ON THE IONIZATION DUE TO THE EMANA- 

 TION OF RADIUM' 



By William Duane 



If radium emanation is introduced quickly into a suitable testing 

 vessel, the saturation current that can be made to pass through the 

 air contained in the vessel increases rapidly during the first ten min- 

 utes, then more slowly, and attains a maximum value at the end of 

 about three hours. Theoretically, the relation between the current i 

 and the time i, counted from the moment the emanation enters the 

 vessel, should be of the form 



i=A+B}(t). (i) 



The second term corresponds to the progressive production of the 

 induced radio-activity. A and B depend upon the form of the testing 

 vessel and upon the quantity of emanation employed; they remain 

 constant as long as the emanation has not diminished perceptibly. 

 Using the expression for /(/) given by MM. Curie and Danne^ we 

 may write : 



_ i=i \ «-^ [^^-"^(,4, h'-'' - ^ ^,^"0 ] } (2) 



with the conditions: 



The constants b and c are known very accurately. In order to 

 determine the two ratios «/^ and ^/fj-, the saturation currents were mea- 

 sured in suitable testing vessels by means of an electrometer and a 

 piezo-electric quartz, the readings being taken each minute during the 

 first ten minutes and thereafter less frequently. The following table 

 contains the observed currents, and those calculated from equation (2), 

 using the values 



a=.oo4oi &=.ooo538 c=.ooo4i3 ig =43.1 



a=2.37 ^=1-37 ^='57° /^=.438 



and the second as the unit of time. 



lAn account of the experiments described in this article was presented to the French Academy on 

 February 27, igos. The experiments were made in M. Curie's Radium Laboratory. 

 ^Comptes Rendus, March 14, 1904. Qt 



