442 Mr Whiddington, Note on the Velocity of X-ray Electrons 



Note on the Velocity of X-ray Electrons. By E. Whiddington, M.A. 

 [Received 5 August 1921.] 



It has been known for many years that X-rays have the power 

 of ejecting high speed electrons from the surface of materials on 

 which they are incident. 



The earhest attempts to determine the velocities of these electrons 

 were made by Dorn in 1900 and Innes in 1907. Their general 

 results being that the velocity, as measured by photographic records 

 of the curvature in a known magnetic field, lay between 6 and 

 8 X 109 cm./sec. and was independent of the intensity of the exciting 

 radiation. 



In 1912 the problem was attacked from a different angle, by 

 interpreting the absorption experiments of Beatty . It had previously 

 been shown that a fourth power law of velocity absorption was 

 quite fairly accurately true for fast moving electrons such as those 

 ejected by X-rays*. 



Beatty having measured, in essence, the range in air of the 

 electrons ejected by various quahties of X-ray it was therefore 

 possible to deduce their velocity*. 



In the paper cited it was shown that the velocity of t\ie fastest 

 electrons ejected by X-rays was very nearly equal to 10^ x A, 

 where A is the atomic weight of the radiator supplying the X-rays! 

 It was further predicted that future work should show the existence 

 of two sets of electrons of definite speeds. 



In the early months of this year de Broghef pubHshed a short 

 account of some highly important results in which by using a 

 Coohdge X-ray tube he was able to take magnetic photographs of 

 X-ray electrons with only an hour's exposure. 



The present experiments were then in progress and it seems 

 worth while now to pubhsh a prehminary account of the apparatus 

 finally adopted and initial results obtained. 



The problem resolves itself into obtaining as strong a source 

 of X-rays as possible, causing them to pass through a thin sheet 

 of sohd matter and observing the magnetic spectrum on the 

 emergent side. De Broghe used a Coohdge tube to provide a 

 powerful source of X-rays, a method which commends itself on 

 the grounds of simpHcity and ease of working. 



The first attempts I made were with an apparatus consisting 

 of a fine sht covered with thin metal foil on which Cathode-rays 

 were focussed, the electrons ejected from the emergent side being 

 subject to magnetic deviation on a photographic film. Photographs 



* Whiddington, Proc. Boy. Soc. 1912. 

 t Be Broglie, Comptes Eendus, 1921. 



