﻿7 Radiation from Radium B. 307 



curve has been drawn on the assumption that all the rays 

 come from radium C and none from radium B. The 

 activity is proportional to N, the number of atoms of 

 radium C disintegrating per second which can be calculated 

 from the following equation : 



N = W*2 (X.-XJ -m-^Kk - Xi)' ' ' (1) 



A = 1,2,3,4 



where the number of atoms of emanation disintegrating per 

 second at the beginning is taken as unity and X 1? A 2 , X 3 , and \ 4 

 are the decay constants of the emanation, radium A, radium B, 

 and radium respectively. N reaches a maximum value 

 0*972 1 after 258 minutes. In drawing the curves in fig. 3, 

 this value has been taken as 100. 



The curve E, fig. ?>, has been plotted only for the first few 

 minutes, but the agreement between theory and experiment 

 is so satisfactory for the whole time during which the activity 

 of the emanation rises that the values of the activity at 

 different times can be taken from column II. of the Table 

 given in the appendix. In the third column of this table are 

 given the numbers calculated on the assumption that 11'5 

 per cent, of the ionization is due to radium B and the rest to 

 radium C, when radium B and radium C are in radioactive 

 equilibrium. The curve obtained on this assumption is 

 plotted in fig. 3, curve F. The experimental points obtained 

 when measuring through the walls of the ordinary 7-ray 

 electroscope mentioned above agreed well with this assumption, 

 and the points obtained in this case are marked in fig. 3 with 

 circles. This curve is similar to that given by Rutherford * 

 in his Bakerian Lecture, p. 199, which was obtained, from 

 measurements taken through a considerable thickness of 

 matter. The difference from the curve, calculated on the 

 assumption that radium B is rayless, is therefore no doubt 

 due to the emission of 7 rays by radium B and not to the soft 

 f3 radiation emitted by it as has sometimes been supposed. 



The agreement between theory and experiment when 

 measuring through 2'3 cm. of lead indicates that the amount 

 of hard 7 radiation from radium B compared with that from 

 radium C is extremely small. There can be no doubt that 

 if such radiation exists the ionization produced by it through 

 2*3 cm. of lead does not amount to 1 per cent, oi' thai 

 produced by radium C, if the decay constants assumed are 

 correct. 



* Rutherford, Phil. Trans. A. 204 (1904). 



