Cathode rays, definition

Luminescence color is determined by visual comparison, by calculation of the color coordinates x and y from the emission spectrum, or by means of a tristimulus colorimeter under the excitation definitive for the application (UV radiation, cathode rays, etc.). 

Early work in this field was conducted prior to the availability of powerful radiation sources. In 1929, E. B. Newton "vulcanized" rubber sheets with cathode-rays (16). Several studies were carried out during and immediately after world war II in order to determine the damage caused by radiation to insulators and other plastic materials intended for use in radiation fields (17, 18, 19). M. Dole reported research carried out by Rose on the effect of reactor radiation on thin films of polyethylene irradiated either in air or under vacuum (20). However, worldwide interest in the radiation chemistry of polymers arose after Arthur Charlesby showed in 1952 that polyethylene was converted by irradiation into a non-soluble and non-melting cross-linked material (21). It should be emphasized, that in 1952, the only cross-linking process practiced in industry was the "vulcanization" of rubber. The fact that polyethylene, a paraffinic (and therefore by definition a chemically "inert") polymer could react under simple irradiation and become converted into a new material with improved properties looked like a "miracle" to many outsiders and even to experts in the art. More miracles were therefore expected from radiation sources which were hastily acquired by industry in the 1950 s. 

Apart from this extensive increase in power of the theoretical treatment, the fast cathode rays possess the practical advantage of easy manipulation, so that now, after but few years of development, certain methods of investigating structure by means of electron waves can be carried out with almost as great precision as has hitherto been possible in the analogous experiments with X-rays. In some respects, notably as regards times of exposure, some of the characteristic features of electron scattering give it a definite superiority. 

Many years ago, therefore, it became evident that Lavoisier s definition would have to be replaced by a new one more in harmony with the known facts of the case. Fortunately chdknists had not far to turn. In 1895 R ntgen, professor of physics in the University of Wtirzburg in Bavaria, discovered that when matter is bombarded with cathode rays it emits new rays of extraordinary penetrating power. These rays, often now called ROntgen rays, were termed X-rays as their nature was then unknown, just as iodine was referred to as substance X at the time of its discovery (p. 48) before it was recognised to be an element. 

Cathode-ray phosphors with such a long persistence are suitable to avoid or minimize flicker in the display. This is especially of importance when high-definition figures need to be displayed. For application in television tubes (moving pictures) or high-frequency oscilloscopes, such a long persistence is of course fatal. 

There were good reasons for preferring the latter alternative and assuming the cathode-ray particle to be much smaller than any atom. By 1911 this was proven definitely by the American physicist Robert Andrews Millikan (1868-1953), who succeeded in measuring, quite accurately, the minimum electric charge that could be carried by a particle. 

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