316 



Sir E. Rutherford on the 



radioactive atom have a very similar spectrum to that 

 observed for the J3 rays excited by y rays, indicating that 

 both have a similar origin. 



ft-ray spectrum from radium B. 



We shall now consider the /3-ray spectrum of radium B 

 for which the energies of the groups of J3 rays have been 

 carefully determined by Rutherford and Robinson. The 

 results are included in the following table. Column I. gives 

 the number of the line, II. the intensity, III. the ratio ft of 

 velocity of the /3 particle to the velocity of light, IV. the 

 energy of the j3 particle composing each group, and V. the 

 suggested unit and its multiple. 



I. 



II. 



III. 



IV. 



i 



No. 



Intensity. 



(3. 



Energy 

 -^10 13 e. 



Unit of energy 



vlO ,3 C. 



1 



f. 



•823 



3-852 



5X-770 



2 



m.s. 



•805 



3-480 



4x-870 



3 



s. 



•797 



3 332 



7X-476 or 6x555 



4 



v.f. 



•787 



3460 



5x-632 



5 



m.s. 



•762 



2-758 



5X'552 



6 



v.s. 



•751 



2-610 



3X-870 



7 



m. 



•731 



2-366 



5X-473 



8 



m.s. 



•719 



2-228 



3 X -743 or 4 X "557 



9 



v.s, 



•700 



2-039 



4x 510 or 6 X -373 



10 



m.s. 



•656 



1-650 



4x-412or3x-550 



11 



v.s. 



•635 



1-519 



2X'760 or 3 X '506 



12 



m. 



— 



— 



— 



13 



m. 



— 



— 



— 



14 



m.s. 



•426 



•539 



lX-539 



15 



s. 



•414 



•503 



lX'503 



16 



v.s. 



•365 



•376 



1 X '376 | 



1 



It is certainly striking that the energies of the three 

 strong groups of j3 rays 14-16 agree very closely with the 

 calculated values for the reflexion angles of the y rays for 

 the lines at 2° 20', 2° 28', and 3° 18', which gave energies 

 •537, -507, -379xl0 13 e respectively. When there are so 

 many lines as in the 7-ray spectrum of radium B, and 

 uncertainty as to whether some of the lines are to be ascribed 

 to radium B or to radium C, it is obvious that it is difficult 

 to fix with certainty the unit in which to express the energies 

 of the groups. It is noticeable, however, that the strong- 

 lines 2 and 6 are expressed by small integral multiples of 

 *870 X 10 13 e, which agrees fairly well with the energy to be 



