120 Dr. Russell and Mr. Chad wick on the <y Rays of 



Excitation of y- rays by the a-rays in Copper and 

 in other metals. 



The main quantity of polonium was transferred from 

 aluminium to copper by dissolving the aluminium in HC1, 

 evaporating the solution to dryness, dissolving the aluminium 

 chloride in water, and rotating a clean copper plate varnished 

 on one side in the solution for an hour. The 7-radiation 

 from this plate was then analysed in the usual way. 



Both in penetrating power and in intensity, the radiation 

 from polonium on copper was different from what it had 

 been when the polonium was deposited on aluminium. The 

 intensity measured under the same experimental conditions 

 was, for equal quantities of polonium, about three times 

 greater on copper than on aluminium. This amount varied, 

 however, according as the copper oxide and chloride on the 

 surface of the copper was quite dry or not. Two types of 

 radiation were found to be present. One was the same in 

 intensity and penetrating power as that emitted from 



aluminium, with a value of ^.=215, the other giving a 

 value ~ = 1300 about. This new radiation must be due to 



excitation in the copper by the a-rays. It is possibly the 

 characteristic radiation of copper in series L. 



The active material was next transferred back to aluminium 

 by volatilization, and the intensity measured again. No 



other radiation except that having a value of p. =215 could 



be detected, and the copper was inactive. Part of the main 

 quantity of polonium was then deposited on platinum foil 

 and the radiation investigated. No evidence of an excited 

 radiation was obtained. The rest of the polonium was vola- 

 tilized on to lead foil. The amount and absorbability of the 

 radiation in this case were approximately the same as when 

 the polonium was deposited on aluminium, except that the 

 absorption produced by the first thickness of aluminium w^as 

 rather greater than before. The difference, however, was 

 0*2 div. per minute only, and therefore too small to be 

 regarded as definite. 



It is thus seen that when polonium is deposited on metals 

 of high atomic weight like platinum and lead, the excited 

 radiation, if produced at all, is small compared with that 

 excited in an element of low atomic weight similar to 

 copper. 



