612 Ions produced from Radioactive Substances. 



radium. In the experiments of Makower the value obtained 

 for the charge was considerably greater than would be expected 

 if Ra emits only one ft particle. 



The average value of the number of ions produced by a 

 ft particle of high speed per centimetre of path at atmospheric 

 pressure is 67. This value is considerably smaller than that 

 given by Durack * which is 127. In Durack's experiments, 

 however, reflexion of the ft rays was not taken into account ; 

 this reflexion increases the ionization current and decreases 

 the charge which is received by the plate, and gives a measure 

 of the number of ft particles. Both these factors, if taken 

 into account, would decrease the number of ions produced by 

 one ft particle. 



Concerning the soft radiations, we have already pointed out 

 the difficulties of obtaining reliable values for the number of 

 ions produced. There can, however, be no doubt, as is shown 

 in the table, that with the exception of thorium A, the number 

 is very much smaller than for the penetrating radiations. 

 This may, of course, be due to a rapid decrease of the ionizing 

 power of the ft rays with decreasing velocity, or it might be 

 possible that the soft radiations are due to products which are 

 not in direct line of transformation. Such a possibility is sug- 

 gasted by the recent experiments of Fajansf? which brought 

 out the existence of a side product in the radium series. So 

 far as thorium A is concerned, our value for the ionization 

 compared with that of thorium D is higher than that of Halm 

 and Meitner J; but this is accounted for by the experimental 

 arrangement. The recent experiments of v. Baeyer, Hahn, 

 and Meitner § indicate a complexity of the rays from 

 thorium A, as shown by photographs. 



Summary. 



The relative number of ions produced by the ft particles from 

 the different radioactive products was determined. In each 

 case the number of atoms of the ft ray- substance breaking 

 up was found from the number of a particles emitted by an 

 a-rays product in radioactive equilibrium with the /3-ray 

 substance. 



The results could best be explained by assuming that Act C, 

 Th C, RaB, and perhaps also Ra C emit two ft particles, 

 or consist of two successive /3-ray products emitting similar 



* J. J. E. Durack, PHI. Ma?, v. p. 550 (1903). 



+ K. Fajans, Phys. Zeits. xiL p. 369 (1911). 



% 0. Hahn and L. Meitner, Phys. Zeits. ix. p. 321 (1908). 



§ Loc. cit. 



