Transformations in the Active Deposit of Actinium. 701 



nuclei of corresponding products must have some fundamental 

 characteristic in common. 



In the following table the disintegration constants and 

 properties of the products following the emanations are 

 given, the numbers in the same row belonging to the family 

 given in the first column. The a rays are characterized by 

 their ranges in air at 15° C. and 76 cm. Hg, and the j3 and 

 7 rays by their respective absorption coefficients in alu- 

 minium, the numbers for y rays being taken from the tables 

 of Rutherford and Richardson*. For theoretical purposes 

 and for the establishment of empirical formulae it would, 

 no doubt, be better to give the velocities of the a and j3 par- 

 ticles and the actual wave-lengths of the various y rays, but 

 such data are not yet complete and the numbers given are 

 sufficient for qualitative comparisons. In the columns for 

 C« and C^are given the data for those atoms of the 

 products which emit a and /3 rays respectively, and the 

 chances of disintegration in any second in these two directions 

 are denoted by A a and A^t, where \ a + \p = \ n (X c = the 

 ordinary disintegration constant of C) and \ a /\p is the ratio 

 of the numbers of atoms which are transformed in the two 

 ways. It is obvious that the D products of actinium and 

 thorium correspond to radium C 2 , and the data for these 

 products has therefore been placed in the same column, and 

 similarly for the other corresponding products. When the 

 schemes of transformation are fully investigated, a change ot 

 nomenclature will be advisable. 



It will be noticed that in almost every column the thorium 

 product lies intermediate in its characteristics between the 

 corresponding products of radium and actinium. No direct 

 information is at present available as to whether this is also 

 the order of the atomic weights *. An exception occurs 

 in the B products, the transformation constants and the 

 absorption coefficients of the hardest y rays both following 

 the order Ra >- Act > Th. On the supposition mentioned 

 above, this would apparently show that whatever irregularity 

 there is in the nucleus of one of the products, it must also 

 extend to one of the innermost rings of electrons. This 

 question cannot be settled definitely, however, until the 

 wave-lengths of the y rays are known. Another exception 

 is that the ranges of the particles of the C 2 products, ( = RaC v ) 

 follow the order Th > Ra > Act. In fact Swinne§, using 



* Rutherford & Eichardson, Phil. Mag. xxvi. p. 938 (1913). 



t Marsden & Darwin loc. cit. 



% Of. Fajans, Phys. Zeit. xiv. p. 5 (1913). 



§ Swinne, Phys. Zeit xiv. p. 142 (1913). 



PHI. Mag. S. 6. Vol. 27. No. KG. Jj til 1914. 3 A 



