Artificial Disintegration of Light Elements. 821 



that the presence of the central nucleus greatly diminishes 

 the chance of such a direct collision with the H satellite as 

 will give it sufficient velocity to escape from the system. It 

 may be that it is only within certain prescribed limits of velo- 

 city of the satellite and position with regard to the central 

 nucleus that a liberation of the satellite at a high speed by 

 an ol particle is possible. 



In discussing the possible mechanism of release of an 

 H atom from a nucleus by the close collision with an 

 a particle, two important experimental facts should be borne 

 in mind — viz. (1) the maximum velocity of escape of an 

 H atom for a given element is, at any rate to a first approxi- 

 mation, proportional to the velocity of the colliding a particle ; 

 (2) in the case of aluminium and possibly of the other elements, 

 the H atoms escape in all directions, but the velocity is less 

 in the backward than in the forward direction. The data in 

 the case of aluminium and nitrogen are collected in the 

 following table. Since the velocities of the H atoms are 

 nearly proportional to the velocity V of the .colliding 

 a particle, the velocity, momentum, and energy of the 

 H atom are expressed in terms of the incident a particle. 





Velocity. 



Momentum. 



Kinetic energy 



Incident ct particle 



V 



4V 



2 V 2 



H atoms from aluminium : 









(1) in forward direction 



.. 2-37 V 



2-37V 



2-8 IV 2 



(2) in backward direction . 



.. 2-13V 



- 213V 



2-27V 2 



H atoms from nitrogen : 









(1) in forward direction .... 



.. 1-80V 



1-80V 



T62V 2 



The velocities are calculated on the assumption that the 

 maximum velocity of a free H atom is 1*6 V and that the 

 corresponding range is 28 cm. of air for an a particle of 7 cm. 

 range. It is assumed from analogy with a particles that the 

 velocity of an H atom is proportional to the cube root of its 

 range. The general evidence indicates that this relation 

 holds, at any rate, approximately. It is seen that the energv 

 of the H atom escaping from aluminium is 1*40 times the 

 energy of the incident a particle, and even in the backward 

 direction the energy is 13 per cent, greater. This additional 

 energy must come from the atom in consequence of its 

 disintegration. 



Mechanism of Disintegration. 



It is of interest. to consider whether any further infor- 

 mation can be obtained which will throw lighi on the 



