550 



) 



W. E. Barss- 



-Measurements of Radio-activity. 



V 



c, 



c, 



c 3 



C 4 C 5 



2 



•72 



•55 



•40 



•23 -16 



4 



1-60 



1*15 



•85 



•50 -38 



8 



2*50 



1-90 



1'40 



•80 -55 



16 



2-90 



2-20 



1-50 



•96 -65 



40 



3-35 



2-40 



1-75 



1-05 -75 



80 



3*53 



2-58 



1-86 



1-10 -78 



200 



3-65 



2'80 



1-95 



1-16 -80 



400 



3-80 



2-90 



2-05 



•83 



600 



3-90 



3-00 



2-08 





A series of curves plotted from these data is given in fig. 1: 

 abscissae represent the potential Y applied to the case. Curve 

 1 has for its ordinates the values s;iven in C, above, curve 2 the 



value 



s in C„, etc. 



Katios of ionization currents are given in the following table: 



V 



0,/C, 



Ci/C 3 



C:/C 4 



C/C 



2 



1-31 



1-80 



3-13 



4-50 



4 



1-39 



1-88 



3-20 



4-21 



8 



1-31 



1-80 



3-12 



4-54 



16 



1-32 



1-93 



3-02 



4-45 



40 



1-39 



1-91 



3-19 



4-46 



80 



1-36 



1-89 



3-21 



4-52 



200 



1-30 



1-87 



3-14 



4-56 



400 



1-31 



1-85 





4*57 



600 



1-30 



1-87 







It is evident that the current ratios are constant within the 

 limits of experimental error. 



In the above data the potential applied to the case was nega- 

 tive. A series of readings was made with the potential posi- 

 tive giving similar results. 



The radium emanation used was drawn from carnotite, 

 the amount of emanation being equivalent to the amount in 

 equilibrium with about 10" 8 gm. of radium. It remains to 

 be tried to what degree the intensity may be increased before 

 there is a change in the current ratios. 



Summary. 



"When the a-particles are moving in all directions with 

 respect to the electric field, and when the source of ionization 

 is not too intense, the ratio of the currents obtained from two 

 sources of different intensities is constant for different poten- 

 tials applied to the ionization chamber. 



No great errors are involved even when currents are used 

 Jess than one-fifth of the saturation value. 



In conclusion, I want to thank Professor Bumstead for his 

 many suggestions throughout the experiment. 



Sloane Physical Laboratory, Yale University, New Haven, Conn. 



