Secondary 7 Radiation. 

 Absorption of the Primary Radiation, 



233 



In these experiments four radiators were employed con- 

 sisting of carbon, aluminium, zinc, lead, each of weight about 

 470 grs. The ionization currents were measured in the 

 electroscope when the radium emanation was screened with 

 lead *084 cm. thick and when it was screened with lead 

 ( k 084+ri4 cm.) thick. Allowing of course for the effect 

 without the radiator in position, the absorption coefficient of 

 the direct radiation was thus indirectly determined. 



Table III. contains the results for the four positions (fig. 2) 

 when the side of the electroscope was *202 cm. aluminium. 



Table III. 



Radiator. 



Absorption coefficients measured in 1*14 cm. lead. 



E x - 



E 2 . 



E 3 - 



E 4 . 



2 - 26 cm. carbon ... 

 1"3 cm. aluminium . 

 0'5 cm. zinc 



■88 

 •84 

 •85 

 •70 



•90 

 •90 



•85 

 •67 



•90 

 •90 



•85 



•87 



•88 

 •88 

 •88 

 •88 



0"326 cm. lead 



From Table III. it is seen that when carbon, aluminium, 

 and zinc are used as radiators, the distribution of the secon- 

 dary radiation is independent of the "hardness" of the 

 primary 7 rays ; but this is not the case with lead as radiator, 

 for now the lead absorbs the softer 7 rays from radium B, 

 which in the case of the other radiators would probably 

 have appeared on the emergent side. Experimenters have 

 generally found with X rays that the scattered rays are of 

 the same penetrating power as the primary rays, so that a 

 screen placed in the primary beam will absorb these rays in 

 the same proportion as it would absorb the scattered radiation 

 when placed in front of the electroscope. This is by no 

 means true with the 7 rays and the secondary 7 rays. It 

 would therefore appear that the secondary 7 rays must be 

 the outcome of a transformation in the primaiy beam. This 

 question will be discussed later in the paper. 



In Table IV. are given the corresponding results when the 

 side of the electroscope was '084 cm. lead. 



