Energy of Rontgen and Bccquerel Rays, Sfc. 245 



" Energy of Eontgen and Becquerel Kays and the Energy required 

 to produce an Ion in Gases." By E. RUTHERFORD, M.A., B.Sc., 

 Macdonald Professor of Physics, and R K McCLUNG, B.A., 

 Demonstrator in Physics, McGill University, Montreal. 

 Communicated by Professor J. J. THOMSON, E.R.S. Received 

 June 15, Read June 21, 1900. 

 (Abstract.) 



The primary object of the investigations described in the paper was 

 the determination of the energy required to produce a gaseous ion 

 when X rays pass through a gas, and to deduce from the result the 

 amount of energy radiated out into the gas by uranium, thorium, and 

 the other radio-active substances. 



In order to determine this " ionic energy " it has been necessary to 

 accurately measure the heating effect of X rays and the absorption of 

 Rontgen radiation in passing through a gas. 



The coefficient of transformation of a fluorescent screen excited by 

 X rays as a source of light has also been investigated, and a simple 

 practical method of expressing the intensity of Rontgen radiation in 

 absolute measure has been explained. 



The method adopted to determine the ionic energy was briefly as 

 follows : 



The maximum current between two electrodes produced by the 

 ionization of a known volume of the gas by the rays was determined. 



In order to ionize the gas energy has to be absorbed, and the 

 intensity of the radiation falls off more rapidly than the law of inverse 

 squares. Assuming that the energy of the radiation absorbed in the 

 gas is expended in the production of ions, then, knowing the coefficient 

 of absorption of the rays in the gas, the total current produced by the 

 complete absorption of the whole radiation given out by the bulb into 

 the gas can be deduced. 



Let i = maximum current produced by the total ionization of the 



gas by the rays, 

 n = number of ions produced, 

 e = charge on an ion. 

 Then i = ne. 

 Let H = heating effect due to the rays when absorbed in a metal, 



E = total energy of the rays in ergs, 

 Then E = JH, where J = Joule's equivalent. 



If W = average energy required to produce an ion, then 

 nW = E = J.H, 

 w JH JH* 



.'. W = = : 



n i 



