The discovery of x rays

While investigating the nature of cathode rays produced in a Crookes mbe that he had covered with a shield of black cardboard, ostensibly to prevent the cathode rays from escaping, Roentgen (Fig. 3.17) observed in 1895 the luminescent effect on a 

The Light Fantastic, p. 189, Penguin Books, Middlesex (1981). 

Partington, A Short History of Chemistry, 3rd ed., p. 357, Dover Publications, New York 

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Even the originator was hesitant to blow his own trumpet. In 1917, the elder Bragg published an essay on physical research and the way of its application , in a multiauthor book entitled Science and the Nation (Bragg 1917). Although he writes at some length on Rdntgen and the discovery of X-rays, he includes not a word on X-ray diffraction, five years after the discoveries by his son and himself. 

These detectors have been important in physics virtually since the discovery of x-rays, and they gained further importance with the advent of nuclear physics. They have not as yet become important in analytical chemistry, mainly because the electric currents they generate are so minute as to make ionization detectors less convenient to use for precise measurements than others. 

Crystallography is an advanced discipline [318], Modern crystallography has been developed since the discovery of X-ray diffraction in 1912 from the original basis laid down by classical crystallographers. One of the beauties of this modern discipline, while it can be somewhat mathematical, is the universal use of standardised notations and conventions, as developed through the International Union of Crystallography (IUCr). 

Chemical effects from the absorption of charged-particle irradiation were observed almost immediately following the discoveries of X-rays and the electron in the last decade of the nineteenth century. The field, though, remained unnamed until 1942, when Milton Burton christened it radiation chemistry. At present, it has developed into a vigorous discipline embracing radiation physics on one hand and radiation biology on the other. The purpose of this book is to give a coherent account of the development of this field with stress on the fundamental aspects. 

In the early years of Theosophy during Blavatsky s lifetime, the modem science that most occupied the movement was, without doubt, the theory of evolution rather than Victorian discoveries in physics and chemistry.4 While Blavatksy in Isis Unveiled and Secret Doctrine grappled in a limited way with modem physics and chemistry, she engaged much more fully with the work of alchemists, especially that of Paracelsus. Her defense of alchemical transmutation was based not upon contemporary science—though she asked of transmutation, Is the idea so absurd as to be totally unworthy of consideration in this age of chemical discovery (Isis 1 503)—but rather upon the exalted reputation of medieval and early modem scientists and alchemists who claimed to have witnessed transmutation (1 503-504). Moreover, the major events that launched modem particle physics—the discoveries of X-rays, the electron, radiation, radium, and radioactive decay—all occurred after Blavatsky died in 1891. 

Two fundamental discoveries about the structure of the atom and electromagnetic radiation also occurred during this period and provided a foundation for instrumentation that would be fundamental in furthering our understanding of soil chemistry. One was the discovery of X-rays, also sometimes called Rontgen rays, discovered in 1895, by W. Rontgen [24], The second was made by J. J. Thomson in 1912. He observed positive rays and described how these could be used to identify compounds and elements. Subsequently, he presented a clear description of the process in 1913. This led to the development of mass spectrometry [25],... 

It is clear that, along with the discovery of x-rays in 1895, Roentgen also found the chemical action of ionizing radiation. He drew attention to the similarity of the photographic effect induced by light and x-rays. Application to medicine appeared very quickly, followed by industrial applications. However, this field of investigation remained nameless until Milton Burton, in 1942, christened it radiation chemistry to separate it from radiochemistry which is the study of radioactive nuclei. Historical and classical work in radiation chemistry has been reviewed by Mozumder elsewhere [1]. Here we will only make a few brief remarks. 

Max von Laue, 1879 - 1960. German professor for physics. Nobel prize for physics 1914 for the discovery of X-ray diffraction in crystals. 

Symmetry is the fundamental basis for descriptions and classification of crystal structures. The use of symmetry made it possible for early investigators to derive the classification of crystals in the seven systems, 14 Bravais lattices, 32 crystal classes, and the 230 space groups before the discovery of X-ray crystallography. Here we examine symmetry elements needed for the point groups used for discrete molecules or objects. Then we examine additional operations needed for space groups used for crystal structures. 

The discovery of x-rays provided crystallographers a powerful tool for the thorough determination of crystal structures and unit cell sizes [20-26], X-rays have wavelengths between 0.2 and 10 nm. As x-rays possess dimensions comparable to the interplanar distances in crystals, x-ray crystallography is an ideal nondestructive method for material characterization, since nanometer parameters as well as macroscopic properties of the tested samples can be determined from x-ray diffraction data. 

A ciystal may for some purposes be described in terms of a set of three crystal axes a, b, and c, which may or may not be of equal length and/or at right angles, depending on the syimnetiy of the crystal. These axes form the basis for a coordinate system with which the crystal may be described. An important property of crystals, known at least a centrrry before the discovery of X rays, is that the crystal axes for any crystal can be so chosen that all crystal faces can be described by eqrratiorrs of the form... 

The purpose of this article is to review the development of radiation chemistry which began with the discovery of x-rays by Roentgen(l) in 1895 and shortly afterwards of radioactivity by Becquerel(2), which in both cases Involved the observation of chemical change in photographic plates and luminescence in certain phosphors. Clearly, in the space available, the review will be restricted and subjective, but will, it is hoped, give the general framework in which the subject has developed. 

Shortly after the discovery of X-ray diffraction by von Laue and von Knipping in 1910, Debye and Scherrer (1916) in Germany and HulP (1917) in the United States independently pioneered X-ray powder diffraction. Zachariasen " (1949) determined the first structures solely from powder diffraction data by using an intuition-based trial-and-error approach. The structures of UCI3 as well as a- and /S-UFs were solved this way. More than a decade later Zachari-asen and Ellinger (1963) used direct method procedures to... 

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