454 Prof. E. Rutherford on the Origin of 



a photographic plate, a number of sharply marked bands are 

 observed, indicating that the rays are complex and consist 

 of a number of homogeneous groups of rays, each of which 

 is characterized by a definite velocity. 



This complexity of the radiation is best shown by those 

 products which emit penetrating ft rays and intense 7 rays; 

 for example, each of the products thorium JD and meso- 

 thorium 2 emits a number of well defined groups of ft rays 

 and penetrating 7 rays. The complexity of the ft rays is, 

 however, most markedly exhibited in the case of the products 

 radium B and radium 0, when a very strong source of 

 radiation is employed. Using as a ft ray source a thin- 

 walled glass tube containing a large quantity of radium 

 emanation, Danysz found that radiumB and radium C together 

 emitted about 30 groups of homogeneous rays. 



Notwithstanding this great complexity of the ft rays from 

 these products, general experiment has shown that the 

 number of ft particles emitted by them is about that to be 

 expected if each atom in breaking up emitted only one 

 ft particle. This important point has been carefully examined 

 by H. Moseley*, who has shown that not more than 2'13 

 ft particles are emitted during the disintegration of one atom 

 of radium B and one atom of radium 0. By separating 

 these two products. Moseley found that the atom of each 

 product contributes about half of this number. It thus seems 

 clear that on an average one atom in disintegrating emits 

 about one ft particle. 



In addition to the well-known ft ray products, Baeyer, Halm 

 and Meitner have shown by the photographic method that 

 radium itself and radium D emit a weak ft radiation which 

 consists in each case of two definite groups of ft rays. In 

 these cases, no evidence of the emission of a 7 radiation has 

 yet been observed. 



There appears to be no doubt that the 7 rays from active 

 matter are closely connected with the ft rays, and that both 

 types of rays arise in the transformation of the same atom. 

 Investigation, however, has shown that there is not any 

 obvious relation between the relative intensity of the 

 ft and 7 rays which are emitted from a given product. The 

 products radium C, thorium D, and mesothorium 2 emit 

 ft and 7 rays of about the same penetrating power and in 

 about the same relative proportion. On the other hand, 

 uranium X, which emits penetrating ft rays, gives relatively 

 few 7 rays. A still more striking instance is the ft ray 



* Moseley. "The number of /3 particles emitted in the transformation 

 of radium." ' Read Roy. Soc. June 13, 1912. 



