a Particles with Light Atoms. 573 



example, in a collision of an a particle with the helium 

 nucleus of equal mass, the range of the helium atom should 

 be the same as the a particle before the collision if it carries 

 two charges, but four times this range if it carries one 

 charge. 



We have collected in the following table data connected 

 with the collision of a. particles with the lighter atoms of 

 matter. The maximum velocity, momentum, and energy 

 of the atom after collision are given as fractions of that of 

 the incident a particle. The range is calculated on the 

 assumption that it is proportional to the power 2*9 of the 

 velocity and that the atom carries unit charge. 



For convenience, the data for hypothetical atoms of mass 

 2 and 3 times that of hydrogen are included. 



Table I. 



Element. 



Hydrogen .. 



? 



Helium 



Lithium 



Beryllium .. 



Boron 



Carbon 



Nitrogen . . 



Oxygen 



Fluorine 



Neon 



Sodium 



Magnesium 

 Aluminium 



Iron 



Silver 



Gold 





Ratio of 



Ratio of 



Ratio of 



Ratio of 



Atomic 

 weight. 



1 



velocity 

 to that of 

 a particle. 



momentum 

 to that of 

 a particle. 



energy 

 to that of 

 a particle. 



to that of 



incident 



a particle. 



16 



•4 



•64 



3-91 



2 



1-33 



•66 



•89 



4-6 



3 



1-14 



•85- 



•98 • 



5-05 



4 



100 



100 



1-00 



4-00 



7 



•727 



1-27 



•925 



2-78 



9 



•615 



1-38 



•85 



2-20 



11 



•533 



1-46 



•78 



1-77 



12 



•500 



1-50 



•75 



1-61 



14 



•444 



1-55 



•69 



1-33 



16 



•400 



1-60 



•64 



112 



19 



•348 



1-65 



•575 



•89 



20 



•333 



1-67 



•55 



•82 



23 



•296 



1-70 



•50 



•67 



24 



•286 



1-71 



•49 



•64 



27 



' -258 



1-74 



•45 



•53 



56 



•133 



1-86 



•25 



•19 



108 



071 



1-92 



•136 



•05 



197 



•040 



1-92 



•079 



•017 



It is seen that, on the assumption of unit charge, all the 

 atoms of atomic weight up to oxygen should be detected 

 beyond the range of the a particle. Supposing that 

 a. particles of range 7 cm. are used, the maximum range 

 to be expected for unit charge are for He 28*0, Li 19'6, 

 Be 15 4, Bo 124, C 11% N 9 3, O 7"8 cm. 



Some preliminary experiments have been made with 

 helium, using the apparatus similar to that employed for 



hydro 



gen and 



described in paper I. but on a smaller scale. 



