﻿produced by an Alpha Particle from Polonium. G75 



Determination of Alpha Particles in Beam. 



The plug containing the polonium, with the cap for 

 limiting the beam of rays over it, was removed from the 

 apparatus and the number of alpha particles emerging in the 

 beam determined by counting the number of scintillations 

 produced per minute upon a zinc sulphide screen. A zinc 

 sulphide screen purchased of Harrison Glew of London, and 

 a microscope, composed of a Leitz objective number " 4 n 

 and a Leitz eyepiece number '* 0, w were used in the counting 

 of the scintillations. The screen was standardized by using 

 a small quantity of the active deposit of radium emanation 

 for which the alpha ray activity was calculated from the 



Table IL 



Corrected 



deflexion 



corresponding 



to total 



ionization. 



Potentials in 

 E.S.U. corre- 

 sponding to 

 deflexions in 

 column 1. 



Charge that 

 would be given 



to plate " A " 



by entire beam 



used.. 



Number of 



particles 



entering 



pb a ruber in 



5 minutes. 



Ions pro- 

 duced by- 

 single alpha 

 particle. 



17-20 



1606 

 16/62 

 1616 



15-80 



7'55xl0^ 4 

 745 Xl0~ 4 

 7-30 XlO- 4 

 7'10 Xl0~ 4 

 6-94X10" 4 



4'15xl0- 2 

 4-09x10-2 

 4-01x10-2 

 3-90 XUT 2 

 3-82X10- 2 



547 

 ,536 

 520 

 509 

 503 



163,000 

 164,000 

 165,000 

 165,000 

 163,000 





Me? f 



n value of ions p 



roduced... 



164,000 



gamma ray activity. By this process it was found that 

 86 per cent, of the alpha particles striking the screen pro- 

 duced scintillations that were readily counted. A large 

 number of determinations of the number of scintillations 

 produced was made for each separate determination of the 

 ionization current. The mean value of each series of these 

 determinations was then corrected to take account of the 

 fact that only 86 per cent, of the alpha particles striking 

 the screen produced scintillations. These values were then 

 multiplied by 5 in order to get the total number of alpha 

 particles that entered the ionization-chamber during the time 

 required to make one observation of the ionization current. 

 This mean value of the number of alpha particles entering 

 the ionization-chamber is recorded in column 4, Table IL, 

 for each determination. 



2 Y 2 



