Artificial Disintegration of Light Elements. 819 



with the number in a forward direction. For an absorption 

 of 18 cm., the number was certainly less than 1/50 of the 

 corresponding number in the forward direction. 



We have not so far been able to make similar experi- 

 ments with the particles from boron, fluorine, sodium, or 

 phosphorus. 



Discussion of Results. 



Experimental evidence shows that the long-range particles 

 expelled from nitrogen are swift H atoms earring a unit 

 positive charge. While we bave not yet been able to test 

 the nature of these long-range particles liberated from other 

 elements, it seems very probable that tbe particles are in all 

 cases H atoms, which are released at different maximum 

 speeds depending on the nature of the element and on the 

 velocity of the incident a particle. Under the conditions of 

 the experiments, such H atoms can only arise from a disin- 

 tegration of the nucleus brought about by a close collision 

 with an a particle. 



It is of interest to note that of the elements so far examined 

 only those whose atomic mass is given by 4n + 2 or 4?i + 3, 

 where n is a whole number, give rise to H atoms. Elements 

 of mass 4>i like carbon, oxygen, sulphur, show no effect. 

 This result is clearly seen from the following table of ele- 

 ments which give H atoms: — 



Element. Mass. A.n-\-a. 



Boron 11 2x4 + 3 



Nitrogen 14 3x4 + 2 



Fluorine 19 4x4+3 



Sodium 23 5x4 + 3 



Aluminium 27 6x4 + 3 



Phosphorus 31 7x4+3 



This result receives a simple explanation on the assumption 

 that the nuclei of these elements are built up of helium 

 nuclei of mass 4 and of hydrogen nuclei. The importance 

 of: the helium nucleus as a unit of atomic structure in heavy 

 elements is clearly brought out by the study of the radio- 

 active transformations. 



In order to account for the liberation of an 11 atom at 

 high speed, it is natural to suppose that the H nuclei arc 

 satellites of the main nucleus. In a close collision, the 

 ol particle is able to give sufficient energy to the satellite to 

 cause its escape at high speed from the central nucleus. 



