the X Radiation from a Coolidge Tube. 



161 



energy of motion of each of these groups of electrons have 

 been measured by Rutherford and Robinson *, and the more 

 intense groups (labelled with letters in the original paper) 

 are given in the following table: — 





(3 rays from Radium 



B. 



i 



j3 rays from 



Radium 



C. 



Group. 



Intensity. 



Energy 

 -rl0 13 e. 



Voltage(volts). 



Group. 



Intensity. 



Energy 

 -=-10 13 e. 



Voltage(volts). 



A 



s. 



3-332 



333,200 



A 



m.f. 



21-02 



2,102,000 



B 



v.s. 



2-610 



261,000 



B 



m.f. 



1751 



1,751,000 



C 



v.s. 



2-039 



203,900 



C 



m. 



16-71 



1,671.000 



D 



T.S. 



1-519 



151,900 



D 



m. 



14-09 



1,409,000 



E 



s. 



•503 



50,300 



E 



m.s. 



13-28 



1,328,000 



F 



v.s. 



•376 



37,600 



F 



m. 



11-49 



1,149,000 











G 



m.s. 



10-31 



1,031,000 











H 



m.s. 



5-94 



594,000 











K 



s. 



516 



516,000 











L 



m. 



2-96 



296,000 











M 



m. 



2-59 



259,000 











N 



m. 



1 81 



181,000 



The column headed " voltage " gives the potential difference 

 in volts between which the electron must move to acquire 

 the observed energy. 



Apart from the low-velocity groups L, M, N, the ft rays 

 from radium C consist mainly of groups lying between 

 500,000 and 2,000,000 volts. This is about the same range 

 of voltage as we estimated to excite the penetrating gamma 

 rays from consideration of the absorption of X rays and 

 gamma rays by aluminium and lead. It would thus appear 

 probable that the observed groups of ft rays are due to the 

 conversion of the energy, E = Az/, of a wave of frequency v into 

 electronic form, and that consequently the energy of the 

 yS-ray groups may be utilized by the quantum relation to 

 determine the wave-lengths of the penetrating gamma rays. 



Such a conclusion is borne out by consideration of the 

 groups of rays from radium B. 



H. Richardson f has determined the absorption of these 

 rays by lead, and concluded that they could be analysed 

 approximately into three component groups for which the 

 absorption coefficients, fi, in lead were 45, 6, and 1*5 cm. -1 

 respectively. From the observations with a Coolidge tube, 

 the value, ^=6, should correspond to waves excited at about 



* Kutherford and Robinson, Phil. Mag. xxvi. p. 717 (1913). 

 t Richardson, Proc. Roy. Soc. xci. p. 396. 



