Taylor —Retardation of Alpha Rays ~by Metals. 363 





Table 



III. 





Range of the 









a-particle upon 









entering the 









hydrogen 



A hydrogen 



B hydrogen 



C hydrogen 



5'2 



0-231 



0-428 



0-762 



4-8 



0-235 



0-434 



0-776 



4-4 



0-241 



0-442 



0-791 



4-0 



0-247 



0*451 



0-807 



3*6 



0-254 



0-460 



0*831 



3-2 



0-262 



0-470 



0-861 



2-8 



0*271 



0-483 



0-896 



2'4 



0-283 



0-499 



0-938 



The reason the maximum range here is 5'2 cms instead of 

 5*7 cms , as it was in Table II, is because the air-equivalent of the 

 lower film of celloidin must be subtracted, since the alpha 

 particles must pass through it before entering the hydrogen. 

 The air-equivalent of the lower film was 0*5 cms . 



Although the air-equivalents of the celloidin sheets remained 

 constant, it seemed probable, from the behavior of the hydrogen 

 sheets, that if the same experiments were performed in an 

 atmosphere of hydrogen, the .hydrogen-equivalent* of the 

 celloidin sheet would not remain constant, but would decrease 

 as the range of the alpha particles decreased. To investigate 

 this point the apparatus was enclosed in an air-tight sheet 

 iron case, which by several partial evacuations and refillings 

 could be filled with practically pure hydrogen. With polonium 

 as the source of rays the hydrogen-equivalents in centimeters 

 of sheets of celloidin, aluminium, tin, and gold were deter- 

 mined for various distances of the sheets from the polonium. 

 Only the results for the celloidin and A gold are given in 

 Table IV, as they are sufficient to illustrate the point in question. 



Table IV. 



Range in H of en- 

 tering particle .. 



Celloidin 



A Gold 



13-0 

 23-20 



27-97 



12-6 12-2 

 23-08 22-96 

 27-55J27-11 



11-8 



22-80 



26-67 



11-4 11-0 

 22-64 22-48 

 26-2325-75 



10-6 



22-32 



25-17 



10-2 



22-16 



24-49 



9-8 

 21-88 

 23-91 



9-4 

 21-60 

 2301 



The curves in figure 1 represent the results recorded in 

 Tables II, III, and IV. By noting the slopes of the curves 

 some comparison of the rates, at which the air-equivalents of 

 the various sheets change, can be obtained. Taking the 

 general slope of each curve and dividing it into the air- 

 equivalent of the corresponding sheet when 0*9 cms from the 

 radium, it is found that for a given metal the quotient thus 



* The hydrogen-equivalent is the amount by which the range of the a- 

 particles in hydrogen is cut down by their passage through the sheet. 



