THE DISCOVERY OF X-RAYS - A SCIENTIFIC RE VOLUTION

W.C. Rontgen reported the discovery of X-rays in December 1895 after s even weeks of assiduous work during which he had studied the propertie s of this new type of radiation able to go through screens of notable thickness. He named them X-rays to underline the fact that their natur e was unknown. The news of this discovery immediately aroused an immen se interest in the public and also initiated intense research in sever al directions. Physicians and physicists begen as early as January 189 6 to use X-rays on patients to investigate the squeleton and subsequen tly the lung and other organs. This was the birth or radiology. Rapidl y they observed skin erythema, wich led to the idea of using X-rays ag ainst a variety of lesions. In June 1896 the first patient was treated by radiotherapy. J.J. Thomson (Cambridge, U.K.) showed that X-rays we re able to ionize gaz and the study of this phenomenon led to the disc overy of electrons in 1897. In order to understand the emission of X-r ays, H. Becquerel (Paris) investigated the role of the phosphorescence of the glass of the tube and while doing so discovered radioactivity in March 1896. X-rays and radioactivity were at the origin of the scie ntific revolution at the end of the 19(th) and the beginning of the 20 (th) centuries. Research on radioactive materials demonstrated the exi stence of atoms which had been till then only a convenient hypothesis for explaining chemical reactions, but whose reality was considered as dubious by most physicists. Moreover, interaction of particles emitte d by radionuclides and atoms enabled first the study of the structure of the atom and subsequently its nucleus. Matter, elements which were thought to be immutable were found to be transmutable, and eventually to disintegrate. The origin of the energy transferred to the radiation which was emitted appeared as a mystery and in order to explain it th e physicist had to accept that matter could convert into energy. In 19 03 Einstein established the equivalence between matter and energy. Mat ter, energy, electricity, light which were formerly considered as cont inuous quantities were found to be discrete : there are particles of m atter (elementary particles), energy (quanta, Planck 1905), electricit y (electron1), light (photons). Radioactive decay, particle interactio ns imposed a probabilistic physics which progressively replaced classi c deterministic physics. Radioactivity can be used as a clock to measu re time in the universe. Datations were made for fossils, art masterpi eces and also for the earth, the solar system and the universe. X-ray diffraction proved to be a powerful tool for studying cristals and mol ecules, in particular protein, and in 1953 enabled to demonstrate the DNA double helix. Hence X-rays and radioactivity originated a revoluti on in physics and science and in the vision of nature. The imperceptib le and yet so powerful rays demonstrated the deficiencies of our sense s. Mathematical entities and instrumentation must complement our sensa tions. The huge increment in our knowledge is accompanied by a divorce between the scientist and the layman who now often has great difficul ties understanding new concepts not only in physics but also in biolog y.