The Emission and Transmission of Rontgen Rays . ardsshow weak maxima at a thickness of about 0*07 cm. of screen. Thus for the range003 to 0*07 cm. the rays from these metals are more penetrating to aluminium thanare the rays from platinum, and we thus have a region over which selectivetransmission is manifested. It will be noticed that for screens thicker than about 2 mms. an alteration in thethickness produces very little change in the relative amounts of radiation from the X «/ CD EMISSION AND TRANSMISSION OF RQNTGEN RAYS. 131 different metals. The inference is that all the beams are now sim
The Emission and Transmission of Rontgen Rays . ardsshow weak maxima at a thickness of about 0*07 cm. of screen. Thus for the range003 to 0*07 cm. the rays from these metals are more penetrating to aluminium thanare the rays from platinum, and we thus have a region over which selectivetransmission is manifested. It will be noticed that for screens thicker than about 2 mms. an alteration in thethickness produces very little change in the relative amounts of radiation from the X «/ CD EMISSION AND TRANSMISSION OF RQNTGEN RAYS. 131 different metals. The inference is that all the beams are now similar in composition,and we should therefore be justified in expecting, at this stage, some evident relationbetween intensity and the atomic weight of the radiator. The point is gone into later(p. 135), but it may be stated at once that the two are roughly proportional. Copper Screens.—If we now consider the case of the copper screens (fig. 4), we seeat once how very different the transmission curves are from those where an aluminium I60r™. 0025 cm,THICKNESS or CU. SCREEN *Ol25 0150 Fig. 4. Copper screen, 28,000 volts. screen was used. As the thickness of screen is increased, silver and lead rise intoplace as before, but iron, nickel, and copper now increase their values and form well-marked maxima. Over a considerable range, when anticathodes of copper and nickelare used, more radiation emerges from a copper screen than is the case when theanticathode is of platinum or lead, although the latter have much higher atomic weights. s 2 132 ME. C. KAYE ON THE It will be noticed that the nearer the atomic weight of the radiator is to that ofcopper, the more marked and extensive is the maximum. The higher the atomic weight, the thicker is the screen at which the peak of thecurve occurs. The diagram provides a good indication of the amount of radiationspecially penetrating to copper which is present in each case. The resemblancebetween the radiations from nickel and copper, es
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