SECTIONAL TRANSACTIONS.— A. 307 



of the dimensions of the nucleus. It is not possible to define in any exact 

 way the energy of an electron which is in some way confined to such a small 

 structure — that is to say, to a region of space whose dimensions are smaller 

 than the wave-length of the de Broglie wave of the electron. As the energy 

 of the electron when in or attached to the nucleus is incapable of specifica- 

 tion, it is not surprising that the energies of the emitted electrons should be 

 represented by a curve representing a probability distribution rather than 

 by definite discrete values. This is not, of course, an explanation of the 

 detailed structure of such distribution curves, but I believe that this struc- 

 ture will be found to depend fundamentally, and in some such way as I have 

 indicated, on the smallness of the linear dimensions of the nucleus. 



Discussion on The neutron (Dr. J. Chadwick, F.R.S. ; M. le Due 

 DE Broglie ; Prof. O. W. Richardson, F.R.S. ; Dr. N. Feather ; 

 Mr. P. I.Dee):— 



Dr. J. Chadwick, F.R.S, 



An account was given of the evidence which led to the discovery that in 

 some cases of artificial transmutation by a-particles, notably those of beryl- 

 lium and boron, neutral particles are emitted. The mass of these neutrons 

 can be deduced from experiment ; it is probably between i -005 and i -008. 

 This suggests very strongly that the neutron is not an elementary particle 

 but is formed by the close alliance of a proton and an electron. Such a 

 particle will have a very small electric field except at very close distances, 

 and will therefore only rarely be deflected by atomic nuclei in its passage 

 through matter. It should be able to enter easily an atomic nucleus and 

 occasionally cause a disintegration . Some cases of disintegration by neutrons 

 have already been observed by Feather. 



M. LE Due DE Broglie. 



Experiments on the absorption and scattering of neutrons in their passage 

 through matter were described. The relative scattering of different atomic 

 nuclei seems to depend markedly on the velocity of the neutron, and he 

 suggested that this anomalous behaviour may be analogous to the Ramsauer 

 effect. 



Prof. O. W. Richardson, F.R.S. 



These investigations are going to lead to many important developments. 

 As an illustration I will mention some interesting possibilities in connection 

 with the building-up of nuclei out of neutrons and protons. These have 

 been put forward by J. H. Bartlett, but they may be unfamiliar to some of 

 you. Starting with the proton H\ we add a neutron and get the hydrogen 

 isotope H^. If we add first a proton and then a neutron, we should get in 

 succession He^ and He*. We can regard this as a building-up process 

 analogous to the completion of the K shell in extranuclear atomic structure. 

 After this we reverse the order of alternate addition, and so proceed up to 

 O". We may regard this stage as the nuclear analogue of the completion 

 of the L shell. At this stage we change the addition process again, adding 

 successively two neutrons, then two protons, and then repeating. We carry 

 this on until we reach A^*, which we may regard as the nuclear analogue 



