Artificial Disintegration of Light Elements. 813 



Long-range Particles from Nitrogen. 



In these experiments the source of ol rays was always fixed 

 at 3 5 cm. from the zinc-sulphide screen and a continuous 

 stream of dry air was drawn through the apparatus. The 

 number of particles was counted after passing through mica 

 screens of different stopping power. 



Curve A (fig. 2) is a typical absorption curve of the 



Fiff. 2. 



\lkht crts a 



particles from nitrogen using radium as a source of a rays. 

 The ordinates represent the number of scintillations observed 

 per minute per milligram of activity of radium C measured 

 by y rays; the abscissa?, the stopping power of the absorbing 

 screens for a particles expressed in terms of centimetres of 

 air. It is seen that scintillations were observed up to 40 cm. 

 absorption. Curve B is the corresponding absorption curve 

 when the a rays passed through a mixture of hydrogen 

 and carbon dioxide, about 1 volume of II 2 to 1*5 of C0 2 , 

 which gave the same stopping-power as air for a rays. It is 

 seen that no H atoms were observed beyond 29 cm. of 

 absorption, but the number rose very rapidly with diminishing 

 absorption. The actual number of scintillations from nitro- 

 gen for 12 cm. absorption was very much less than the 

 number liberated in the H 2 and C0 2 mixture. Curve C 

 represents the "natural" effect when the nitrogen was 

 replaced by dry oxygen. The scintillations observed in this 

 case are believed to have their origin from a slight hydrogen 

 contamination of the source of a rays. 'Phis natural effect 

 is small compared with that shown by nitrogen. 



Curve I) is an illustration of the effects observed when a 



