Radiant energy – Radiation controlling means
Patent
1996-02-26
1998-04-28
Anderson, Bruce
Radiant energy
Radiation controlling means
378149, G02B 5124
Patent
active
057448132
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present inventions relate in general to nuclear physics, more specifically to means for controlling beams of neutral and charged particles, and are aimed at bending such beams, their focusing, transforming a divergent radiation into a quasi-parallel one, and vice versa, its filtering and monochromatization.
BACKGROUND ART
Known in the art are a variety of methods and devices for controlling beams of neutral and charged particles, based use of interference and diffraction phenomena, e.g., Fresnel zone plates, Bragg crystals, multilayer mirrors (cf."Introduction to solid-state physics" by C. Kittel, Moscow, Gosudarstvennoe izdatelstvo fiziko-matematicheskoi literatury, 1963, p.73 (Russian translation).
However, use of such methods and devices fails to attain high radiation concentration and a large angle of beam bend.
These restrictions are eliminated in methods and devices that make use of multiple reflection.
In particular, there is known a method for controlling radiation beams using multiple reflection, realized in a system of curved hollow capillaries (cf. the paper "Wide-band X-ray optics with large angular aperture" by V. A. Arkadyev, A. I. Kolomiitsev, M. A. Kumakhov et al., "Advances in physical sciences", 1989, v.157, issue 3, pp.529-537 (in Russian).
A disadvantage inherent in said method and device resides in a considerable radiation attenuation due to inaccuracies in arrangement of the channels-capillaries during manufacture of the device, as well as a relatively narrow spectral band due to use of capillaries whose diameter exceeds an optimum size of channels. Trying to reduce said diameter in the construction under discussion faces considerable engineering difficulties.
In another heretofore-known device as per U.S. Pat. No. 5,192,869 published Mar. 9, 1993 and a method said device carries into effect, which are most similar to the herein-proposed inventions and wherein use is also made of the multiple reflection concept, the aforementioned disadvantages are partially overcome due to use of rigid support elements spaced definite distances apart from one another lengthwise the device and ensuring rigid fixing of the channel-forming elements at the places where they pass through the holes in the support elements. Appropriately selected arrangement of said holes provides correspondence of the axial lines of individual channels to the generating surfaces of a required shape. Used as channel-forming elements are glass capillaries or polycapillaries.
Such an optical system for controlling radiation beams resembles a barrel or a half-barrel in shape and is therefore given the name of a lens or a hemilens, respectively. Customs made up of capillaries are known as first-generation lenses (hemilenses), whereas those built up of polycapillaries, are known as second-generation lenses (hemilenses).
With the diameter of capillaries and polycapillaries on the order of 300 microns they lose their properties necessary for proper assembling, that is, they start "soaring" in the air as being hollow and cannot be given a required radius of curvature while being assembled, and the capillaries are liable to sag between the points of support. This restriction as to the diameter of capillaries and polycapillaries makes impossible radiation focusing into a spot having a diameter smaller than that of a capillary or the outside diameter of polycapillary. The smallest focal spot diameter attainable with the first- and second-generation lenses is 0.5 mm so that high radiation concentration is unattainable due to too a large focal spot diameter.
Finite size of channels imposes limitation on the range of energies used. With a preset focal length f, even though the radiation is a point-like one, a minimum angle of radiation incidence on the capillary peripheral zone is .theta.=d/2f, where d denotes the channel diameter.
It is desirable, for an efficient radiation transfer, that the parameter .theta. be close to or even less than the critical angle .theta..sub.c of reflection because with an increase in
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Charles Kittel, Introduction to Solid State Physics, New York:Wiley, 1956.
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