Precision bending

A new method to bend beams of X-rays could make diagnosis precise

Published: Sunday 30 November 1997

x-ray is an important diagnostic tool in medical science But researchers have been facing the problem of focusing these beams since ordinary lenses do not bend them. Now, J Golovchenko and C Liu at the Harvard University, usa , have used a curved wall of polished silicon to bend the beams of high energy x -rays by nearly 13 ( Science , Vol 277, No 5328).

Researchers have been using reflection from crystals for bending x -rays before. The idea is to make the x -ray fall at grazing incidence on the surface from where the beam bounces off like a stone on the surface of water. But this technique is inadequate for large deflections. The principle applied by Liu and Golovchenko is the one, which is used in whispering galleries. Sound waves travel around a circular gallery by repeated reflections from curving walls.

One year back, scientists in Russia had demonstrated the use of this principle for low energy x -rays. But Liu and Golovchenko have been able to demonstrate its use for high energy beams also. Using a 18 mm long polished silicon wafer they bent it into an arc. When a beam of high energy x -rays was made to fall on it at a shallow angle, the x -rays just brushed against the surface and hit it again further down the arc. With nearly 100 reflections, the researchers were able to deflect the beam about 13 degrees from its incident path.

The deflection of high energy x -rays by using the whispering gallery principle provides a proof that in principle it is possible to develop lenses for use with such x -rays. These lenses could be important components of x -ray lasers, which are already being used and would become more popular in future. Though it is only a novel idea at present, which works in the laboratory.

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