EMISSION AND TRANSMISSION OF RONTGEN 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 relation 

 between 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 see 

 at once how very different the transmission curves are from those where an aluminium 



I6O 



140 



THICKNESS , 



0025 CM. 

 'CU SCREEN - 



0075 



0125 



Fig. 4. Copper screen, 28,000 volts. 



screen was used. As the thickness of screen is increased, silver and lead rise into 

 place 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 nickel 

 are used, more radiation emerges from a copper screen than is the case when the 

 anticathode is of platinum or lead, although the latter have much higher atomic weights. 



8 2 



