IX, A, 1 



Wright and Smith: Radium Emanation 



63 



Table V.— 



rests for radium in the coconut charcoal. 









Electro- 

 scope 

 reading in 

 divisions 

 per minute 

 due to gas 

 from char- 

 coal. 



Deflection 



Emanation 



Date. 



Period 

 of rest. 



Natural 

 leak of 

 electro- 

 scope. 



due to em- 

 anation 

 generated 

 by charcoal 

 in period of 

 rest. 



accumu- 

 lated 

 per day 

 expressed 

 in divisions 

 per minute. 





Days. 











Oct. 12,1912 



4.0 



0.032 



0.019 



—0. 013 



—0.004 



Jan. 2. 1913 



5.75 



0.023 



0.031 



0.008 



0.002 



Jan. 2, 1913 



9.2 



0.024 



0.024 



0.000 



0.000 



June 9,1913 



74.0 



« 0.077 



0.067 



0.010 



0.002 



June 16, 1913 



81.0 



0.016 



0.036 



0.020 



0.003 



June 17, 1913 



36.0 



0.016 



0.031 



0.015 



0.002 



June 19, 1913 

 Mean 



38.0 



0.016 



0.031 



0.015 



0.002 



0.0004 













' The electroscope had just been set up, and the insulation leak was still large. 



Table V shows that if there is any radium in the charcoal the 

 amount is too minute to be detected by a sensitive electroscope. 

 Since the deflection of the aluminium leaf was extremely slow, the 

 readings were confined to one or two divisions, which increases 

 the probability of a comparatively large observational error. 

 The natural leak recorded was generally taken immediately 

 before the observation on the gas driven off from the charcoal 

 and as far as possible over the same part of the scale. 



RADIUM-EMANATION CONTENT OF THE ATMOSPHERE 



The theory upon which the calculations of the radium-emana- 

 tion content of the atmosphere are based has been given at 

 length by several writers on the subject. It can, however, be 

 very simply deduced in the following manner : 



If A represents the radioactive constant of radium and T the 

 duration of exposure, then A T will be the emanation produced 

 by 1 gram of the radium in the time T. 



Now, if we assume that the emanation is removed from the 

 solution of radium bromide as rapidly as it is formed, the 

 decay factor will not enter into the calculations since the rate 

 of decay of the emanation collected from the solution of radium 

 is the same as that for the emanation from the air. 



Therefore, if M is the amount of radium in radioactive equi- 

 librium with the emanation in 1 cubic meter of free air and 

 M' the number of grams of radium in the solution, then 



MV _d 

 M'XT~di 



where V is the total volume of air tested, d is the electroscope 

 reading due to the emanation from V cubic meters of air, and 



