Velocity of the a particle on the Stopping Power. 513 



Distance from 



I. 



II. 



III. 



radium to 



An next 



Al next 



Au next 



ionization chamber. 



radium. 



radium. 



radium. 



20 



598 



637 



616 



21 



564 



614 



584 



22 



509 



576 



514 



23 



440 



505 



435 



24 



340 



426 



347 



2-5 



271 



364 



268 



26 



194 



267 



196 



2-7 



132 



185 



140 



2-8 



91 



128 



96 



29 



68 



94 



69 



3-1 



48 



57 



50 



33 



44 



47 



3S 



3-5 



38 



43 



37 



Fig. 4. — Showing that the stopping-power of a pair of metal sheets 

 Au and Al is altered by inverting the sheets. 



«K 















>• 

 ■5 



X 





ctppt 



Lowe 



7* curve /It 

 r curve /I i 



next fta,. 

 i next ftct. 















x • 



X 

















In another experiment, in which the Al was equivalent to 

 about 3*2 em. and the gold consisted of the 28 foils already 

 referred to, and equivalent to about 1 cm. of air, the average 

 range of the a. particle of RaC after passing through Au first 

 and Al afterwards w T as 2*575, whereas when it passed through 

 the metals in the inverse order it was 2*655. In this case 

 there was therefore a drop of *08 cm. 



It is of course a differential effect that is observed in these 

 cases. When the Au is placed above the Al it is equivalent 

 to taking it nearly 3 cm. further away from the radium, 

 making, that is to say, the same difference between the 

 velocities of the a particles used in the two cases as exists 

 between the velocities of the particles of Ra and RaC. Now 

 it has already been stated that this set of gold-foils cut down 



Phil. Mag. S. 6. Vol. 13. No. 76. Apt il 1907. 2 N 



