PRESENT PROBLEMS IN RADIOACTIVITY. 15 



Product. T Radiations. 



Radium, a rays. 



Emanation, 4 days, a rays. 



Radium A, 3 mins., a rays. 



Radium B, 21 mins., no rays. 



Radium C, 28 mins., a, /3 and 7 rays. 



When the emanation has been left in a closed vessel for several 

 hours, the emanation and its successive products reach a stage of 

 approximate radioactive equilibrium, and the heating effect is then 

 a maximum. If the emanation is suddenly removed from the tube by 

 a current of air, the heating effect is then due to radium A, B and 

 C together. On account, however, of the rapidity of the change of 

 radium A (half value in three minutes) it is experimentally very 

 difficult to distinguish between the heating effect of the emanation and 

 that of radium A. The curve of variation with time of the heating 

 effect of the tube after removal of the emanation is very nearly the 

 same as the corresponding curve for the activity measured by the a 

 rays. These results show that each of the products of radium supplies 

 an amount of heat roughly proportional to its a ray activity. Each 

 product loses its heating effect at the same rate as it loses its activity, 

 showing that the mission of heat is directly connected with the radio- 

 active changes. The results indicated that the product, radium B, 

 which does not emit rays, does not supply an amount of heat com- 

 parable with the other products. This point is important and requires 

 more direct verification. 



Since the heat emission is in all cases nearly proportional to the 

 number of a particles expelled, the question arises whether the bom- 

 bardment of these particles is sufficient to account for the heating 

 effects observed. The kinetic energy of the a particle can be at once 

 determined, since e/m and v are known. 



The following table shows the kinetic energy of the a particle de- 

 duced from the measurements of Eutherford and Des Coudres. The 

 third column shows the number of a particles expelled from 1 gram 

 of radium per second on the assumption that the heating effect of 

 radium (100 gram calories per gram per hour) is entirely due to 

 the energy given out by the expelled a particles. 



Number of Particles 

 Observer. Kinetic. expelled per Second 



from 1 Gram of 

 Radium. 

 Rutherford 5.9 X 10-« ergs 2 X 10 u 



Des Coudres 2.5 X 10~ 6 ergs 5 X 10 11 



This hypothesis that the heating effect of radium is due to bom- 

 bardment of the a particle can be indirectly put to the test in the 

 following way. It seems probable that each atom of radium in break- 

 ing up emits one a particle. On the disintegration theory, the residue 



