T. S. Taylor— Retardation of "Alpha Bays." 173 



In figure 3 

 tion of 



curves I and II represent parts of the top por- 

 two Bragg curves* as obtained when a sheet of gold 

 foil was kept at a distance of 6 mm from the polonium. Curve 

 I was plotted from readings taken at the end of the first 

 minute and curve II from readings taken at the end of the 

 second minute. The curves being plotted with magnified 

 ordinates have much greater slopes than they would have if 

 plotted on the ordinary scale. 



The polonium, with the gold foil 6 mm above it, was then set 

 at a distance of 3*0 cm from the ionization chamber. As can be 

 seen from curves I and II, this distance was such that the 



31 



3-0 



2-9 



2-85 

 2-5 



0-5 



F> 



X 



V 























































I 





























































































DL 





































































Fig. 3. The ordinates of curves I and II are the distances in centimeters 

 of the polonium from the ionization chamber. The ordinates of III and IV 

 are the distances in centimeters of the sheet of gold from the polonium 

 ■when the polonium was kept at a distance of 3"0 cms from the ionization 

 chamber. The abscissas of I and III are the deflections in centimeters of 

 the electrometer needle at the end of the first minute, and the abscissas of II 

 and IY are the deflections at the end of the second minute. 



deflections obtained corresponded to two points in the slightly 

 inclined (top) portions of the Bragg curves. With the polo- 

 nium at this distance of 3'0 cm from the ionization chamber, the 

 gold foil was moved away from the polonium towards the 

 ionization chamber, and the ionization was measured when the 

 sheet was at various distances from the polonium. It was 

 found that the ionization increased as the distance of the gold 

 sheet from the polonium increased. 



In figure 3, curves III and IY were plotted with the deflec- 

 tions of the electrometer needle at the end of the first and sec- 

 ond minutes respectively as abscissas, and with the distances 



* This is the portion of the ionization curve which, as ordinarily plotted, 

 is nearly horizontal. 



