaning smaller, more powerful chips. Up until now,
however, dispersion has made it impossible to get enough X-rays to the chip
without using a synchrotron. Synchrotrons produce intense beams, but cost
as much as $50 million each. The new lenses ought to make X-ray lithography
possible with conventional sources, Gibson says.

John Warlaumont, manager of X-ray and ion beam research at IBM’s research
laboratory in New York says that although conventional optics will probably
suffice for the 64-megabit memory chips now under development, ‘it is not
certain that optical lithography will be able to do it for the 256-megabit
generation of chips.’ IBM is ‘interested in this work’, he says.

The Kumakhov lens could also be applied to X-ray astronomy. ‘All the
X-rays coming from space are parallel,’ says Gibson. ‘If we turn this kind
of lens upside down, a parallel X-ray beam can enter the large end of the
lens and be focused to a small spot.’ Concentrating these X-rays, he believes,
will make it possible to make lighter and cheaper instruments for astronomers.

The lens can focus neutrons as well as X-rays. ‘Up until now, there
has been no way to focus thermal neutrons. This could be important to materials
analysis. It should permit three-dimensional analysis, rather than just
surface studies using X-rays and neutrons,’ says Gibson.

Gibson plans to continue his research at the newly founded Center for
X-ray Optics at the university, while Kumakhov will work at a similar Institute
for Roentgen Optical Systems in Moscow. Gibson’s son David has founded a
company, X-Ray Optical Systems, to pursue commercial applications.