THE FOCAL LENGTH OF NEUTRON LENSES USING CAPILLARY OPTICS

Capillary-fiber optics have been shown to be a useful technique for gu iding and focusing both X-rays and neutrons by means of multiple refle ction in hollow glass tubes and the principles of X-ray and neutron le nses have been demonstrated. An optimum condition is derived for such a device. The focal length L of the focusing lens, the average critica l angle theta(c)BAR, of the material of the fibers and the radius R of the fibers that comprise the lens are related by the simple equation L = xR/theta(c)BAR, where the factor x depends on the particular optim ization required and the source of radiation used. The value of theta( c)BAR depends on the spectrum of the radiation transmitted by the lens .