CONTEMPORARY ADVANCES IN PHYSICS 



85 



There is an interesting and important relation between the initial 

 speeds of alpha-rays and the half-periods of the substances which emit 

 them. One varies as an exceedingly high (negative) power of the 

 other, so that when speed is plotted versus half-period upon logarithmic 

 plotting-paper the resulting curve is a straight line; or, rather, three 

 parallel straight lines, one for each of the three series. This remains 

 true if we plot any power of the speed (for instance, the third) against 

 ?8.0 



2Q>.0 

 ?4.0 

 Z2.0 

 20.0 



18.0 



O 



•^ Ifc.O 



2 14.0 



I 



12.0 



10.0 



8.0 



fc.O 



4.0 



20 



0.4 



0.5 



fc 



0.7 



0.8 



,Rr 



l-Og,o' 



Fig. 4. The Geiger-Nuttall relation 



Data for the uranium-radium series; the values for alpha-particle range denoted 

 by dots are taken from pleochroic haloes, those marked by crosses from experimental 

 data. The value of half-period for UII is not known, but is placed by interpolation 

 upon the smooth curve. The straight line represents the best attainable approxi- 

 mation by a linear relation between logarithms of half-period and range; the smooth 

 curve is that drawn by B. Gudden, from whom the data are taken. 



any power of the half-period (for instance, the power —1), so that the 

 logarithm of the range of the emitted particles varies linearly with the 



