XX. Proceedings. [May i^t/i, 19 19. 



General calculation shovv^s that the range of the lighter 

 atoms set in swift motion by close collisions with a 

 particles should be less than that of the a particle if the 

 recoiling atom carries two charges, but should exceed the 

 range of the a particle if the atom carries unit charge. A 

 number of bright scintillations were observed in air and 

 oxygen and carbon dioxide beyond the range of the a 

 particles. The equivalent range of these recoil atoms was 

 found to be about the same in air and oxygen and about 

 1-3 times that of the incident particle. The same general 

 effects were observed in these gases as in hydrogen. The 

 recoil atoms appear to be projected mainly in the direc- 

 tion of the a particles and are more numerous than is to 

 be expected from the simple theory of point charges. The 

 nuclei of the atoms of oxygen and nitrogen appear to 

 have a radius almost twice the diameter of the electron. 



An interesting effect was observed in passing a particles 

 through dry air but not in dry oxygen or carbon dioxide. Not 

 only were bright scintillations observed in air due to singly 

 charged atoms of nitrogen and oxygen of range 1-3 times 

 that of the a particle, but a number of fainter scintillations 

 appeared whose range was about four Limes that of the a 

 particle. These long range scintillations were of about 

 the same brightness as H atoms produced under corres- 

 ponding conditions and were observed for about the same 

 distance. The number of these scintillations in dry air 

 was about the same as the number of H scintillations 

 observed when 6 cms. pressure of hydrogen is added to 

 oxygen. 



As a result of a series of experiments it was found 

 that these long range atoms in air arise from the impact of 

 a particles with nitrogen atoms and presumably are either 

 atoms of hydrogen or atoms of mass 2 disrupted from the 

 nitrogen nucleus. From general radioactive data, it appears 

 probable that the nitrogen nucleus of mass 14 consists of 

 three helium nuclei of mass 4 plus two hydrogen nuclei 

 or one of mass 2. The general results derived receive an 

 explanation if it l)e supposed that the H nuclei are 

 satellites of the main nucleus of mass 12 extending to a 

 distance about twice the diameter of the electron from the 

 centre. It is hoped later to determine the mass and 

 velocity of the large range atoms in nitrogen, but the ex- 

 periments are difficult unless Very intense sources of radia- 

 tion are used. Taking into account the great energ)^ of 

 motion of the a particle, it is to be anticipated that under 

 the intense forces brought into play in such close collisions 

 the nuclei should be much deformed and under favourable 

 conditions disrupted into two or more constituents. 



