﻿430 Sir E. Rutherford and Dr. J. Chadwick on the 



liberated from the active elements probably existed as 

 satellites circulating in orbits round the main nucleus. In 

 the case of an effective collision of an a particle with such 

 a nucleus, part of the momentum of the a particle is com- 

 municated to the central nucleus, but the satellite is 

 sufficiently distant from the latter to acquire enough 

 momentum and energy to escape from the system. It was 

 shown that such a point of view offers a general explana- 

 tion of the variation of the velocity of the expelled H 

 nuclei with the speed of the a particle and also of the escape 

 of the H nuclei in all directions. The chance of ejecting 

 an H satellite at high speed from a nucleus is much smaller 

 (for nitrogen, for example, about 1/20) than the chance of 

 setting a free H nucleus in correspondingly rapid motion. 

 It appears therefore that the release of the satellite only 

 takes place under certain restricted conditions of the 

 collision of the v particle with the nucleus. If the H 

 satellites were present in lithium and chlorine and were very 

 lightly bound to the nucleus, it is to be anticipated that 

 the number released by the a rays would be of the same 

 order of magnitude as if the H nuclei were free. As this 

 is found not to be the case, we may conclude that neither 

 lithium nor chlorine has any lightly bound satellites in its 

 nuclear structure. The complete absence of long-range 

 particles from these elements shows that the H satellites, if 

 they are present at all, are strongly bound to the main 

 nucleus. If, for example, the satellite revolves very close to 

 the nucleus, the a particle may only be able to give such a 

 small part of its momentum to the satellite that it is unable 

 to release it from the system. It does not, however, seem 

 likely that the forces binding a satellite would vary greatly 

 in passing from phosphorus to chlorine. It seems more 

 probable that the general structure of the chlorine nucleus 

 differs in some marked way from that of the group of active 

 elements. The H nuclei may perhaps be definitely incor- 

 porated into the main nuclear system, so that the a particle 

 has no chance of concentrating its energy upon a single unit 

 of the nuclear structure. In a similar way it seems probable 

 that lithium must differ widely in structure from the suc- 

 ceeding element boron. The facts brought to light in these 

 experiments indicate that the nuclei even of light elements 

 are very complex systems and illustrate how difficult it will 

 be to find any simple and general rule to account for the 

 variation in structure of successive elements. 



It has been pointed out that, with the exception of the first 



