586 Collision of a. Particles with Light Atoms. 



Discussion of results. 



From the results so far obtained it is difficult to avoid the 

 conclusion that the long-range atoms arising from collision of 

 a particles with nitrogen are not nitrogen atoms but probably 

 atoms of hydrogen, or atoms of mass 2. If this be the case, 

 we must conclude that the nitrogen atom is disintegrated 

 under the intense forces developed in a close collision with a 

 swift a particle, and that the hydrogen atom which is liberated 

 formed a constituent part of the nitrogen nucleus. We have 

 drawn attention in paper III. to the rather surprising obser- 

 vation that the range of the nitrogen atoms in air is about 

 the same as the oxygen atoms, although we should expect a 

 difference of about 19 per cent. If in collisions which give rise 

 to swift nitrogen atoms, the hydrogen is at the same time 

 disrupted, such a difference might be accounted for, for the 

 energy is then shared between two systems. 



It is of interest to note, that while the majority of the 

 light atoms, as is well known, have atomic weights repre- 

 sented by 4n or 4n-f-3 where n is a whole number, nitrogen 

 is the only atom which is expressed by 4u + 2. We should 

 anticipate from radioactive data that the nitrogen nucleus 

 consists of three helium nuclei each of atomic mass 4 and 

 either two hydrogen nuclei or one of mass 2. If the H nuclei 

 were outriders of the main system of mass 12, the number of 

 close collisions with the bound H nuclei would be less than if 

 the latter were free, for the a particle in a collision comes 

 under the combined field of the H nucleus and of the central 

 mass. Under such conditions, it is to be expected that the 

 « particle would only occasionally approach close enough to 

 the H nucleus to give it the maximum velocity, although in 

 many cases it may give it sufficient energy to break its bond 

 with the central mass. Such a point of view would explain 

 why the number of swift H atoms from nitrogen is less than 

 the corresponding number in free hydrogen and less also than 

 the number of swift nitrogen atoms. The general results 

 indicate that the H nuclei, which are released, are distant 

 about twice the diameter of the electron (7 x 10~ 13 cm.) from 

 the centre of the main atom. Without a knowledge of the 

 laws of force at such small distances, it is difficult to estimate 

 the energy required to free the H nucleus or to calculate the 

 maximum velocity that can be given to the escaping H atom. 

 It is not to be expected, a priori, that the velocity or range 

 of the H atom released from the nitrogen atom should be 

 identical with that due to a collision in free hydrogen. 



Taking into account the great energy of motion of the 

 a particle expelled from radium C, the close collision of such 



