360 Taylor — Retardation of Alpha Rays by Metals. 



of the top, or slightly inclined portion, of the Bragg ioniza- 

 tion curve due to the a-particles from radium C fell within 

 the chamber, and the air-equivalents of the various metal 

 sheets determined at various points in the path of the rajs in 

 exactly the same manner as that used in the first experiments.* 

 The rays of shorter range than those of radium C had no 

 effect upon the results since they did not reach the ionization 

 chamber. Beta and gamma rays are also given off by the 

 radium bromide, but the ionization produced by them can be 

 considered as a constant value over the part of the path used 

 and consequently the effect due to them is only a shifting of 

 the curves to the right parallel to themselves, which would 

 have no effect upon the results under consideration. 



In Column 1, Table I, are given the different metal sheets 

 used in the experiments. Column 2 contains the thickness in 

 centimeters of the respective sheets. Column 3 has the air- 

 equivalents of the sheets as measured directly when the sheets 

 were nearest the source of rays. Column 4 contains the ratios 

 of the air-equivalents to the thickness of the respective metals. 

 The last three lines of the table will be referred to later. 

 The air-equivalents of the sheets given in Column 1, Table I, 

 as determined by an improved method for any position of 

 this sheet, are given in Table II. 



The aluminum foil over the radium to prevent the escape of 

 the emanation cut down the range of the a-particles 0'46 cm . 





Table 



I. 





I 



II 



Ill 



IV 



Metal 



Thickness 



Air- equivalent 





Sheets 



in cms. 



in cms. 



Eatio 



A Au 



1-27 X10- 4 



0*719 



5-67X10 3 



B Au 



1-74X10- 4 



0-980 



5-63 X 10 s 



C Au 



2-50X10- 4 



1-375 



5-50X10 3 



D Au 



3-50X10- 4 



1-900 



5-42X10* 



A Sn.__ 



3-86 X10- 4 



1-011 



2-61X10 5 



B Sn 



7-99X10- 4 



1-995 



2-48 X10 3 



A Pb 



2-84X1CT 4 



1-104 



3-88X10 3 



B Pb 



411X10- 4 



1-396 



3-40X10 3 



C Pb.. 



6-95 X10- 4 



2-325 



3-34X10 3 



A Al _. 



3-30 X10- 4 



0-597 



1-79X10 3 



B Al 



6-77 X10- 4 



1-209 



1-79X10 3 



C Al. 



10*40 X10- 4 



1-803 



1-73X10 8 



D Al 



16-10X10- 4 



2-672 



1-66X10 3 



[ydrogen Sheets 









A hydrogen.. 



1*07 



0-231 



2-15X10- 1 



B hydrogen.. 



1-93 



0-428 



2-21 XIO -1 



C hydrogen.. 



3*23 



0-762 



2-36 X10 _1 





* Loc. cit., pp. 



173-175. 





