700 Mr. E. Marsden and Dr. P. B. Perkins on the 



Scheme of Transformation. 



By analogy with the transformations in the active deposits 

 of thorium and radium, the actinium active deposit may be 

 written as follows: — 



a (5.7) a (6.5) /3y -a (5.4^* Act. I) — +? 



Act.Em^Actr! -*Ac<B -*Act.C «™* 4-71 mms.. 



3.9 sees, ,002 sec. .36.1 mins. j8(ft ^>Act#V— »? 



2.15 mins. .005 sec.(?) 



L e. we may suppose that *9985of the atoms of actinium C 

 emit a particles of range 5*4 cm. and become transformed into 

 atoms of actinium D, while the other *0015 may be supposed 

 to emit /3rays and produce the new product C 2 , whose period, 

 assuming Geiger's formula to be applicable, ought to be 

 about 1/200 second. 



On such an hypothesis, actinium C( = C 1 + C 2 ) may be 

 presumed to emit practically no B radiation compared with 

 actinium D. Experiments were made to test this point. 

 Pure actinium C 3 without B or D, was deposited on nickel 

 from hot acid solution, and the subsequent variation of activity 

 measured by fi rays. The curve rose from zero, showing 

 initially that no detectable /3 radiation was present compared 

 with that due to actinium D. 



It is of interest to compare the characteristics of the 

 products of the three active deposits, for they appear so 

 analogous that such a comparison might throw light on the 

 process occurring during disintegration. From the theory 

 of the structure of the atom originally put forward by 

 Prof. Sir E. Rutherford*, it is probable that both a and (3 

 rays originate in the central positive nucleus, while 7 rays are 

 a secondary effect due to the arrangement of the electrons. 

 It thus appears probable that the ultimate cause of disinte- 

 gration is connected with the structure of the nucleus rather 

 than that of the atom as a whole, so that a study of radio- 

 active transformation is one possible method of obtaining 

 information on the properties of the nucleus. From the fact 

 that the radiations emitted follow practically the same order 

 in the three radioactive families, it would appear that the 



* Cf. Bohr, Phil. Mag. xxvi. p. 501 (1913). Rutherford & Robinson, 

 Phil. Mag. xxvi. p. 728 (1913). Rutherford, Phil. Mag. xxvii. p. 488 

 (1914). 



