364: Taylor — Retardation of Alpha Bays by Metals. 



obtained is nearly constant for all the sheets of the metal. 

 This is shown in column 4, Table Y. Thus for sheets of the 

 same metal the rate at which the air-equivalent of each sheet 

 changes with a change in the range of the entering a-particles, 

 is proportional to its air-equivalent when nearest the radium. 

 The approximately constant numbers in column 6, Table Y 

 show that the percentage rate of change in the air-equivalent 

 for any metal is nearly proportional to the square root of the 

 atomic weight. The agreement of the values in columns 4 

 and 6, Table Y is as good as could be expected since the slopes 

 of the curves in figure 1 could only be determined roughly. 

 The proportionality is indeed only approximate, since the 

 curve for any one sheet does not have a constant slope. 









Table Y. 









Slopes 



Air- 







Mean 





of 



equiva- 







ratio 



Sheets 



curves 



lents 



Ratio 



Vatomic wt. 



\ atomic wt. 



A Au__ 



032 



0-719 



2-24X10 1 







B Aii.. 



0-051 



0-980 



1-92X10 1 







C Au__ 



0-064 



1-375 



2-15X10 1 







D Au_. 



o-ioo 



1-900 



1-90X10 1 



14-05 



28-80 



A Sn__ 



0-032 



1-011 



3-16X10 1 







B Sn__ 



0-063 



1-995 



3-17X10 1 



10-91 



34-34 



A Ph.. 



0*053 



1-104 



2-08 X10 1 







B Pb_. 



0-071 



1-396 



1-96X10 1 







C Pb._ 



0-110 



2-325 



2-11X10 1 



14-38 



29-38 



A Al._ 



o-oio 



0-597 



5-97X10 1 







B Al_. 



0-020 



1-209 



6-04X10 1 







C Al._. 



0-033 



1-803 



5-48X10 1 



5-19 



30*41 



D AL. 



0-045 



2-672 



5-93X10 1 







A H... 



— 0-020 



0231 



1-16X10 1 







B H__. 



— 0-034 



0-428 



T17X10 1 



• 





C H... 



— 0-064 



0-762 



1-19X10 1 







For the thin sheet of aluminium the air-equivalent is almost 

 constant for the higher ranges or speeds, but as the speed of 

 the entering alpha particle decreases the air- equivalent decreases 

 slowly and in the lower ranges the decrease becomes quite 

 apparent. For the thicker sheets of aluminium the change is 

 more marked even for the higher ranges. The statements of 

 McClung, Levin and Rutherford that equal successive layers 

 of aluminium foil diminish the range of the alpha particles by 

 equal amounts seem to hold true for thin sheets of foil when 

 the range is high; but when the metal sheet is thicker, or for 

 thin sheets when the range is low, it does not hold. The 

 slight difference, however, in the air-equivalent of the thin 

 foil when near and far away from the polonium, would scarcely 



