Hydrogen Nuclei from Swift- a. Particles. 897 



4. Quantities derived from the Absorption Curves giving 

 information as to the nature of the collision. 



If it be assumed that all the energy of a hydrogen 

 nucleus thrown forward by collision with an a particle 

 is dissipated in producing* ions (an assumption that is 

 almost certainly approximately true), the actual number of: 

 recoil atoms thrown within various angles o£ the incident 

 a. ray can be calculated from curves such as Gr and H. 

 From these numbers, information may be obtained relative 

 to the nature of the collision and the size of the a particle. 

 This question will be considered further in section 6. The 

 steps in the calculation by which the numbers are derived 

 from the absorption curves are outlined in the next section. 



The quantities in Table I. are as follows : — The first 

 column gives the number of recoil atoms whose path after 

 collision makes an angle less than cf> with the incident a. ray. 

 These numbers refer to one a particle passing through 1 cm. 

 of hydrogen gas at N.T.P. The second column gives </>. 

 The third gives the highest potential that the recoiling 

 nucleus reaches in the field (assumed purely electrostatic) of 

 the a particle. y\°\ 3." 



N 



N, the number of recoil atoms thrown within <p of the 

 direction of motion of the a particle, is shown plotted 

 against <j> in fig. 3. 



