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BELL SYSTEM TECHNICAL JOURNAL 



In giving the data for Fig. 2, as my words have implied, only a 

 single fragment from each fission escaped into the gas of the ionization- 

 chamber; this was arranged by laying down a very thin film of uranium 

 upon a thick sheet of another metal. Figure 3 was obtained by laying 

 down the uranium film upon a foil so very thin, that from most of the 

 fissions both of the fragments entered into the gas. The great peak of 

 Fig. 3 therefore indicates the sum of the energies of the fission-frag- 

 ments, the peaks of Fig. 2 the components of that sum. Making al- 



Fig. 3 — Distribution-In-energy of pairs of fission-fragments from uranium. 

 (Kanner and Barschall) 



lowance for the average energy-loss suffered by the fragments in 

 passing through solid matter before they escape to the gas, Kanner and 

 Barschall decide on 159 Mev. for the sum, 98 and 65 Mev. for the 

 components: the discrepancy between 159 and (98 -f 65) lies within 

 the uncertainty of experiment. By the law of conservation of momen- 

 tum, the ratio of the component energies is the ratio of the fragment- 

 masses; if one of these is about 100, the other is therefore about 150 — 

 and the uncertainty implied by "about" is broad enough to permit 

 the hypotheses which we have made and are to make about the nature 



