EN MGab tod 
LXIL. Slow Transformation Products of Radium. By B. 
RourHerrorD, F.RS., Macdonald Professor of Physics, 
McGill University, Montreal *. 
T has been previously shown that radium undergoes 
disintegration through a series of well marked stages. 
The radium first of all produces the radium emanation, and 
this in turn is transformed into an active deposit, which 
behaves as a solid, and gives rise to the phenomena of excited 
activity. 1 have recently shown that this active deposit 
undergoes three further rapid transformations t. For con- 
venience, the products in the active deposit will be termed 
Radium A, Radium B, and Radium C respectively §. The 
change from A to B is accompanied by @ rays alone, the 
change B into C is a rayless change, while the change C 
into D gives rise to a, 8, and y rays. The time T for each 
of the products of radium to be half transformed is shown in 
the following table :-— 
li Rays. 
RADIUM, xaieiuieuad Shey Gybiegtieee a Yays. 
XADIUM EMANATION .. 4 days a Tays. 
PADDUM AV i eee ae 3 minutes a Trays. 
Ripru BS actve 21 minutes no rays. 
deposit 
amin  Ookiiab wie ws 28 minutes a, B, y rays. 
The changes in radium are not, however, completed at this 
stage, for it will be shown that there is very strong evidence 
that there are at least two more slow transformations. 
M. and Mme. Curie || observed that a body exposed in the 
presence of radium emanation did not, after removal, com- 
pletely lose all its activity. A residual activity always 
remained, which they state was of the order of 1/20,000 of 
the initial activity. It will be seen later, however, that the 
magnitude of this residual activity depends not only on the 
amount of emanation to which the body has been exposed, 
but also on the time of exposure. For an exposure of several 
* Communicated to the International Electrical Congress, St. Louis, 
Sept. 16, 1904. Communicated by the Author. 
+ Rutherford and Soddy, Phil. Mag. April & May 1908. 
t Bakerian Lecture, Roy. Soc. Lond. 1904. 
§ Note-——The term emanation X, which I previously employed to 
designate the matter Radium A, is not very suitable, and I have discarded 
it in favour of the present nomenclature, which is simple and elastic. 
|| Theses presentées a la Faculté des Sciences, Paris, 1903, p. 116. 
