Energy of a particles from Radioactive Substances. 113 



by the a particle. The results, expressed in this form, do 

 not involve any assumption as to the actual value of e. 



The ranges of the a. particles from all the various substances 

 except uranium have been determined by the electrical 

 method, first employed by Bragg and Kleeman. On account 

 of the feeble activity of uranium, experiments made to 

 determine the range of its a particles by the same method 

 have not yet been successful. Bragg h;is. however, deter- 

 mined the stopping power of the a particle from uranium in 

 terms of aluminium, and from this it can be deduced that 

 the range of the a particle from uranium is in the neighbour- 

 hood of 35 cms. 



It is of interest to compare the average velocity and energy 

 of the a particle expelled in the successive transformations of 

 the radioelements. The results are tabulated below. The 

 third column gives the total energy of motion of the a par- 

 ticles liberated as a result of the successive disintegrations of 

 a single parent atom. Since for any primary element in 

 equilibrium with its succeeding products, the same number 

 of atoms of each product break up per second, the average 

 velocity or average energy of the a particles for each of the 

 families of products is given by the sum of the velocities or 

 energies divided by the number of products concerned. 



Table II. 



Element, 



Total energy liberated 

 Average Telocity Average energy as the result of 

 of a particles in of a particles successive disiutegra- 

 cins. per second I in ergs. tions of one atom of 



parent matter. 



Uranium . 



Radium (including 1 

 radium F) J 



Radium (excluding 

 radium F) 



About 

 1-56 xlO 9 



T74 ., 



Uranium (including 

 radium and all its; 

 products) 



Thorium . 

 Actinium. 



1-77 



1-71 



1-88 



1-88 



2-41xlO u .e 



302 ,, 



3-12 



2 # 92 



3-54 

 3-51 



2-41 X 10 1 

 lo-l „ 



12-5 „ 



17-5 „ 



177 „ 

 140 „ 



Phil. Mag. S. 6. Vol. 13. No. 73. Jan. 190; 



