CHAPTER VI. 



THE DECAY OF IONIZED NUCLEI IN THE LAPSE OF TIME. 



71. Introduction. The attempt was made in an earlier paper to 

 standardize the coronas by aid of the decay curves of radium. The 

 method is apparently very simple and requires the knowledge merely of 

 the coronas appearing under given circumstances when the radium tube 

 is in place d on the outside of the fog chamber, in comparison with the 

 coronas observed under the same circumstances when the radium has 

 suddenly been removed for different lengths of time before condensation. 

 From electrical observations the equation 



dn/dl=bn 2 or i/ = i/n' + b (tt'} 



is found to be adequate if n and n' denote the ionizations occurring at 

 the times t and t', and the same would appear to be the case with the 

 corresponding nucleations. Moreover, if the relative nucleations n'/n for 

 two coronas obtained at a given exhaustion are known (for instance by 

 the above method of geometric sequences) the absolute values of the 

 nucleations will follow. With a radium ionization at t and t f seconds 

 after its removal 



But the attempt to carry out this apparently straightforward method 

 leads to grave complications. If n be reckoned in thousands per cubic 

 centimeter, the electrical value of b may be taken as 6 = 0.0014, while 

 the value of b found from the decay of ions is more than two times as 

 large as this, increasing, moreover, very rapidly as the nucleation is 

 smaller. True, it is possible that the above method for finding the 

 nucleations absolutely may be at fault. Relative values seem to be 

 trustworthy, but absolute data are not to the same degree substantiated; 

 but even if this were granted, the march in the values of b would be 

 unaccounted for and seems to be a new phenomenon. 



72. Data. Exhaustion above the fog limit of air. In table 50 the 

 adiabatic drop of pressure dp a is somewhat larger than the fog limit 

 of dust-free air, as is shown in the second section of the table. The 

 column 5 gives the angular diameter of the coronas at a time / in seconds 

 after the sudden removal of radium from the outer walls of the glass fog 

 chamber. The relative drop in pressure x = dp 3 /p and the nucleations 

 n follow. The initial coronas are small, as the radium is weak (10,000 X , 

 100 mg.). 



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