﻿Growth of Radium C from Radium B. 301 



at the same time it should be remembered that the possible 

 errors made in deducing the coefficient from the observations 

 are relatively great. Having regard to these two facts the 

 agreement between the different values is perhaps as close as 

 can be expected. 



There is, however, one point of difference between our 

 results and those of Schmidt which is of importance, for our 

 experiments give no indication of any very soft ft rays of 

 coefficient 890 cm. -1 . According to Schmidt, RaB emits 

 such rays in quantity sufficient to produce an ionization 

 whose magnitude is about 12 per cent, of that produced by 

 the a rays emitted by the RaC in equilibrium with it. This 

 radiation should have been detected in our experiments if it 

 existed ; for when measuring without any aluminium screen, 

 the rise curve should have risen from about 25 per cent, of 

 the maximum instead of from 3 per cent, as shown in figure 3. 

 The cause of the difference between our results and those of 

 Schmidt is being investigated by one of us. 



It should also be pointed out that Schmidt finds for the 

 ratio or the hard rays from RaB to those from RaC the value 

 10 per cent., whereas we find only about 4*5 per cent., since 

 the curves (fig. 3) for thicknesses greater than '7 mm. rise 

 from about 10 per cent, of the maximum. The smallness of 

 the ratio of the hard /3 radiation compared with that of RaC 

 is very striking and involves interesting possibilities, but it 

 would be premature to discuss these on the available 

 experimental evidence. 



Summary. 



(1) The a rays as well as the greater part of the /? rays 

 from RaC belong to RaC!. 



(2) The ionization of the /3 rays from RaC 2 compared 

 with that of the rays from RaCj is so small that it could not 

 be detected in these experiments. This confirms the view 

 that RaC 2 is not in the direct radioactive series but is formed 

 as a side product. 



(3) The /3 rays from RaB fall into two groups whose 

 coefficients of absorption are respectively 13 cm." 1 and 

 91 cm. -1 . The ionization produced by the former amounts to 

 only about 1^ per cent, of the whole ionization due to RaB. 



(4) No evidence could be found of the existence of rays 

 from RaB whose coefficient is 890 cm. -1 . 



Our thanks are due to Professor Rutherford for supplying 

 us with the necessary emanation and for the interest which 

 he has taken in the progress of the experiments. 



