Dr HH Mate
X-rays or Roentgen X-rays, are electromagnetic waves in which periodically variable electric and magnetic fields are perpendicular to each other and to the direction of propagation. Thus they are identical in nature with visible light and all the other types of radiation that constitute the electromagnetic spectrum such as ultraviolet, infrared, gamma rays form radioactive atomic disintegrations, microwaves, and radio or hertzian waves. In general, X-rays are generated as the result of energy transistors of atomic electrons caused by the bombardment of a material of high atomic weight by high energy electrons.
Roentgen’s findings: The unequivocal establishment of the nature of these rays was not made in W.C. Roentgen’s experiments following the discovery of a new kind of ray” in 1985. In his first communication, Roentgen described the properties of these rays as follows : They were invisible; and moved in straight lines, were unaffected by electric or magnetic fields, and hence not electrically charged; passed through matter opaque to ordinary light since they penetrated through the black cardboard around his cathode ray tube; were differentially absorbed by matter of different densities or of different atomic weights; affected photographic plated; produced fluorescence in certain chemicals, such as in the barium platinocyanide screen with which the initial discovery was made and in the wall of his glass tube opposite the cathode; produced ionization in gases; and were evidently produced by the stoppage at the anode of the beam of rays, as identified by J.J. Thomson in 1877 as electrons, issuing from the cathode in his vacuum tube.
Along with all these definitive characteristics of the X-rays, however, other crucial experiments designed to establish similarity or differences from ordinary light were clearly called for. The fundamental optical properties of light were well established in 1895; reflection from mirrors, refraction in prisms (i.e, change in direction in passing from air into glass, for example), by means of which a beam of white light could be spread out into a rainbow or spectrum of colours; diffraction by narrow slits or ruled gratings, also a method of producing spectra; and polarization, or constraint of the transverse vibrations to a single direction. In spite of the best efforts of Roentgen, no indubitable evidence of any of these four optical phenomena could be found. Hence the designation “ X “- unknown was assigned by W.C. Roentgen. Many theories were proposed to account for the apparently unique quality of x-rays, which seemed to be so closely similar and yet so greatly different from light; some suggested that they were vortex rings in the ether, and waves with longitudinal vibrations, that is, vibrations parallel to the direction of propagation as in small waves, instead of transverse as with light.
Later discoveries: Inevitably, other scientists studying the enigma found the essential experimental conditions to prove that X-rays can be polarized, refracted in prisms and in crystals; reflected by mirrors, and diffracted by ruled gratings. Instead of being refracted in passing from a less dense medium (air) to a more same direction as light so that the index of refraction is always greater than 1, X-rays are deviated in the opposite direction by a very small amount, so that the index of refraction is less than 1 by an amount as small as 10-6. Thus total reflection from mirror is observed only when the beam impinges at a very small grazing angle, a necessary condition understandably missed by W.C. Roentgen. Similarly, the beam must graze a ruled diffraction grating if a spectrum is to be observed. To be continued
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