SECTIONAL TRANSACTIONS. 



SECTION A. 

 MATHEMATICAL AND PHYSICAL SCIENCES. 



Thursday, August 18. 



Symposium on Nuclear physics (lo.o). 



Prof. N. Bohr. — Introduction. 



Due to the extreme facility of energy exchange between the closely 

 packed particles in atomic nuclei, nuclear reactions show certain typical 

 features which differ strikingly from those of ordinary atomic reactions. 

 In particular nuclear transmutations initiated by collisions with heavy 

 particles take place in two well-separated stages of which the first consists 

 in the formation of a semi-stable compound nucleus, where the excitation 

 energy is distributed among the nuclear particles in a similar way to that 

 in a heated body, and the second in the subsequent disintegration of this 

 system or its de-activation by emission of radiation, exhibiting instructive 

 analogies to evaporation or thermal radiation respectively. Similarly the 

 excitation of nuclei by radiation, resulting in the release of heavy particles, 

 suggests a comparison with the well-known phenomena of selective ab- 

 sorption of infra-red radiation by solid or liquid substances. It is shown how 

 these views combined with simple arguments of quantum theory account 

 in a comprehensive way for the experimental evidence regarding such 

 nuclear phenomena. 



Prof. W. BoTHE. — Some results concerning nuclear levels (10.45). 



The general outlines of the spectroscopic investigation of atomic nuclei 

 are briefly given. Some new results are communicated and the following 

 cases of special interest are dealt with in detail : 



(i) Resonance levels occurring with (n, a)-reactions. 



(2) Connection between the resonance levels in a case of branched 

 reaction. 



(3) The nuclear photoelectric effect. 



(4) Nuclear levels occurring with the (3-decay. 



Dr. J. D. CocKCROFT, F.R.S. — The High-Voltage Laboratory and 

 Cyclotron of the Cavendish Laboratory and their application to 

 nuclear research (11.30). 



The Cavendish Laboratory has recently extended its equipment for 

 nuclear research by the building of a High Voltage Laboratory and a 

 Cyclotron. The High Voltage Laboratory houses a i-2 million volt D.C.. 



