THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OK SCIENCE. 



[SIXTH SERIES.] 



JUNE 1919. 



LI. Collision of a Particles with Light Atoms. I. Hydrogen. 

 By Professor Sir E. Rutherford, F.R.S* 



§ 1. i^VN the nucleus theory of atomic structure, it is to be 

 \_s anticipated that the nuclei of light atoms should 

 be set in swift motion by intimate collisions with a. particles. 

 From consideration of impact, it can be simply shown that as 

 a result of a head-on collision, an atom of hydrogen should 

 acquire a velocity 1*6 times that of the a particle before 

 impact, and should possess *64 of the energy of the incident 

 a particle. Such high speed "H ; ' atoms should be readily 

 detected by the scintillation method This was shown to 

 be the case by Marsden f, who found that the passage of 

 a particles through hydrogen gave rise to numerous faint 

 scintillations on a zinc sulphide screen placed far beyond 

 the range of tbe a. particles. The maximum range of the 

 H particles, set in motion by the a. particles from radium C, 

 was over 100 cm. in hydrogen or about four times the range 

 of the colliding a particles in that gas. This range agreed 

 well with the value calculated by Darwin t from Bohr's § 

 theory of the absorption of a particles by matter. 



In most of the experiments of Marsden, a thin glass a-ray 

 tube, containing purified radium emanation, was used as an 

 intense source of rays. This was placed in a closed vessel at 

 a suitable distance from a zinc sulphide s Teen, and the space 



* Communicated by the Author. 

 t Marsden, Phil. Mag. xxvii. p. 824 (1914). 

 X Darwin, Phil. Mag-, xxvii. p. 499 (1914). 

 § Bohr, Phil. Mag. xxv. p. 10 (1913). 



Phil. Mag. S. 6. Vol. 37. No. 222. June 1919, 2 P 



